HomeMy WebLinkAboutMS 2021-0001; GARFIELD HOMES; REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION; 2020-12-09
REPORT OF PRELIMINARY GEOTECHNICAL
INVESTIGATION
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
JOB NO. 20-12942
09 December 2020
Prepared for:
Rincon Homes
09 December 2020
Rincon Homes Job No. 20-12942
5315 Avenida Encinitas, Suite 200
Carlsbad, CA 92008
Attn: Mr. Thomas St. Clair
Subject: Report of Preliminary Geotechnical Investigation
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
Dear Mr. St. Clair:
In accordance with your request, and our work agreement of September 28, 2020,
Geotechnical Exploration, Inc. has performed a preliminary geotechnical
investigation for the subject project in Carlsbad, California. The field work was
performed on October 26, 2020.
If the conclusions and recommendations presented in this report are incorporated
into the design and construction of the proposed four two-story, single family
residences with attached garages, detached accessory dwelling units, and associated
improvements, it is our opinion that the site is suitable for the proposed project.
This opportunity to be of service is sincerely appreciated. Should you have any
questions concerning the following report, please do not hesitate to contact us.
Reference to our Job No. 20-12942 will expedite a response to your inquiries.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________ ______________________________
Jaime A. Cerros, P.E. Hector G. Estrella, C.E.G.
Senior Geotechnical Engineer Engineering Geologist
R.C.E. 34422/G.E. 2007 P.G. 9019/C.E.G. 2656 (Exp 5/31/22)
TABLE OF CONTENTS
I. PROJECT SUMMARY ............................................................................ 1
II. SCOPE OF WORK ................................................................................ 2
III. SITE DESCRIPTION ............................................................................. 2
IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING .............................. 3
V. LABORATORY TESTING & SOIL INFORMATION ........................................ 4
VI. REGIONAL GEOLOGIC DESCRIPTION ..................................................... 8
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION ................................... 13
VIII. GEOLOGIC HAZARDS ........................................................................ 14
A. Local and Regional Faults ........................................................... 15
B. Other Geologic Hazards ............................................................. 21
IX. GROUNDWATER ............................................................................... 24
X. CONCLUSIONS & RECOMMENDATIONS ................................................ 26
A. Preparation of Soils for Site Development ..................................... 28
B. Seismic Design Criteria .............................................................. 37
C. Foundation Recommendations .................................................... 38
D. Concrete Slab On-Grade Criteria ................................................. 41
E. Retaining Wall Design Criteria ..................................................... 45
F. Slopes .................................................................................... 47
G. Pavements .............................................................................. 49
H. Site Drainage Considerations ...................................................... 50
I. General Recommendations ......................................................... 51
XI. GRADING NOTES .............................................................................. 53
XII. LIMITATIONS ................................................................................... 53
REFERENCES
FIGURES
I. Vicinity Map
IIa-b. Plot Plan and Site Specific Geologic Map
IIIa-e. Exploratory Boring Logs and Laboratory Results
IVa-c. Laboratory Test Results
V. Geologic Map Excerpt and Legend
VI. Schematic Retaining Wall Subdrain Recommendations
APPENDICES
A. Unified Soil Classification System
B. ASCE Seismic Summary Report
REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
JOB NO. 20-12942
The following report presents the findings and recommendations of Geotechnical
Exploration, Inc. for the subject project.
I. PROJECT SUMMARY
It is our understanding, based on our review of the available plans prepared by Kirk
Moeller Architects, Inc., and Pasco Laret Suiter and Associates (references), that the
existing two-story, split-level single-family residential structure and the existing one-
story building located to the northeastern portion of the property and associated
improvements are to be entirely demolished and replaced with three (3), three-story,
multi-family condominium structures with attached garages, 4- to 6-foot-high
retaining walls, and associated improvements. The new structures are to be
constructed of standard-type building materials utilizing conventional foundations
with concrete slab on-grade. Foundation loads are expected to be typical for this
type of relatively light construction. A preliminary site plan by Kirk Moeller Architects,
Inc., dated August 17, 2020, has been reviewed by us and used to understand the
scope of the project. When final plans are completed, they should be made available
for our review. Additional or modified recommendations will be provided at that time
if warranted.
Based on the available information at this stage, it is our opinion that the proposed
site development would not destabilize neighboring properties or induce the
settlement of adjacent structures or improvements if designed and constructed in
accordance with our recommendations.
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Carlsbad, California Page 2
II. SCOPE OF WORK
The scope of work performed for this investigation included a site reconnaissance and
subsurface exploration program under the direction of our geologist with placement,
logging and sampling of five exploratory trenches, review of available published
information pertaining to the site geology, laboratory testing, geotechnical
engineering analysis of the field and laboratory data, and the preparation of this
report. The data obtained and the analyses performed were for the purpose of
providing design and construction criteria for the project earthwork, building
foundations, retaining walls, slab on-grade floors and associated improvements.
III. SITE DESCRIPTION
The lot is known as Assessor’s Parcel No. 206-080-01-00, with a current address of
4008 Garfield Street in the City of Carlsbad, County of San Diego, State of California.
Refer to Figure No. I, Vicinity Map, for the site location.
The rectangular shaped lot square footage is reported in the referenced plans as
6,001 square feet/0.14 AC. The property is bordered on the north by Chinquapin
Avenue, to the west by Garfield Street; and on the east and south by two single-
family residential structures. Refer to Figure Nos. IIa-b, Plot Plan.
The existing property is currently developed with a two-story, split-level, single-
family residential structure and an existing one-story building located to the
northeastern portion of the property, landscape areas and associated improvements.
Vegetation on the site primarily consists of an ornamental garden, shrubbery, weeds,
grasses and mature trees.
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The property slopes down from the western property line to the eastern property line.
Approximate elevations across the property range from approximately +59 feet
above Mean Sea Level (MSL) along the eastern side of the site to approximately +67
feet above MSL at the western portion of the property. Survey information
concerning elevations across the site was obtained from the topographic survey
template of the preliminary site plan by Pasco Laret Suiter, dated August 03, 2020.
IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING
The field investigation was conducted on October 26, 2020, and consisted of surface
reconnaissance and a subsurface exploration program utilizing hand-excavated
exploratory test trenches to investigate and sample the subsurface soils. Five (5)
exploratory trenches (HP-1 to HP-5) were excavated to a maximum depth of 5 feet
in the areas of the proposed development and associated improvements. The
excavations revealed that the building site is underlain by approximately 0.5 feet of
loose to medium dense, silty sand fill soil over medium dense, silty sand natural
residual soil, mantling medium dense to dense formational materials. The soils
encountered in the exploratory trenches are considered to have a low expansion
potential with an Expansion Index of less than 50. The exploratory excavations were
continuously logged in the field by our geologist and described in accordance with
the Unified Soil Classification System (refer to Appendix A). The approximate
locations of the exploratory trenches are shown on Figure Nos. IIa-b, the Plot Plan.
Representative samples were obtained from the exploratory trenches at selected
depths appropriate to the investigation. Relatively undisturbed chunk and drive
samples and disturbed bulk samples were collected from the exploratory trenches to
aid in classification and for appropriate laboratory testing. The samples were
returned to our laboratory for evaluation and testing. Exploratory trench logs have
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1. Moisture Content (ASTM D2216-19)
2. Density Measurements (ASTM D2937-17e2)
3. Standard Test Method for Bulk Specific Gravity and Density of
Compacted Bituminous Mixtures using Coated Samples (ASTM
D1188-07)
4. Laboratory Compaction Characteristics (ASTM D1557-12e1)
5. Determination of Percentage of Particles Smaller than #200
Sieve (ASTM D1140-17)
6. Resistivity and pH Analysis (Department of Transportation
California Test 643)
7. Water Soluble Sulfate (Department of Transportation
California Test 417)
8. Water Soluble Chloride (Department of Transportation
California Test 422)
Moisture content and density measurements were performed by ASTM methods
D2216-19 and D2937-17e2 respectively, in conjunction with D1188-07 to establish
the in-situ moisture and density of samples retrieved from the exploratory trenches.
V. LABORATORY TESTING & SOIL INFORMATION
Laboratory tests were performed on retrieved soil samples in order to evaluate their
physical and mechanical properties. The test results are presented on Figure Nos.
IIIa-e and IVa-c. The following tests were conducted on representative soil samples:
been prepared on the basis of our observations and laboratory test results, and are
attached as Figure Nos. IIIa-e.
The exploratory trench logs and related information depict subsurface conditions only
at the specific locations shown on the plot plan and on the particular date designated
on the logs. Subsurface conditions at other locations may differ from conditions
occurring at the locations. Also, the passage of time may result in changes in
subsurface conditions due to environmental changes.
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Measurements were also performed by ASTM method D1188-07, the bulk specific
gravity utilizing paraffin-coated specimens. This method helps to establish the in-
situ density of chunk samples retrieved from formational exposures/outcrops. The
test results are presented on the trench logs at the appropriate sample depths and
laboratory test results.
Laboratory compaction values (ASTM D1557-12e1) establish the optimum moisture
content and the laboratory maximum dry density of the tested soils. The relationship
between the moisture and density of remolded soil samples helps to establish the
relative compaction of the existing fill soils and soil compaction conditions to be
anticipated during any future grading operation. The test results are presented on
the trench logs at the appropriate sample depths and laboratory test results.
The particle size smaller than a No. 200 sieve analysis (ASTM D1140-17) aids in
classifying the tested soils in accordance with the Unified Soil Classification System
and provides qualitative information related to engineering characteristics such as
expansion potential, permeability, and shear strength. Our laboratory testing
indicated 16 percent of the sample passing the No. 200 sieve. The test results are
presented on the trench logs at the appropriate sample depths and laboratory test
results.
The expansion potential of soils is determined, when necessary, utilizing the Standard
Test Method for Expansion Index of Soils (ASTM D4829-19). In accordance with the
Standard (Table 5.3), potentially expansive soils are classified as follows:
EXPANSION INDEX POTENTIAL EXPANSION
0 to 20 Very low
21 to 50 Low
51 to 90 Medium
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91 to 130 High
Above 130 Very high
Based on our visual classification, our laboratory sieve analysis of representative
samples and our past experience with similar soils, it is our opinion that the existing
fill and formational materials of the Old Paralic Deposits, Units 6-7, encountered in
the trenches possess a very low to low potential for expansion. Therefore, we have
assigned a maximum expansion index of less than 50 to these soils.
To assess soil corrosivity of the on-site soils, resistivity, pH, chloride and soluble
sulfate tests were performed by an outside consultant (Clarkson Laboratory and
Supply Inc.), on samples of the near surface soils most likely to be in contact with
concrete and ferrous metals. The most common factor in determining soils corrosivity
to ferrous metals is electrical resistivity. As soil’s resistivity decreases, its corrosivity
to ferrous metals increases. The tested soils yielded low resistivities of 8,800 and
5,800 Ohm-cm indicating that the soils are mildly corrosive to ferrous metals.
Soils and fluids are considered neutral when pH is measured at 7, acidic when pH is
measured at <7 and alkaline when measured at >7. Soils are considered corrosive
when the pH gets down to around 5.5 or less. Results of the laboratory testing yielded
pH values of 7.2 and 6.9, indicating that the tested soils range from slightly acid to
slightly alkaline, indicating that pH is not a significant factor in soil corrosivity to
metals.
Large concentrations of chlorides will adversely affect any ferrous metals such as iron
and steel. Soil with a chloride concentration greater than or equal to 500 ppm (0.05
percent) or more is considered corrosive to ferrous metals. The chloride content of the
tested soils measured at approximately 30 and 10 ppm or 0.003 and 0.0010 percent
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respectively, indicating that chloride is not a major factor in corrosion to ferrous
metals.
The primary cause of deterioration of concrete in foundations and other below ground
structures is the corrosive attack by soluble sulfates present in the soil and
groundwater. The results of water-soluble sulfate testing performed on a
representative sample of the near surface soils in the general area of the proposed
structures, yielded soluble sulfate contents of less than 30 ppm or 0.003 percent,
indicating that the proposed cement-concrete structures that are in contact with the
underlying soils are anticipated to be affected with a negligible sulfate exposure. As
such, there is no restriction on selection of cement type.
The table below summarizes the laboratory results for chemical testing of the
sampled soils:
Sample Location/
Depth, (ft) pH Soluble Sulfate
(PPM)
Soluble Chloride
(PPM)
Soil Resistivity
(Ohm-cm)
HP-2 / 2.0-4.0 7.2 <30 30 5,800
HP-4 / 3.0-5.0 6.9 <30 10 8,800
The laboratory testing results are presented in figures IVa-c
It should be noted that Geotechnical Exploration Inc., does not practice corrosion
engineering and our assessment here should be construed as an aid to the owner or
owner’s representative. A corrosion specialist should be consulted for any specific
design requirement.
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Based on the field and laboratory test data, our observations of the primary soil types,
and our previous experience with laboratory testing of similar soils, our Geotechnical
Engineer has assigned values for friction angle, coefficient of friction, and cohesion
for those soils that will have significant lateral support or load bearing functions on
the project. The assumed soil strength values have been utilized in determining the
recommended bearing value as well as active and passive earth pressure design
criteria for foundations and retaining walls. The assumed strength values for properly
compacted fill and for dense formational soils are 33 degrees and cohesion equal to
50 psf, as well as total unit weight of 120 pcf are based on the visual inspection of
the soils and our experience. With these values we calculated the ultimate bearing
capacity of the soil to be 9,285 psf by Terzaghi’s equation. This value was reduced
with a factor of safety of 3 to calculate the allowable bearing capacity of 3,095 psf,
which has been reduced to the nominal recommended value of 2,500 psf. The active
and passive pressure of the soils were calculated with Terzaghi’s equations for those
pressures and neglecting the cohesion contribution to values of 35.4 pcf and 407 pcf.
We have increased the active soil pressure to 38 pcf, and the passive soil pressure
was reduced to 275 pcf. The calculated friction coefficient of 0.649 has been reduced
to an allowable value of 0.35.
VI. REGIONAL GEOLOGIC DESCRIPTION
San Diego County has been divided into three major geomorphic provinces: The
Coastal Plain, the Peninsular Ranges and the Salton Trough. The Coastal Plain exists
west of the Peninsular Ranges. The Salton Trough is east of the Peninsular Ranges.
These divisions are the result of the basic geologic distinctions between the areas.
Mesozoic metavolcanic, metasedimentary and plutonic rocks predominate in the
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Peninsular Ranges with primarily Cenozoic sedimentary rocks to the west and east of
this central mountain range (Demere, 1997).
In the Coastal Plain region, where the subject property is located, the “basement”
consists of Mesozoic crystalline rocks. Basement rocks are also exposed as high relief
areas (e.g., Black Mountain northeast of the subject property and Cowles Mountain
near the San Carlos area of San Diego). Younger Cretaceous and Tertiary sediments
lap up against these older features. These sediments form a “layer cake” sequence
of marine and non-marine sedimentary rock units, with some formations up to 140
million years old. Faulting related to the La Nación and Rose Canyon Fault zones has
broken up this sequence into a number of distinct fault blocks in the southwestern
part of the county. Northwestern portions of the county are relatively undeformed
by faulting (Demere, 1997).
The Peninsular Range form the granitic spine of San Diego County. These rocks are
primarily plutonic, forming at depth beneath the earth’s crust 140 to 90 million years
ago as the result of the subduction of an oceanic crustal plate beneath the North
American continent. These rocks formed the much larger Southern California
batholith. Metamorphism associated with the intrusion of these great granitic masses
affected the much older sediments that existed near the surface over that period of
time. These metasedimentary rocks remain as roof pendants of marble, schist, slate,
quartzite and gneiss throughout the Peninsular Ranges. Locally, Miocene-age
volcanic rocks and flows have also accumulated within these mountains (e.g.,
Jacumba Valley). Regional tectonic forces and erosion over time have uplifted and
unroofed these granitic rocks to expose them at the surface (Demere, 1997).
The Salton Trough is the northerly extension of the Gulf of California. This zone is
undergoing active deformation related to faulting along the Elsinore and San Jacinto
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Fault Zones, which are part of the major regional tectonic feature in the southwestern
portion of California, the San Andreas Fault Zone. Translational movement along
these fault zones has resulted in crustal rifting and subsidence. The Salton Trough,
also referred to as the Colorado Desert, has been filled with sediments to depth of
approximately 5 miles since the movement began in the early Miocene, 24 million
years ago. The source of these sediments has been the local mountains as well as
the ancestral and modern Colorado River (Demere, 1997).
As indicated previously, the San Diego area is part of a seismically active region of
California. It is on the eastern boundary of the Southern California Continental
Borderland, part of the Peninsular Ranges Geomorphic Province. This region is part
of a broad tectonic boundary between the North American and Pacific Plates. The
actual plate boundary is characterized by a complex system of active, major, right-
lateral strike-slip faults, trending northwest/southeast. This fault system extends
eastward to the San Andreas Fault (approximately 70 miles from San Diego) and
westward to the San Clemente Fault (approximately 50 miles off-shore from San
Diego) (Berger and Schug, 1991).
In California, major earthquakes can generally be correlated with movement on
active faults. As defined by the California Division of Mines and Geology, now the
California Geological Survey, an "active" fault is one that has had ground surface
displacement within Holocene time, about the last 11,000 years (Hart and Bryant,
1997). Additionally, faults along which major historical earthquakes have occurred
(about the last 210 years in California) are also considered to be active (Association
of Engineering Geologist, 1973). The California Division of Mines and Geology defines
a "potentially active" fault as one that has had ground surface displacement during
Quaternary time, that is, between 11,000 and 1.6 million years (Hart and Bryant,
1997).
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During recent history, prior to April 2010, the San Diego County area has been
relatively quiet seismically. No fault ruptures or major earthquakes had been
experienced in historic time within the greater San Diego area. Since earthquakes
have been recorded by instruments (since the 1930s), the San Diego area has
experienced scattered seismic events with Richter magnitudes generally less than
M4.0. During June 1985, a series of small earthquakes occurred beneath San Diego
Bay, three of which were recorded at M4.0 to M4.2. In addition, the Oceanside
earthquake of July 13, 1986, located approximately 26 miles offshore of the City of
Oceanside, had a magnitude of M5.3 (Hauksson and Jones, 1988).
On June 15, 2004, a M5.3 earthquake occurred approximately 45 miles southwest of
downtown San Diego (26 miles west of Rosarito, Mexico). Although this earthquake
was widely felt, no significant damage was reported. Another widely felt earthquake
on a distant southern California fault was a M5.4 event that took place on July 29,
2008, west-southwest of the Chino Hills area of Riverside County.
Several earthquakes ranging from M5.0 to M6.0 occurred in northern Baja California,
centered in the Gulf of California on August 3, 2009. These were felt in San Diego
but no injuries or damage was reported. A M5.8 earthquake followed by a M4.9
aftershock occurred on December 30, 2009, centered about 20 miles south of the
Mexican border city of Mexicali. These were also felt in San Diego, swaying high-rise
buildings, but again no significant damage or injuries were reported.
On April 4, 2010, a large earthquake occurred in Baja California, Mexico. It was
widely felt throughout the southwest including Phoenix, Arizona and San Diego in
California. This M7.2 event, the Sierra El Mayor earthquake, occurred in northern
Baja California, approximately 40 miles south of the Mexico-USA border at shallow
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depth along the principal plate boundary between the North American and Pacific
plates. According to the U. S. Geological Survey this is an area with a high level of
historical seismicity, and it has recently also been seismically active, although this is
the largest event to strike in this area since 1892. The April 4, 2010, earthquake
appears to have been larger than the M6.9 earthquake in 1940 or any of the early
20th century events (e.g., 1915 and 1934) in this region of northern Baja California.
The event caused widespread damage to structures, closure of businesses,
government offices and schools, power outages, displacement of people from their
homes and injuries in the nearby major metropolitan areas of Mexicali in Mexico and
Calexico in Southern California.
This event's aftershock zone extends significantly to the northwest, overlapping with
the portion of the fault system that is thought to have ruptured in 1892. Some
structures in the San Diego area experienced minor damage and there were some
injuries. Ground motions for the April 4, 2010, main event, recorded at stations in
San Diego and reported by the California Strong Motion Instrumentation Program
(CSMIP), ranged up to 0.058g.
On July 7, 2010, a M5.4 earthquake occurred in Southern California at 4:53 pm
(Pacific Time) about 30 miles south of Palm Springs, 25 miles southwest of Indio, and
13 miles north-northwest of Borrego Springs. The earthquake occurred near the
Coyote Creek segment of the San Jacinto Fault. The earthquake exhibited right
lateral slip to the northwest, consistent with the direction of movement on the San
Jacinto Fault. The earthquake was felt throughout Southern California, with strong
shaking near the epicenter. It was followed by more than 60 aftershocks of M1.3
and greater during the first hour.
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In the last 50 years, there have been four other earthquakes in the magnitude M5.0
range within 20 kilometers of the Coyote Creek segment: M5.8 in 1968, M5.3 on
2/25/1980, M5.0 on 10/31/2001, and M5.2 on 6/12/2005. The biggest earthquake
near this location was the M6.0 Buck Ridge earthquake on 3/25/1937.
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION
Our field investigation, reconnaissance and review of the geologic map by Kennedy
and Tan, 2007, “Geologic Map of the Oceanside 30’x60’ Quadrangle, California”
indicate that the site is underlain at depth by late to middle Pleistocene-Aged Old
Paralic Deposits, Units 6-7 (Qop6-7) formational materials. An excerpt of the
geological map is included as Figure No. V. Our exploratory trenches indicate the
formational materials are overlain across the site by artificial fill soils (Qaf) and
subsoil/residual soil. Site-specific geology is mapped on Figure No. II, the Plot Plan.
Fill Soil (Qaf): Our site investigation indicates that the areas in the general vicinity
of our exploratory trenches at the site are overlain by up to 12-inches of fill soil. The
encountered fill soil consists of fine- to medium-grained, dry to moist, gray-brown to
red-brown to brown, silty sands (SM) with variable amounts of roots. The fill soils
are generally loose. In our opinion, due to the variable density and poor condition of
the fill soil, it is not considered suitable in its current condition to support loads from
structures or additional fill. Refer to Figure Nos. IIIa-e for details.
Residual Soil/Subsoil: Residual/Subsoil was encountered underlying the fill soils in
all the exploratory trenches. The approximate thickness of these soils was observed
to vary from approximately 0.5 to 3 feet in thickness. These soils were noted to
consist mainly of damp, light-brown, silty sands (SM). This material was observed
to be generally loose to medium dense, porous and with some deeper roots. In our
opinion, due to the low density and potential compressibility of these porous soils,
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these residual soils are not considered suitable to support loads from structures or
additional fill in their current condition. Refer to Figure Nos. IIIa-e for details.
Old Paralic Deposits, Unit 6-7 (Qop6-7): The encountered formational materials are
described in the literature as Quaternary (late to middle Pleistocene Old Paralic
Deposits, Units 6-7. These formational materials were encountered in all trenches
underlying the residual soil at variable depths from 1.0 to 2.5 feet. The formational
materials consist of fine- to medium-grained, damp to moist, red-brown silty sands
(SM) with areas of moderate cementation and some deeper roots. The formational
materials underlying the site are dense to very dense. In our opinion, the dense to
very dense nature of the Old Paralic Deposits, Units 6-7, makes it suitable in its
current condition to support loads from structures or additional fill. Refer to Figure
Nos. IIIa-e for details.
Based on our review of the geologic map by Kennedy and Tan, 2007, “Geologic Map
of the Oceanside 30’x60’ Quadrangle, California” the Old Paralic Deposits, Units 6-7,
formational materials underlie the entire site at depth. The aforementioned Old
Paralic Deposit Units are described as “Poorly sorted, moderately permeable, reddish-
brown, interfingered strandline, beach, estuarine and colluvial deposits composed of
siltstone, sandstone and conglomerate.” According to the map, there are no faults
known to pass through the site (refer to Figure No. V, Geologic Map Excerpt and
Legend).
VIII. GEOLOGIC HAZARDS
The following is a discussion of the geologic conditions and hazards common to this
area of Carlsbad, as well as project-specific geologic information relating to
development of the subject site.
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A. Local and Regional Faults
Reference to the Geologic Map and Legend, Figure No. V (Kennedy and Tan, 2007),
indicates that no faults are shown to cross the site. Furthermore, our site
reconnaissance presented no indications of faulting crossing the site. In our
professional opinion, neither an active fault nor a potentially active fault underlies
the site.
A brief description of the nearby active faults including distances from the mapped
fault to the subject site at the closest point (based on the USGS Earthquake Hazards-
Interactive Fault Map), is presented below:
Newport-Inglewood-Rose Canyon Fault Zone System: The Oceanside section of the
Newport-Inglewood-Rose Canyon Fault Zone is mapped approximately 4.3 miles
west-southwest of the site. The offshore portion of the Newport-Inglewood Fault
Zone is described as a right-lateral; local reverse slip associated with fault steps
(SCEDC, 2020); the reported length is 46.2 miles extending in a northwest-southeast
direction. Surface trace is discontinuous in the Los Angeles Basin, but the fault zone
can easily be noted there by the existence of a chain of low hills extending from
Culver City to Signal Hill. South of Signal Hill, it roughly parallels the coastline until
just south of Newport Bay, where it heads offshore, and becomes the Newport-
Inglewood - Rose Canyon Fault Zone. A significant earthquake (M6.4) occurred along
this fault on March 10, 1933. Since then, no additional significant events have
occurred. The fault is believed to have a slip rate of approximately 0.6-mm/yr with
an unknown recurrence interval. This fault is believed capable of producing an
earthquake of M6.0 to M7.4 (Grant Ludwig and Shearer, 2004).
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Rose Canyon Fault Zone: The Rose Canyon Fault Zone is the southern section of the
Newport-Inglewood-Rose Canyon Fault Zone system mapped in the San Diego
County area as trending north-northwest to south-southeast from Oceanside to La
Jolla and generally north-south into San Diego Bay, through Coronado and offshore
downtown San Diego, from where it appears to head southward. The Rose Canyon
Fault Zone system is considered to be a complex zone of onshore and offshore, en
echelon right lateral, strike slip, oblique reverse, and oblique normal faults. This fault
is considered to be capable of generating an M7.2 earthquake and is considered
microseismically active, although no significant recent earthquakes since 1769 are
known to have occurred on the fault.
Investigative work on faults that are part of the Rose Canyon Fault Zone at the Police
Administration and Technical Center in downtown San Diego, at the SDG&E facility in
Rose Canyon, and within San Diego Bay and elsewhere within downtown San Diego,
has encountered offsets in Holocene (geologically recent) sediments. These findings
confirm Holocene displacement on the Rose Canyon Fault, which was designated an
“active” fault in November 1991 (Hart and Bryant, 1997).
Rockwell (2010) has suggested that the Rose CFZ underwent a cluster of activity
including 5 major earthquakes in the early Holocene, with a long period of inactivity
following, suggesting major earthquakes on the RCFZ behaves in a cluster-mode,
where earthquake recurrence is clustered in time rather than in a consistent
recurrence interval. With the most recent earthquake (MRE) nearly 500 years ago,
it is suggested that a period of earthquake activity on the RCFZ may have begun.
Rockwell (2010) and a compilation of the latest research implies a long-term slip rate
of approximately 1 to 2 mm/year.
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Coronado Bank Fault: The Coronado Bank Fault is located approximately 22.6 miles
southwest of the site. Evidence for this fault is based upon geophysical data (acoustic
profiles) and the general alignment of epicenters of recorded seismic activity (Greene
et al., 1979). The Oceanside earthquake of M5.3 recorded July 13, 1986, is known
to have been centered on the fault or within the Coronado Bank Fault Zone. Although
this fault is considered active, due to the seismicity within the fault zone, it is
significantly less active seismically than the Elsinore Fault (Hileman et al., 1973). It
is postulated that the Coronado Bank Fault is capable of generating a M7.6
earthquake and is of great interest due to its close proximity to the greater San Diego
metropolitan area.
San Diego Trough Fault Zone: The San Diego Through Fault Zone is mapped at
approximately 29.6 miles to the west-southwest of the site at its closest point. This
fault is described as a right-lateral type fault with a length of at least 93.2 miles and
a slip rate of roughly 1.5 mm/yr. The most recent surface rupture is of Holocene age
(SCEDC, 2020).
San Clemente Fault Zone: The San Clemente Fault Zone is mapped at approximately
56 miles to the southwest of the site at its closest point. This fault is described as a
right-lateral and vertical offsets type fault with a length of at least 130.5 miles
described as essentially continuous with the San Isidro fault zone, off the coast of
Mexico and a slip rate of roughly 1.5 mm/yr. The most recent surface rupture is of
Holocene age (SCEDC, 2020).
Elsinore Fault: The Temecula and Julian sections of the Elsinore Fault Zone are
located approximately 23.5 and 33 miles northeast and east of the site respectively.
The Elsinore Fault Zone extends approximately 125 miles from the Mexican border
to the northern end of the Santa Ana Mountains. The Elsinore Fault zone is a 1- to
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4-mile-wide, northwest-southeast-trending zone of discontinuous and en echelon
faults extending through portions of Orange, Riverside, San Diego, and Imperial
Counties. Individual faults within the Elsinore Fault Zone range from less than 1 mile
to 16 miles in length. The trend, length and geomorphic expression of the Elsinore
Fault Zone identify it as being a part of the highly active San Andreas Fault system.
Like the other faults in the San Andreas system, the Elsinore Fault is a transverse
fault showing predominantly right-lateral movement. According to Hart et al. (1979),
this movement averages less than 1 centimeter per year. Along most of its length,
the Elsinore Fault Zone is marked by a bold topographic expression consisting of
linearly aligned ridges, swales and hallows. Faulted Holocene alluvial deposits
(believed to be less than 11,000 years old) found along several segments of the fault
zone suggest that at least part of the zone is currently active.
Although the Elsinore Fault Zone belongs to the San Andreas set of active, northwest-
trending, right-slip faults in the southern California area (Crowell, 1962), it has not
been the site of a major earthquake in historic time, other than a M6.0 earthquake
near the town of Elsinore in 1910 (Richter, 1958; Toppozada and Parke, 1982).
However, based on length and evidence of late-Pleistocene or Holocene displacement,
Greensfelder (1974) has estimated that the Elsinore Fault Zone is reasonably capable
of generating an earthquake with a magnitude as large as M7.5. Study and logging
of exposures in trenches placed in Glen Ivy Marsh across the Glen Ivy North Fault (a
strand of the Elsinore Fault Zone between Corona and Lake Elsinore), suggest a
maximum earthquake recurrence interval of 300 years, and when combined with
previous estimates of the long-term horizontal slip rate of 0.8 to 7.0 mm/year,
suggest typical earthquake magnitudes of M6.0 to M7.0 (Rockwell et al., 1985). The
Working Group on California Earthquake Probabilities (2008) has estimated that there
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is a 11 percent probability that an earthquake of M6.7 or greater will occur within 30
years on this fault.
San Jacinto Fault: The San Jacinto Fault is located approximately 46 to 66 miles
northeast of the site. The San Jacinto Fault Zone consists of a series of closely spaced
faults, including the Coyote Creek Fault, that form the western margin of the San
Jacinto Mountains. The fault zone extends from its junction with the San Andreas
Fault in San Bernardino, southeasterly toward the Brawley area, where it continues
south of the international border as the Imperial Transform Fault (Rockwell et al.,
2014).
The San Jacinto Fault zone has a high level of historical seismic activity, with at least
10 damaging earthquakes (M6.0 to M7.0) having occurred on this fault zone between
1890 and 1986. Earthquakes on the San Jacinto Fault in 1899 and 1918 caused
fatalities in the Riverside County area. Offset across this fault is predominantly right-
lateral, similar to the San Andreas Fault, although some investigators have suggested
that dip-slip motion contributes up to 10% of the net slip (Ross et al., 2017).
The segments of the San Jacinto Fault that are of most concern to major metropolitan
areas are the San Bernardino, San Jacinto Valley and Anza segments. Fault slip rates
on the various segments of the San Jacinto are less well constrained than for the San
Andreas Fault, but the available data suggest slip rates of 12 ±6 mm/yr for the
northern segments of the fault, and slip rates of 4 ±2 mm/yr for the southern
segments. For large ground-rupturing earthquakes on the San Jacinto fault, various
investigators have suggested a recurrence interval of 150 to 300 years. The Working
Group on California Earthquake Probabilities (2008) has estimated that there is a 31
percent probability that an earthquake of M6.7 or greater will occur within 30 years
on this fault. Maximum credible earthquakes of M6.7, M6.9 and M7.2 are expected
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on the San Bernardino, San Jacinto Valley and Anza segments, respectively, capable
of generating peak horizontal ground accelerations of 0.48g to 0.53g in the County
of Riverside. A M5.4 earthquake occurred on the San Jacinto Fault on July 7, 2010.
The United States Geological Survey has issued the following statements with respect
to the recent seismic activity on southern California faults:
The San Jacinto fault, along with the Elsinore, San Andreas, and other
faults, is part of the plate boundary that accommodates about 2
inches/year of motion as the Pacific plate moves northwest relative to
the North American plate. The largest recent earthquake on the San
Jacinto fault, near this location, the M6.5 1968 Borrego Mountain
earthquake April 8, 1968, occurred about 25 miles southeast of the July
7, 2010, M5.4 earthquake. This M5.4 earthquake follows the 4th of April
2010, Easter Sunday, M7.2 earthquake, located about 125 miles to the
south, well south of the US Mexico international border. A M4.9
earthquake occurred in the same area on June 12th at 8:08 pm (Pacific
Time). Thus, this section of the San Jacinto fault remains active.
Seismologists are watching two major earthquake faults in southern
California. The San Jacinto fault, the most active earthquake fault in
southern California, extends for more than 100 miles from the
international border into San Bernardino and Riverside, a major
metropolitan area often called the Inland Empire. The Elsinore fault is
more than 110 miles long, and extends into the Orange County and Los
Angeles area as the Whittier fault. The Elsinore fault is capable of a
major earthquake that would significantly affect the large metropolitan
areas of southern California. The Elsinore fault has not hosted a major
earthquake in more than 100 years. The occurrence of these
earthquakes along the San Jacinto fault and continued aftershocks
demonstrates that the earthquake activity in the region remains at an
elevated level. The San Jacinto fault is known as the most active
earthquake fault in southern California. Caltech and USGS seismologist
continue to monitor the ongoing earthquake activity using the
Caltech/USGS Southern California Seismic Network and a GPS network
of more than 100 stations.
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B. Other Geologic Hazards
Ground Rupture: Ground rupture is characterized by bedrock slippage along an
established fault and may result in displacement of the ground surface. For ground
rupture to occur along a fault, an earthquake usually exceeds M5.0. If a M5.0
earthquake were to take place on a local fault, an estimated surface-rupture length
1 mile long could be expected (Greensfelder, 1974). Our investigation indicates that
the subject site is not directly on a known active fault trace and, therefore, the risk
of ground rupture is remote.
Ground Shaking: Structural damage caused by seismically induced ground shaking
is a detrimental effect directly related to faulting and earthquake activity. Ground
shaking is considered to be the greatest seismic hazard in San Diego County. The
intensity of ground shaking is dependent on the magnitude of the earthquake, the
distance from the earthquake, and the seismic response characteristics of underlying
soils and geologic units. Earthquakes of M5.0 or greater are generally associated
with significant damage. It is our opinion that the most serious damage to the site
would be caused by a large earthquake originating on a nearby strand of the Rose
Canyon, Coronado Bank or Newport-Inglewood Faults. Although the chance of such
an event is remote, it could occur within the useful life of the structure.
Landslides: Our investigation indicates that the subject site is not directly on a known
recent or ancient landslide. Review of the “Geologic Map of the Oceanside 30’x60’
Quadrangle, California” by Kennedy and Tan (2007) and the USGS Landslide Hazard
Program Site (US Landslide Inventory), indicate that there are no known or suspected
ancient landslides located on the site.
Slope Stability: Our site reconnaissance indicates that the site slopes gently in an
eastern direction, with only an 8-foot difference in elevation across the area of the
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site. The site is underlain by relatively stable and dense Old Paralic Deposits, Unit 6-
7 formational materials at a depth of 1.0 to 3.0 feet. In our opinion, there is not a
slope stability issue with the site.
Liquefaction: The liquefaction of saturated sands during earthquakes can be a major
cause of damage to buildings. Liquefaction is the process by which soils are
transformed into a viscous fluid that will flow as a liquid when unconfined. It occurs
primarily in loose, cohesionless saturated silt, sand, and fine-grained gravel deposits
of Holocene to late Pleistocene age and in areas where the groundwater is shallower
than about 50 feet (DMG Special Publication 117) when they are sufficiently shaken
by an earthquake. On this site, the risk of liquefaction of formational materials due
to seismic shaking is considered to be very low due to the dense to very dense nature
of the underlying formational materials and the lack of shallow static groundwater.
The site does not have a potential for soil strength loss to occur due to a seismic
event.
Tsunamis and Seiches: A tsunami is a series of long waves generated in the ocean
by a sudden displacement of a large volume of water. Underwater earthquakes,
landslides, volcanic eruptions, meteor impacts, or onshore slope failures can cause
this displacement. Tsunami waves can travel at speeds averaging 450 to 600 miles
per hour. As a tsunami nears the coastline, its speed diminishes, its wave length
decreases, and its height increases greatly. After a major earthquake or other
tsunami-inducing activity occurs, a tsunami could reach the shore within a few
minutes. One coastal community may experience no damaging waves while another
may experience very destructive waves. Some low-lying areas could experience
severe inland inundation of water and deposition of debris more than 3,000 feet
inland.
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The site is located approximately 0.17-mile from the exposed coastline and at an
elevation of approximately 59 to 67 feet above MSL. Review of the Tsunami
Inundation Map for Emergency Planning, Encinitas Quadrangle, the site is located
outside the inundation area. There is no risk of tsunami inundation at the site.
A seiche is a run-up of water within a lake or embayment triggered by fault- or
landslide-induced ground displacement. The site is located near a coastal lagoon,
that is not considered capable of producing a seiche and inundating the subject site.
Flood Hazard: Review of the FEMA flood maps number 06073C0764H, effective on
12/20/2019, the project site is located within the Special Flood Hazard Area (SFHA)
X. Zone X is described as minimal flood hazard. The civil engineer should verify this
statement with the City of Carlsbad and County of San Diego (FEMA, 2019).
Geologic Hazards Summary: It is our opinion, based upon a review of the available
maps, our research and our site investigation, that the site is underlain at shallow
depth by stable Old Paralic Deposits formational materials and is suited for the
proposed residential structures. retaining walls and associated improvements
provided the recommendations herein are implemented. Furthermore, based on the
available information at this stage, it appears the proposed site development will not
destabilize or result in settlement of adjacent property or improvements if the
recommendations presented in this report are implemented.
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No significant geologic hazards are known to exist on the site that would prohibit the
construction of the proposed residential structures, retaining walls and associated
improvements. Ground shaking from earthquakes on active southern California faults
and active faults in northwestern Mexico is the greatest geologic hazard at the
property. Design of building structures in accordance with the current building codes
would reduce the potential for injury or loss of human life. Buildings constructed in
accordance with current building codes may suffer significant damage but should not
undergo total collapse.
In our explicit professional opinion, no active or potentially active faults underlie the
project site.
IX. GROUNDWATER
Free groundwater was not encountered in our exploratory excavations to the
maximum depths explored. A more detailed description of the subsurface materials
encountered in our exploratory excavations Figure Nos. IIIa-e.
It should also be recognized that minor groundwater seepage problems might occur
after development of a site even where none were present before development.
These are usually minor phenomena and are often the result of an alteration in
drainage patterns and/or an increase in irrigation water. Based on the permeability
characteristics of the soil and the anticipated usage and development, it is our opinion
that any seepage problems, which may occur, will be minor in extent. It is further
our opinion that these problems can be most effectively corrected on an individual
basis if and when they occur.
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We do not anticipate significant groundwater problems to develop in the future, if the
property is developed as proposed and proper drainage is implemented and
maintained.
It should be kept in mind that any required construction operations will change
surface drainage patterns and/or reduce permeabilities due to the densification of
compacted soils. Such changes of surface and subsurface hydrologic conditions, plus
irrigation of landscaping or significant increases in rainfall, may result in the
appearance of surface or near-surface water at locations where none existed
previously. The damage from such water is expected to be localized and cosmetic in
nature, if good positive drainage is implemented, as recommended in this report,
during and at the completion of construction.
On properties such as the subject site where dense, low permeability soils exist at
shallow depths, even normal landscape irrigation practices on the property or
neighboring properties, or periods of extended rainfall, can result in shallow
“perched” water conditions. The perching (shallow depth) accumulation of water on
a low permeability surface can result in areas of persistent wetting and drowning of
lawns, plants and trees. Resolution of such conditions, should they occur, may
require site-specific design and construction of subdrain and shallow “wick” drain
dewatering systems.
Subsurface drainage with a properly designed and constructed subdrain system will
be required along with continuous back drainage behind any proposed lower-level
basement walls, property line retaining walls, or any perimeter stem walls for raised-
wood floors where the outside grades are higher than the crawl space grades.
Furthermore, crawl spaces, if used, should be provided with the proper cross-
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ventilation to help reduce the potential for moisture-related problems. Additional
recommendations may be required at the time of construction.
It must be understood that unless discovered during site exploration or encountered
during site construction operations, it is extremely difficult to predict if or where
perched or true groundwater conditions may appear in the future. When site fill or
formational soils are fine-grained and of low permeability, water problems may not
become apparent for extended periods of time.
Water conditions, where suspected or encountered during construction, should be
evaluated and remedied by the project civil and geotechnical consultants. The project
developer and property owner, however, must realize that post-construction
appearances of groundwater may have to be dealt with on a site-specific basis.
Proper functional surface drainage should be implemented and maintained at the
property.
X. CONCLUSIONS & RECOMMENDATIONS
The following recommendations are based upon the practical field investigations
conducted by our firm, and resulting laboratory tests, in conjunction with our
knowledge and experience with similar soils in the Carlsbad area. The opinions,
conclusions, and recommendations presented in this report are contingent upon
Geotechnical Exploration, Inc. being retained to review the final plans and
specifications as they are developed and to observe the site earthwork and
installation of foundations. Accordingly, we recommend that the following paragraph
be included on the grading and foundation plans for the project.
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If the geotechnical consultant of record is changed for the project, the
work shall be stopped until the replacement has agreed in writing to
accept responsibility within their area of technical competence for
approval upon completion of the work. It shall be the responsibility of
the permittee to notify the governing agency in writing of such change
prior to the recommencement of grading and/or foundation installation
work and comply with the governing agency’s requirements for a change
to the Geotechnical Consultant of Record for the project.
We recommend that the planned residential structures, garages and retaining walls
be supported by conventional, individual-spread and/or continuous footing
foundations founded on medium dense to dense formational soils and minimum 90
percent compacted structural fill soils. Individual structures may bear on dense
formational or fill soils depending on their locations, final grading elevations and
exposure of formational materials.
Existing fill soils across the entire site will be disturbed during the demolition of the
existing structures, and are not suitable in their current condition to support new
structures or associated improvements. A full removal and recompaction of existing
fill and residual soils across the site will be required to support the proposed
structures and associated improvements. Fill soils across the site will be required to
be compacted to at least 90 percent relative compaction. Existing fill soil and
formational materials are suitable for use as recompacted fill soils. Any buried trash
and roots encountered during site demolition and fill soil recompaction should be
removed and exported off site.
It is our opinion that the site is suitable for the planned residential project provided
the recommendations herein are incorporated during design and construction.
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A. Preparation of Soils for Site Development
1. General: Grading should conform to the guidelines presented in the 2019
California Building Code (CBC, 2019), as well as the requirements of the City
of Carlsbad.
During earthwork construction, removals and reprocessing of fill materials, as
well as general grading procedures of the contractor should be observed and
the fill placed selectively tested by representatives of the geotechnical
engineer, Geotechnical Exploration Inc. If any unusual or unexpected
conditions are exposed in the field, they should be reviewed by the
geotechnical engineer and if warranted, modified and/or additional remedial
recommendations will be offered. Specific guidelines and comments pertinent
to the planned development are provided herein.
The recommendations presented herein have been completed using the
information provided to us regarding site development. If information
concerning the proposed development is revised, or any changes in the design
and location of the proposed property modified or approved in writing by this
office.
2. Clearing and Stripping: Complete demolition of the existing residential
structure and associated improvements should be undertaken. This is to
include the complete removal of all subsurface footings, utility lines and
miscellaneous debris. After clearing the entire ground surface of the site
should be stripped of existing vegetation within the areas of proposed new
construction. This includes any roots from existing trees and shrubbery. Holes
resulting from the removal of root systems or other buried obstructions that
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extend below the planned grades should be cleared and backfilled with suitable
compacted material compacted to the requirements provided under
Recommendation Nos. 3, 4 and 5 below. Prior to any filling operations, the
cleared and stripped vegetation and debris should be disposed of off-site.
3. Excavation: After the entire site has been cleared and stripped, all of the
existing fill soils and topsoil should be removed and recompacted. The depth
of removals across the site will vary depending on the thickness of unsuitable
soils overlying the formational materials. It is anticipated that the depth of
removals will be at least 3 feet below existing grade in the area of the existing
house pad, however, shallower removals (at least 2 feet) may be anticipated
across the remainder of the site. Based on the results of our exploratory
trenches and test holes, as well as our experience with similar materials in the
project area, it is our opinion that the existing fill soils and topsoil materials
can be excavated utilizing ordinary light to heavy weight earthmoving
equipment. Contractors should not, however, be relieved of making their own
independent evaluation of excavating the on-site materials prior to submitting
their bids. Contractors should also review this report along with the trench
logs to understand the scope and quantity of grading required for this project.
Variability in excavating the subsurface materials should be expected across
the project area.
The areal extent required to remove the surficial soils should be confirmed by
our representatives during the excavation work based on their examination of
the soils being exposed. The lateral extent of the excavation and recompaction
should be at least 5 feet beyond the edge of the perimeter ground level
foundations of the new residential structure and any areas to receive exterior
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improvements, or fill slopes, where feasible, or to the depth of excavation or
fill at that location, whichever is greater.
4. Cut-Fill Transition: Based on the review of the preliminary survey plans it
appears that the new residential structure may be planned to be constructed
on a cut-fill transition line.
New structures should not bear on a cut-fill transition line. If a cut-fill
transition line exists within the proposed building envelope, we recommend
that the cut portion of the building pad, be undercut to a minimum of 24 inches
below the bottom of the proposed footing depth. The bottom of the over
excavation should be observed and approved by a representative of
Geotechnical Exploration Inc., to verify that all loose and unsuitable soils
have been completely removed prior to reprocessing. After approval, the
bottom of the excavation should be scarified to a minimum depth of 8 inches
below removal grade elevations, brought to near-optimum moisture conditions
and recompacted to at least 90 percent relative compaction (based on ASTM
Test Method D1557). Backfill and compaction of the remaining structural fill
should be performed based on the recommendations presented in the following
sections. No structures should be supported on a building pad with structural
fill soil thickness differential of greater than 5 feet.
5. Subgrade Preparation: After the site has been cleared, stripped, and the
required excavations made, the exposed subgrade soils in areas to receive new
fill and/or slab-on-grade building improvements should be scarified to a depth
of 6 inches, moisture conditioned, and compacted to the requirements for
structural fill. While not anticipated, in the event that planned cuts expose any
medium to highly expansive formational materials in the building areas, they
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should be scarified and moisture conditioned to at least 3 percent over
optimum moisture for low expansive soils and 5 percent for medium and highly
expansive soils (if encountered).
6. Material for Fill: Existing on-site low-expansion potential (Expansion Index of
50 or less per ASTM D4829-19) soils with an organic content of less than 3
percent by volume are, in general, suitable for use as fill. Imported fill
material, where required, should have a low-expansion potential. In addition,
both imported and existing on-site materials for use as fill should not contain
rocks or lumps more than 6 inches in greatest dimension if the fill soils are
compacted with heavy compaction equipment (or 3 inches in greatest
dimension if compacted with lightweight equipment). All materials for use as
fill should be approved by our representative prior to importing to the site.
If encountered at the site, medium to highly expansive soils should not be used
as structural fill at a depth of less than 5 feet from footing bearing surface
elevation or behind retaining walls. Backfill material to be placed behind
retaining walls should be low expansive (E.I. less than 50), with rocks no larger
than 3 inches in diameter.
7. Structural Fill Compaction: All structural fill, and areas to receive any
associated improvements, should be compacted to a minimum degree of
compaction of 90 percent based upon ASTM D1557-12e1. Fill material should
be spread and compacted in uniform horizontal lifts not exceeding 8 inches in
uncompacted thickness. Before compaction begins, the fill should be brought
to a water content that will permit proper compaction by either: (1) aerating
and drying the fill if it is too wet, or (2) watering the fill if it is too dry. Each
lift should be thoroughly mixed before compaction to ensure a uniform
distribution of moisture. For low expansive soils, the moisture content should
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be within 2 percent of optimum. Though we do not anticipate any medium to
high expansive soils to be exposed during grading operations, if encountered,
the compaction moisture content should be at least 5 percent over optimum.
Any rigid improvements founded on the existing undocumented fill soils can
be expected to undergo movement and possible damage. Geotechnical
Exploration, Inc. takes no responsibility for the performance of any
improvements built on loose natural soils or inadequately compacted fills.
Subgrade soils in any exterior area receiving concrete improvements should
be verified for compaction and moisture by a representative of our firm within
48 hours prior to concrete placement.
No uncontrolled fill soils should remain after completion of the site work. In
the event that temporary ramps or pads are constructed of uncontrolled fill
soils, the loose fill soils should be removed and/or recompacted prior to
completion of the grading operation. Based on the results of our laboratory
testing (see Section V above), the water-soluble sulfate content of the tested
soils at the site yielded a negligible sulfate exposure, as such based on table
1904.3 of the building code, there is no restrictions for cement type.
8. Trench and Retaining Wall Backfill: All utility trenches and retaining walls
should be backfilled with properly compacted fill. Backfill material should be
placed in lift thicknesses appropriate to the type of compaction equipment
utilized and compacted to a minimum degree of compaction of 90 percent
based upon ASTM D1557-12e1 by mechanical means. Any portion of the
trench backfill in public street areas within pavement sections should conform
to the material and compaction requirements of the adjacent pavement
section.
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Backfill soils placed behind retaining walls should be installed as early as the
retaining walls are capable of supporting lateral loads. Backfill soils behind
retaining walls should be low expansive (Expansion Index less than 50 per
ASTM D4829-19).
Our experience has shown that even shallow, narrow trenches (such as for
irrigation and electrical lines) that are not properly compacted can result in
problems, particularly with respect to shallow groundwater accumulation and
migration.
9. Observations and Testing: As stated in CBC 2019, Section 1705.6 Soils:
“Special inspections and tests of existing site soil conditions, fill placement and
load-bearing requirements shall be performed in accordance with this section
and Table 1705.6 (see below). The approved geotechnical report and the
construction documents prepared by the registered design professionals shall
be used to determine compliance. During fill placement, the special inspector
shall verify that proper materials and procedures are used in accordance with
the provisions of the approved geotechnical report”.
A summary of Table 1705.6 “REQUIRED SPECIAL INSPECTIONS AND TESTS
OF SOILS” is presented below:
a) Verify materials below shallow foundations are adequate to achieve the
design bearing capacity;
b) Verify excavations are extended to proper depth and have reached
proper material;
c) Perform classification and testing of compacted fill materials;
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d) Verify use of proper materials, densities and thicknesses during
placement and compaction of compacted fill prior to placement of compacted
fill, inspect subgrade and verify that site has been prepared properly
Section 1705.6 “Soils” statement and Table 1705.6 indicate that it is
mandatory that a representative of this firm (responsible engineering firm),
perform observations and fill compaction testing during excavation operations
to verify that the remedial operations are consistent with the recommendations
presented in this report. All grading excavations resulting from the removal
of soils should be observed and evaluated by a representative of our firm
before they are backfilled.
Quality control grading observation and field density testing for the purpose of
documenting that adequate compaction has been achieved and acceptable
soils have been utilized to properly support a project applies not only to fill
soils supporting primary structures; unless supported by deep foundations or
caissons, but all site improvements such as stairways, patios, pools and pool
decking, sidewalks, driveways and retaining walls etc. Observation and testing
of utility line trench backfill also reduces the potential for localized settlement
of all of the above including all improvements outside of the footprint of
primary structures.
Often after primary building pad grading, it is not uncommon for the
geotechnical engineer of record to not be notified of grading performed outside
the footprint of the project primary structures. As a result, settlement damage
of site improvements such as patios, pool and pool decks, exterior landscape
walls and walks, and structure access stairways can occur. It is therefore
strongly recommended that the project general contractor, grading contractor,
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and others tasked with completing a project with workmanship that reduces
the potential for damage to the project from soil settlement, or expansive soil
uplift, to be advised and acknowledge the importance of adequate and
comprehensive observation and testing of soils intended to support the project
they are working on. The project geotechnical engineers of record must be
contacted and requested to provide these services.
Failure to comply with this recommendation can result in several costly and
time-consuming requirements from the governing municipality or county
engineering and planning departments. For example, the geotechnical and/or
civil engineer of record may be required to:
• Clarify if observation and testing services were performed for all grading
shown on the Grading Plans. If not, indicate the areas NOT observed or
tested on the As-Graded Geological Map.
• A construction change must be processed to indicate the revised grading
recommendations by the geotechnical engineer of work on the plans.
• The geotechnical engineer must submit on addendum letter addressing
the change to the grading plan specifications for the earthwork
presented on the grading plans.
• The geotechnical consultant must evaluate the existing
unobserved/undocumented fill as an uncontrolled embankment and
provide a statement indicating the uncontrolled embankment will not
endanger the public health, safety and welfare. In order to make this
statement the geotechnical engineer would have to clearly define the
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potential problems such as damage to project improvements that could
result from construction on undocumented fill soils.
• The geotechnical consultant must indicate if the unobserved fill placed
during earthwork within the limits of work is suitable for the intended
use. To render such an opinion the geotechnical consultant would have
to place a sufficient number of test excavations and conduct enough
testing to warrant such an opinion.
• If the geotechnical consultant cannot render an opinion that the
unobserved fill is suitable for the purpose intended, “They must indicate
if additional fill remedial grading is recommended.”
• The limits of the “Unobserved fill/uncontrolled embankment must be
shown on revised grading plans along with the “Uncontrolled
Embankment Maintenance Agreement Approval Number.”
• The owner must execute an “Uncontrolled Embankment Agreement: for
the portion of the undocumented fill to remain. This must be
coordinated with the LDR Drainage and Grading reviewer.
• The title and date of the requested addendum letter or geotechnical
investigation report must be added under note no. 1 of the “Grading and
Geotechnical Specification” Certification as construction change “A”.
• These changes must be made on a redline copy, and submitted as a
“Construction Change A” for review and approval by the geology section
and Drainage and Grades Section.
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• All approved changes will then be transferred to the mylars for approval
and signatures by the Deputy City Engineer.
The Geotechnical Engineer of Record, in this case Geotechnical
Exploration, Inc., cannot be held responsible for the costs and time
delays associated with the lack of contact and requests for testing
services by the client, general contractor, grading contractor or any of
the project design team responsible for requesting the required
geotechnical services. Requests for services are to be made through
our office telephone number (858) 549-7222 and the telephone number
of the G.E.I. personnel assigned to the project.
B. Seismic Design Criteria
10. Seismic Data Bases: The estimation of the peak ground acceleration and the
repeatable high ground acceleration (RHGA) likely to occur at the site is based
on the known significant local and regional faults within 100 miles of the site.
11. Seismic Design Criteria: The proposed structure should be designed in
accordance with the 2019 CBC, which incorporates by reference the ASCE 7-
16 for seismic design. We have determined the mapped spectral acceleration
values for the site based on a latitude of 33.1550 degrees and a longitude
of -117.3357 degrees, utilizing a program titled “Seismic Design Map Tool” and
provided by the USGS through SEAOC, which provides a solution for ASCE 7-
16 utilizing digitized files for the Spectral Acceleration maps. See Appendix B.
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12. Structure and Foundation Design: The design of the new structures and
foundations should be based on Seismic Design Category D, Risk Category II
for a Site Class Stiff Soils D.
13. Spectral Acceleration and Design Values: The structural seismic design, when
applicable, should be based on the following values, which are based on the
site location, soil characteristics, and seismic maps by USGS, as required by
the 2019 CBC. The summarized seismic soil parameters are presented in table
I below, have been calculated with the SEAOC Seismic Design Map Tool. The
complete values are included in Appendix B. The Site Class Stiff Soil D values
for this property are:
TABLE I
Mapped Spectral Acceleration Values and Design Parameters
SS S1 SMS SM1 SDS SD1 Fa Fv PGA PGAM SDC
1.098 0.396 1.318 0594 0.878 0.396 1.2 1.5 0.486 0.583 D
C. Foundation Recommendations
14. Footings: We recommend that the proposed structures be supported on
conventional, individual-spread and/or continuous footing foundations bearing
on undisturbed formational materials or on properly compacted fill soils over
formational soils. No footings should be underlain by undocumented fill soils.
All building footings should be built on formational soils or properly compacted
fill prepared as recommended above in Recommendation Nos. 3, 4 and 5. The
footings should be founded at least 18 inches below the lowest adjacent
finished grade when founded into properly compacted fill or formational soils.
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Footings located adjacent to utility trenches should have their bearing surfaces
situated below an imaginary 1.0:1.0 plane projected upward from the bottom
edge of the adjacent utility trench. Otherwise, the utility trenches should be
excavated farther from the footing locations.
Footings located adjacent to the tops of slopes should be extended sufficiently
deep so as to provide at least 8 feet of horizontal cover between the slope face
and outside edge of the footing at the footing bearing level.
15. Bearing Values: At the recommended depths, footings on formational or
properly compacted fill soils may be designed for allowable bearing pressures
of 2,500 psf for combined dead and live loads and 3,325 psf for all loads,
including wind or seismic. The footings should, however, have a minimum
width of 15 inches. An increase in soil allowable static bearing can be used as
follows: 800 psf for each additional foot over 1.5 feet in depth and 400 psf for
each additional foot in width to a total not exceeding 4,000 psf. The static soil
bearing value may be increased one-third for seismic and wind load analysis.
As previously indicated, all of the foundations for the building should be built
on dense formational soils or properly compacted fill soils.
16. Footing Reinforcement: All continuous footings should contain top and bottom
reinforcement to provide structural continuity and to permit spanning of local
irregularities. We recommend that a minimum of two No. 5 top and two No.
5 bottom reinforcing bars be provided in the footings. All footings should be
reinforced as specified by the structural engineer. A minimum clearance of 3
inches should be maintained between steel reinforcement and the bottom or
sides of the footing. Isolated square footings should contain, as a minimum,
a grid of three No. 4 steel bars on 12-inch centers, both ways. In order for us
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to offer an opinion as to whether the footings are founded on soils of sufficient
load bearing capacity, it is essential that our representative inspect the footing
excavations prior to the placement of reinforcing steel or forms.
NOTE: The project Civil/Structural Engineer should review all reinforcing
schedules. The reinforcing minimums recommended herein are not to be
construed as structural designs, but merely as minimum reinforcement to
reduce the potential for cracking and separations.
17. Lateral Loads: Lateral load resistance for the structure supported on footing
foundations may be developed in friction between the foundation bottoms and
the supporting subgrade. An allowable friction coefficient of 0.35 is considered
applicable. An additional allowable passive resistance equal to an equivalent
fluid weight of 275 pounds per cubic foot (pcf) acting against the foundations
may be used in design provided the footings are poured neat against the dense
formational or properly compacted fill materials. These lateral resistance value
assume a level surface in front of the footing for a minimum distance of three
times the embedment depth of the footing and any shear keys, but not less
than 8 feet from a slope face, measured from effective top of foundation.
Retaining walls supporting surcharge loads or affected by upper foundations
should consider the effect of those upper loads.
18. Settlement: Settlements under structural design loads are expected to be
within tolerable limits for the proposed structures. For footings designed in
accordance with the recommendations presented in the preceding paragraphs,
we anticipate that the total and differential static settlement for the proposed
improvements will be on the order of 1-inch and approximately, post-
construction differential settlement angular rotation should be less than 1/240.
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D. Concrete Slab On-Grade Criteria
Slabs on-grade may only be used on new, properly compacted fill or when bearing
on dense formational soils.
19. Minimum Floor Slab Thickness and Reinforcement: Based on our experience,
we have found that, for various reasons, floor slabs occasionally crack.
Therefore, we recommend that all slabs on-grade contain at least a minimum
amount of reinforcing steel to reduce the separation of cracks, should they
occur. Slab subgrade soil should be verified by a Geotechnical Exploration,
Inc. representative to have the proper moisture content within 48 hours prior
to placement of the vapor barrier and pouring of concrete.
New interior floor slabs should be a minimum of 4-inches actual thickness and
be reinforced with No. 4 bars on 18-inch centers, both ways, placed at mid-
height in the slab. Soil moisture content should be kept above the optimum
prior to waterproofing placement under the new concrete slab. Shrinkage
joints shall be specified by the structural engineer.
We note that shrinkage cracking can result in reflective cracking in brittle
flooring surfaces such as stone and tiles. It is imperative that if movement
intolerant flooring materials are to be utilized, the flooring contractor and/or
architect should provide specifications for the use of high-quality isolation
membrane products installed between slab and floor materials.
20. Slab Moisture Emission: Although it is not the responsibility of geotechnical
engineering firms to provide moisture protection recommendations, as a
service to our clients we provide the following discussion and suggested
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minimum protection criteria. Actual recommendations should be provided by
the project architect and waterproofing consultants or product manufacturer.
It is recommended to contact the vapor barrier manufacturer to schedule a
pre-construction meeting and to coordinate a review, in-person or digital, of
the vapor barrier installation.
Soil moisture vapor can result in damage to moisture-sensitive floors, some
floor sealers, or sensitive equipment in direct contact with the floor, in addition
to mold and staining on slabs, walls and carpets. The common practice in
Southern California is to place vapor retarders made of PVC, or of polyethylene.
PVC retarders are made in thickness ranging from 10- to 60-mil. Polyethylene
retarders, called visqueen, range from 5- to 10-mil in thickness. These
products are no longer considered adequate for moisture protection and can
actually deteriorate over time.
Specialty vapor retarding and barrier products possess higher tensile strength
and are more specifically designed for and intended to retard moisture
transmission into and through concrete slabs. The use of such products is
highly recommended for reduction of floor slab moisture emission.
The following American Society for Testing and Materials (ASTM) and American
Concrete Institute (ACI) sections address the issue of moisture transmission
into and through concrete slabs: ASTM E1745-17 Standard Specification for
Plastic Water Vapor Retarders Used in Contact Concrete Slabs; ASTM E1643-
18a Standard Practice for Selection, Design, Installation, and Inspection of
Water Vapor Retarders Used in Contact with Earth or Granular Fill Under
Concrete Slabs; ACI 302.2R-06 Guide for Concrete Slabs that Receive
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Moisture-Sensitive Flooring Materials; and ACI 302.1R-15 Guide to Concrete
Floor and Slab Construction.
20.1 Based on the above, we recommend that the vapor barrier consist of a
minimum 15-mil extruded polyolefin plastic (no recycled content or
woven materials permitted). Permeance as tested before and after
mandatory conditioning (ASTM E1745 Section 7.1 and subparagraphs
7.1.1-7.1.5) should be less than 0.01 perms (grains/square
foot/hour/per inch of Mercury) and comply with the ASTM E1745-17
Class A requirements. Installation of vapor barriers should be in
accordance with ASTM E1643-18a. The basis of design is 15-mil Stego
Wrap vapor barrier placed per the manufacturer’s guidelines. Reef
Industries Vapor Guard membrane has also been shown to achieve a
permeance of less than 0.01 perms. We recommend that the slab be
poured directly on the vapor barrier, which is placed directly on the
prepared properly compacted smooth subgrade soil surface.
20.2 Common to all acceptable products, vapor retarder/barrier joints must
be lapped at least 6 inches. Seam joints and permanent utility
penetrations should be sealed with the manufacturer’s recommended
tape or mastic. Edges of the vapor retarder should be extended to
terminate at a location in accordance with ASTM E1643-18a or to an
alternate location that is acceptable to the project’s structural engineer.
All terminated edges of the vapor retarder should be sealed to the
building foundation (grade beam, wall, or slab) using the manufacturer’s
recommended accessory for sealing the vapor retarder to pre-existing
or freshly placed concrete. Additionally, in actual practice, stakes are
often driven through the retarder material, equipment is dragged or
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rolled across the retarder, overlapping or jointing is not properly
implemented, etc. All these construction deficiencies reduce the
retarder’s effectiveness. In no case should retarder/barrier products be
punctured or gaps be allowed to form prior to or during concrete
placement. Vapor barrier-safe screeding and forming systems should
be used that will not leave puncture holes in the vapor barrier, such as
Beast Foot (by Stego Industries) or equivalent.
20.3 Vapor retarders/barriers do not provide full waterproofing for structures
constructed below free water surfaces. They are intended to help reduce
or prevent vapor transmission and/or capillary migration through the
soil and through the concrete slabs. Waterproofing systems must be
designed and properly constructed if full waterproofing is desired. The
owner and project designers should be consulted to determine the
specific level of protection required.
20.4 Following placement of any concrete floor slabs, sufficient drying time
must be allowed prior to placement of floor coverings. Premature
placement of floor coverings may result in degradation of adhesive
materials and loosening of the finish floor materials.
21. Exterior Slab Thickness and Reinforcement: As a minimum for protection of
on-site improvements, we recommend that all exterior pedestrian concrete
slabs be 4 inches thick and be founded on properly compacted and tested fill,
with No. 3 bars at 15-inch centers, both ways, at the center of the slab, and
contain adequate isolation and control joints. The performance of on-site
improvements can be greatly affected by soil base preparation and the quality
of construction. It is therefore important that all improvements are properly
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designed and constructed for the existing soil conditions. The improvements
should not be built on loose soils or fills placed without our observation and
testing.
For exterior slabs with the minimum shrinkage reinforcement, control joints
should be placed at spaces no farther than 15 feet apart or the width of the
slab, whichever is less, and also at re-entrant corners. Control joints in
exterior slabs should be sealed with elastomeric joint sealant. The sealant
should be inspected every 6 months and be properly maintained
E. Retaining Wall Design Criteria
22. Design Parameters – Unrestrained: The active earth pressure to be utilized in
the design of any cantilever site retaining walls, utilizing on-site low- expansive
[EI less than 50] or imported very low- to low-expansive soils [EI less than
50] as backfill should be based on an Equivalent Fluid Weight of 38 pcf (for
level backfill only). For 2.0:1.0 sloping backfill, the cantilever site retaining
walls should be designed with an equivalent fluid pressure of 52 pcf.
Unrestrained retaining walls should be backfilled with properly compacted very
low to low expansive soils. Unrestrained building retaining walls should be
designed for 38 pcf for level low expansive soil backfill, and use a conversion
load factor of 0.31 for vertical surcharge loads to be converted to uniform
lateral surcharge loads. Temporary cantilever shoring walls may use 45 pcf
active pressure, and a conversion factor of 0.36 to convert vertical uniform
surcharge to horizontal uniform pressure. For passive resistance, use the
value of 685 pcf times the diameter of the soldier pile, times the depth of
embedment below the grade excavation in front of the piles.
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23. Design Parameters – Restrained: Temporary or permanent site restrained
shoring walls or restrained building retaining walls supporting low expansive
level backfill may utilize a triangular pressure increasing at a rate of 56 pcf for
wall design (78 pcf for sloping 2.0:1.0 backfill). The soil pressure produced by
any footings, improvements, or any other surcharge placed within a horizontal
distance equal to the height of the retaining portion of the wall should be
included in the wall design pressure. A conversion factor of 0.47 pcf may be
used to convert vertical uniform surcharge loads to lateral uniform pressure
behind a restrained retaining wall with level backfill and 0.64 when supporting
a 2 to 1 sloping backfill. The recommended lateral soil pressures are based on
the assumption that no loose soils or unstable soil wedges will be retained by
the retaining wall. Backfill soils should consist of low-expansive soils with EI
less than 50, and should be placed from the heel of the foundation to the
ground surface within the wedge formed by a plane at 30 from vertical, and
passing by the heel of the foundation and the back face of the retaining wall.
24. Retaining Wall Seismic Design Pressures: For seismic design of unrestrained
walls over 6 feet in exposed height, we recommend that the seismic pressure
increment be taken as a fluid pressure distribution utilizing an equivalent fluid
weight of 16 pcf. This seismic increment is waived for restrained basement
walls. If the walls are designed as unrestrained walls, then the seismic load
should be added to the static soil pressure.
25. Basement/Retaining Wall Drainage: The preceding design pressures assume
that the walls are backfilled with properly compacted low expansion potential
materials (Expansion Index less than 50) and that there is sufficient drainage
behind the walls to prevent the build-up of hydrostatic pressures from surface
water infiltration. We recommend that drainage be provided by a composite
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drainage material such as J-Drain 200/220 and J-Drain SWD, or equivalent.
No perforated pipes or gravel are utilized with the J-Drain system. The drain
material should terminate 12 inches below the exterior finish surface where
the surface is covered by slabs or 18 inches below the finish surface in
landscape areas (see Figure No. VI for Schematic Retaining Wall Subdrain
Recommendations). Waterproofing should extend from the bottom to the top
of the wall.
Backfill placed behind retaining walls should be compacted to a minimum
degree of compaction of 90 percent using light compaction equipment. If
heavy equipment is used, the walls should be appropriately temporarily
braced. Crushed rock gravel may only be used as backfill in areas where
access is too narrow to place compacted soils. Behind shoring walls sand slurry
backfill may be used behind lagging.
Geotechnical Exploration, Inc. will assume no liability for damage to
structures or improvements that is attributable to poor drainage. The
architectural plans should clearly indicate that subdrains for any lower-level
walls be placed at an elevation at least 1 foot below the bottom of the lower-
level slabs.
F. Slopes
26. Temporary Slopes: Based on our subsurface investigation work, laboratory
test results, and engineering analysis, temporary cut slopes up to 12 feet in
height in the formational materials should be stable from mass instability at
an inclination 0.75 :1.0 (horizontal to vertical). Temporary cut slopes up to
12 feet in height in loose fill soils should be stable against mass instability at
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an inclination of 1.5:1.0. In properly compacted fill soils, temporary slopes
should be stable at a slope ratio of 1.0 to 1.0.
Some localized sloughing or raveling of the soils exposed on the slopes may
occur. Since the stability of temporary construction slopes will depend largely
on the contractor's activities and safety precautions (storage and equipment
loadings near the tops of cut slopes, surface drainage provisions, etc.), it
should be the contractor's responsibility to establish and maintain all
temporary construction slopes at a safe inclination appropriate to the methods
of operation. No soil stockpiles or surcharge may be placed within a horizontal
distance of 10 feet or the depth of the excavation, whichever is larger, from
the excavation top.
If these recommendations are not feasible due to space constraints, temporary
shoring may be required for safety and to protect adjacent property
improvements. Similarly, footings near temporary cuts should be underpinned
or protected with shoring.
27. Slope Observations: A representative of Geotechnical Exploration, Inc.
must observe any steep temporary slopes during construction. In the event
that soils and formational material comprising a slope are not as anticipated,
any required slope design changes would be presented at that time.
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28. Permanent Slopes: Any new or existing cut or fill slopes up to 10 feet in height
should be constructed at an inclination of 2.0:1.0 (horizontal to vertical), be
provided with a keyway at least 2 feet in depth and at least 8 feet in width for
the entire length of the slope. Permanent slopes at a 2.0:1.0 slope ratio should
possess a factor of safety of 1.5 against deep and shallow failure.
G. Pavements
29. Concrete Pavement: We recommend that driveways subject only to
automobile and light truck traffic be 5.5 inches thick and be supported directly
on properly prepared/compacted on-site subgrade soils. The upper 6 inches
of the subgrade below the slab should be compacted to a minimum degree of
compaction of 95 percent just prior to paving. The concrete should conform
to Section 201 of The Standard Specifications for Public Works Construction,
2015 Edition, for Class 560-C-3250.
In order to control shrinkage cracking, we recommend that saw-cut,
weakened-plane joints be provided at about 12-foot centers both ways and at
reentrant corners. The pavement slabs should be saw-cut as soon as practical
but no more than 24 hours after the placement of the concrete. The depth of
the joint should be one-quarter of the slab thickness and its width should not
exceed 0.02-foot. Reinforcing steel is not necessary unless it is desired to
increase the joint spacing recommended above.
30. Interlocking Permeable Pavers: If desired, we recommend that permeable
pavement pavers for the driveway, subject only to automobile and light truck
traffic, be supported on a 1.5 inches of bedding sand No. 8 Sand, on 6-inch
thickness of Crushed Miscellaneous Base conforming to Section 200-2 of the
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Standard Specifications for Public Works Construction, 2018 Edition; or 6
inches of No.57 crushed rock gravel per ASTM D448 gradation. The upper 6
inches of the pavement subgrade soil as well as the aggregate base layer
should be compacted to a minimum degree of compaction of 95 percent.
Preparation of the subgrade and placement of the base materials should be
performed under the observation of our representative.
H. Site Drainage Considerations
31. Erosion Control: Appropriate erosion control measures should be taken at all
times during and after construction to prevent surface runoff waters from
entering footing excavations or ponding on finished building pad areas.
32. Surface Drainage: Adequate measures should be taken to properly finish-
grade the lot after the structures and other improvements are in place.
Drainage waters from this site and adjacent properties should be directed away
from the footings, floor slabs, and slopes, onto the natural drainage direction
for this area or into properly designed and approved drainage facilities
provided by the project civil engineer. Roof gutters and downspouts should be
installed on the residence, with the runoff directed away from the foundations
via closed drainage lines. Proper subsurface and surface drainage will help
minimize the potential for waters to seek the level of the bearing soils under
the footings and floor slabs.
Failure to observe this recommendation could result in undermining and
possible differential settlement of the structure or other improvements on the
site or cause other moisture-related problems. Currently, the CBC requires a
minimum 1-percent surface gradient for proper drainage of building pads
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unless waived by the building official. Concrete pavement may have a
minimum gradient of 0.5-percent.
33. Planter Drainage: Planter areas, flower beds and planter boxes should be
sloped to drain away from the footings and floor slabs at a gradient of at least
5 percent within 5 feet from the perimeter walls. Any planter areas adjacent
to the residence or surrounded by concrete improvements should be provided
with sufficient area drains to help with rapid runoff disposal. No water should
be allowed to pond adjacent to the residence or other improvements or
anywhere on the site.
34. Drainage Quality Control: It must be understood that it is not within the scope
of our services to provide quality control oversight for surface or subsurface
drainage construction or retaining wall sealing and base of wall drain
construction. It is the responsibility of the contractor to verify proper wall
sealing, geofabric installation, protection board (if needed), drain depth below
interior floor or yard surface, pipe percent slope to the outlet, etc.
I. General Recommendations
35. Project Start Up Notification: In order to reduce work delays during site
development, this firm should be contacted 48 hours prior to any need for
observation of footing excavations or field density testing of compacted fill
soils. If possible, placement of formwork and steel reinforcement in footing
excavations should not occur prior to observing the excavations; in the event
that our observations reveal the need for deepening or re-designing foundation
structures at any locations, any formwork or steel reinforcement in the affected
footing excavation areas would have to be removed prior to correction of the
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observed problem (i.e., deepening the footing excavation, recompacting soil
in the bottom of the excavation, etc.).
36. Cal-OSHA: Where not superseded by specific recommendations presented in
this report, trenches, excavations, and temporary slopes at the subject site
should be constructed in accordance with Title 8, Construction Safety Orders,
issued by Cal-OSHA.
37. Construction Best Management Practices (BMPs): Construction BMPs must be
implemented in accordance with the requirements of the controlling
jurisdiction. Sufficient BMPs must be installed to prevent silt, mud or other
construction debris from being tracked into the adjacent street(s) or storm
water conveyance systems due to construction vehicles or any other
construction activity. The contractor is responsible for cleaning any such
debris that may be in the street at the end of each work day or after a storm
event that causes breach in the installed construction BMPs.
All stockpiles of uncompacted soil and/or building materials that are intended
to be left unprotected for a period greater than 7 days are to be provided with
erosion and sediment controls. Such soil must be protected each day when
the probability of rain is 40% or greater. A concrete washout should be
provided on all projects that propose the construction of any concrete
improvements that are to be poured in place. All erosion/sediment control
devices should be maintained in working order at all times. All slopes that are
created or disturbed by construction activity must be protected against erosion
and sediment transport at all times. The storage of all construction materials
and equipment must be protected against any potential release of pollutants
into the environment.
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XI. GRADING NOTES
Geotechnical Exploration, Inc. recommends that we be retained to verify the
actual soil conditions revealed during site grading work and footing excavation to be
as anticipated in this "Report of Preliminary Geotechnical Investigation" for the
project. In addition, the placement and compaction of any fill or backfill soils during
site grading work must be observed and tested by the soil engineer.
It is the responsibility of the grading contractor and general contractor to comply with
the requirements on the grading plans as well as the local grading ordinance. All
retaining wall and trench backfill should be properly compacted. Geotechnical
Exploration, Inc. will assume no liability for damage occurring due to improperly or
uncompacted backfill placed without our observations and testing.
XII. LIMITATIONS
Our conclusions and recommendations have been based on available data obtained
from our field investigation and laboratory analysis, as well as our experience with
similar soils and formational materials located in this area of Carlsbad. Of necessity,
we must assume a certain degree of continuity between exploratory excavations
and/or natural exposures. It is, therefore, necessary that all observations,
conclusions, and recommendations be verified at the time grading operations begin
or when footing excavations are placed. In the event discrepancies are noted,
additional recommendations may be issued, if required.
The work performed and recommendations presented herein are the result of an
investigation and analysis that meet the contemporary standard of care in our
profession within the County of San Diego. No warranty is provided.
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As stated previously, it is not within the scope of our services to provide quality
control oversight for surface or subsurface drainage construction or retaining wall
sealing and base of wall drain construction. It is the responsibility of the contractor
to verify proper wall sealing, geofabric installation, protection board installation (if
needed), drain depth below interior floor or yard surfaces; pipe percent slope to the
outlet, etc.
This report should be considered valid for a period of two (2) years, and is subject to
review by our firm following that time. If significant modifications are made to the
building plans, especially with respect to the height and location of any proposed
structures, this report must be presented to us for immediate review and possible
revision.
It is the responsibility of the owner and/or developer to ensure that the
recommendations summarized in this report are carried out in the field operations
and that our recommendations for design of this project are incorporated in the
project plans. We should be retained to review the project plans once they are
available, to verify that our recommendations are adequately incorporated in the
plans. Additional or modified recommendations may be issued if warranted after plan
review.
This firm does not practice or consult in the field of safety engineering. We do not
direct the contractor's operations, and we cannot be responsible for the safety of
personnel other than our own on the site; the safety of others is the responsibility of
the contractor. The contractor should notify the owner if any of the recommended
actions presented herein are considered to be unsafe.
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The firm of Geotechnical Exploration, Inc. shall not be held responsible for
changes to the physical condition of the property, such as addition of fill soils or
changing drainage patterns, which occur subsequent to issuance of this report and
the changes are made without our observations, testing, and approval.
Once again, should any questions arise concerning this report, please feel free to
contact the undersigned. Reference to our Job No. 20-12942 will expedite a reply
to your inquiries.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________ ______________________________
Jaime A. Cerros, P.E. Hector G. Estrella, C.E.G.
R.C.E. 34422/G.E. 2007 Engineering Geologist
Senior Geotechnical Engineer P.G. 9019/C.E.G. 2656
REFERENCES
JOB NO. 20-12942
November 2020
2007 Working Group on California Earthquake Probabilities, 2008, The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2), U.S Geological Survey Open-file Report 2007-1437 and
California Geological Survey Special Report 203.
Association of Engineering Geologists, 1973, Geology and Earthquake Hazards, Planners Guide to the
Seismic Safety Element, Association of Engineering Geologists, Southern California Section.
Berger, V. and Schug, D.L., 1991, Probabilistic Evaluation of Seismic Hazard in the San Diego-Tijuana
Metropolitan Region, Environmental Perils, San Diego Region, Geological Society of America by the San
Diego Association of Geologists, October 20, 1991, p. 89-99.
Crowell, J.C., 1962, Displacement Along the San Andreas, Fault, California, Geological Society of
America, Special Papers, no. 71.
Demere, T.A. 1997, Geology of San Diego County, California, San Diego Natural History Museum,
http://archive.sdnhm.org/research/paleontology/sdgeol.html, accessed July 30, 2020.
Grant Ludwig, L.B. and Shearer, P.M., 2004, Activity of the Offshore Newport-Inglewood Rose Canyon
Fault Zone, Coastal Southern California, from Relocated Microseismicity. Bulletin of the Seismological
Society of America, 94(2), 747-752.
Greene, H.G., Bailey, K.A., Clarke, S.H., Ziony, J.I. and Kennedy, M.P., 1979, Implications of fault
patterns of the inner California continental borderland between San Pedro and San Diego, in Abbott,
P.L., and Elliot, W.J., eds., Earthquakes and other perils, San Diego region: San Diego Association of
Geologists, Geological Society of America field trip, November, 1979, p. 21–28.
Greensfelder, R.W., 1974, Maximum Credible Rock Accelerations from Earthquakes in California,
California Division of Mines and Geology.
Hart E.W. and Bryant, W.A., 1997, Fault-Rupture Hazard Zones in California, California Division of Mines
and Geology, Special Publication 42.
Hart, E.W., Smith, D.P. and Saul, R.B., 1979, Summary Report: Fault Evaluation Program, 1978 Area (Peninsular Ranges-Salton Trough Region), California Division of Mines and Geology, Open-file Report
79-10 SF, 10.
Hauksson, E. and Jones, L.M., 1988, The July 1986 Oceanside (ML=5.3) Earthquake Sequence in the
Continental Borderland, Southern California Bulletin of the Seismological Society of America, v. 78, p.
1885-1906.
Hileman, J.A., Allen, C.R. and Nordquist, J.M., 1973, Seismicity of the Southern California Region,
January 1, 1932 to December 31, 1972; Seismological Laboratory, Cal-Tech, Pasadena, California.
Kennedy, M.P. and Tan, S.S., 2007, Geologic Map of the Oceanside 30’x60’ Quadrangle, California,
California Geological Survey, Department of Conservation.
Richter, C.F., 1958, Elementary Seismology, W.H. Freeman and Company, San Francisco, California.
REFERENCES/Page 2
Rockwell, T.K., 2010, The Rose Canyon Fault Zone in San Diego, Proceedings of the Fifth International
Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. Paper No.
7.06C.
Rockwell, T.K., Dawson, T.E., Young Ben-Horin, J. and Seitz, G., 2014, A 21-Event, 4,000-Year History
of Surface Ruptures in the Anza Seismic Gap, San Jacinto Fault, and Implications for Long-term
Earthquake Production on a Major Plate Boundary Fault. Pure and Applied Geophysics, v. 172, 1143–
1165 (2015).
Rockwell, T.K., Millman, D.E., McElwain, R.S. and Lamar, D.L., 1985, Study of Seismic Activity by
Trenching Along the Glen Ivy North Fault, Elsinore Fault Zone, Southern California: Lamar-Merifield
Technical Report 85-1, U.S.G.S. Contract 14-08-0001-21376, 19 p.
Ross, Z.E., Hauksson E. and Ben-Zion Y., 2017, Abundant Off-fault Seismicity and Orthogonal Structures in the San Jacinto Fault Zone, Science Advances, 2017; 3(3): e1601946. Published 2017 Mar 15.
Toppozada, T.R. and Parke, D.L., 1982, Areas Damaged by California Earthquakes, 1900-1949,
California Division of Mines and Geology, Open-file Report. 82-17.
U.S. Dept. of Agriculture, 1953, Aerial Photographs AXN-14M-19 and 20.
VICINITY MAP
Garfield Street Condominiums
4008 Garfield Street
Carlsbad, CA.Figure No. I
Job No. 20-12942
SITE
Thomas Guide San Diego County Edition pg 1106-E7
Existing StrutureApproximate Locationof Exploratory HandpitHP-5HP-2HP-1HP-4HP-3HP-5Job No. 20-12942REFERENCE: This PLOT PLAN was prepared from an existing TOPOGRAPHIC SURVEY MAP by PASCO LARET SUITEER &ASSOCIATES dated 08/03/20 and from on-site field reconnaissance performed by GEI.Scale: 1” =20’(approximate)LEGENDNOTE: This Plot Plan is not to be used for legal purposes. Locations and dimensions are approximate. Actual property dimensions and locations of utilities may be obtained from the Approved Building Plans or the “As-Built” Grading Plans.20-12942-p.aiPLOT PLAN ANDSITE SPECIFICGEOLOGIC MAPGAR
FI
E
L
D
S
T
R
E
E
T November 2020CHINQUAPIN AVENUEOld Paralic Deposits( units 6-7 ) QopGEOLOGIC LEGENDQop6-7QafQop6-7QafQop6-7QafQop6-7QafQop6-7QafQafArtificial Fill6-7Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.Figure No. IIa
Proposed StrutureApproximate Locationof Exploratory HandpitHP-5HP-2HP-1HP-4HP-3HP-5Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.Figure No. IIbJob No. 20-12942REFERENCE: This PLOT PLAN was prepared from an existing undated PRELIMINARY PAD EXHIBIT by PASCO LARET SUITER & ASSOCIATES and from on-site field reconnaissance performed by GEI.Scale: 1” =20’(approximate)LEGENDNOTE: This Plot Plan is not to be used for legal purposes. Locations and dimensions are approximate. Actual property dimensions and locations of utilities may be obtained from the Approved Building Plans or the “As-Built” Grading Plans.20-12942-p2.aiPLOT PLAN ANDSITE SPECIFICGEOLOGIC MAPGAR
FI
E
L
D
S
T
R
E
E
T November 2020CHINQUAPIN AVENUEOld Paralic Deposits( units 6-7 ) QopGEOLOGIC LEGENDQop6-7QafQop6-7QafQop6-7QafQop6-7QafQop6-7QafQafArtificial Fill6-7
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/WEATHERED OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Dense to very dense.
Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 1.5'
106.9
SM
SM
SM
1.2DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
JOB NUMBERSAMPLE
HP-1
DATE LOGGED
± 67' Mean Sea Level
IIIa
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 1.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes medium dense to dense.
-- 16% passing #200 sieve.
SILTY SANDSTONE. Dense to very dense.
Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes mottled, red-brown and light brown.
Bottom @ 4.5'
106.9
102.4
105.7
120.76.4
SM
SM
SM
2.3
2.5
2.2DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
5
JOB NUMBERSAMPLE
HP-2
DATE LOGGED
± 67' Mean Sea Level
IIIb
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 4.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Dense to very dense.Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 3.5'
105.6
SM
SM
SM
1.8DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
JOB NUMBERSAMPLE
HP-3
DATE LOGGED
± 64' Mean Sea Level
IIIc
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 3.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)-- becomes medium dense to dense.
SILTY SANDSTONE. Medium dense to dense.
Damp. Light tan.
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes very dense.
-- 16% passing #200 sieve.
Bottom @ 5'
102.6
SM
SM
SM
2.4DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
5
6
JOB NUMBERSAMPLE
HP-4
DATE LOGGED
± 61.5' Mean Sea Level
IIId
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
2
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Medium dense to dense.
Damp. Light tan.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 3.5'
SM
SM
SMDEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
JOB NUMBERSAMPLE
HP-5
DATE LOGGED
± 59' Mean Sea Level
IIIe
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 3.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
75
80
85
90
95
100
105
110
115
120
125
130
135
0 5 10 15 20 25 30 35 40 45
WATER CONTENT, %
MOISTURE-DENSITY RELATIONSHIP
TEST RESULTS
Maximum Dry Density
Optimum Water Content 6.4
Source of Material
Description of Material
DRY DENSITY, pcfSILTY SAND (SM), Brown
ASTM D1557 Method A
HP-2 @ 2.5'
120.7 PCF
%
Curves of 100% Saturationfor Specific Gravity Equal to:
2.80
2.70
2.60
Test Method
Expansion Index (EI)
Figure Number: IV
Job Name: Garfield Street Residential Project
Site Location: 4008 Garfield Street, Carlsbad, CA
Job Number: 20-12942COMPACTION + EI DARK GRID 12942 GARFIELD-RINCON.GPJ GEI FEB06.GDT 11/16/20
L A B O R A T O R Y R E P O R T
Telephone (619) 425-1993 Fax 425-7917 Established 1928
C L A R K S O N L A B O R A T O R Y A N D S U P P L Y I N C.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Sales Order Number: 50003
Account Number: GEOE.R5
To:
*-------------------------------------------------*
Geotechnical Exploration Inc.
7420 Trade Street
San Diego, Ca 92121
Attention: Hector Estrella
Laboratory Number: SO8034-1 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation:
*-------------------------------------------------*
One soil sample received on 11/30/20 at 12:30pm,
from Garfield marked as HP-2@2-4.
Division of Construction, Method for Estimating the Service Life of
Steel Culverts.
pH 7.2
Water Added (ml) Resistivity (ohm-cm)
10 12000
5 9500
5 7700
5 7000
5 5800
5 6000
5 6200
41 years to perforation for a 16 gauge metal culvert.
53 years to perforation for a 14 gauge metal culvert.
73 years to perforation for a 12 gauge metal culvert.
94 years to perforation for a 10 gauge metal culvert.
114 years to perforation for a 8 gauge metal culvert.
Water Soluble Sulfate Calif. Test 417 <0.003%
Water Soluble Chloride Calif. Test 422 0.003%
_______________
Rosa Bernal
RMB/dbb
Analysis By California Test 643, 1999, Department of Transportation
Date: December 9, 2020
Purchase Order Number: GARFIELD
L A B O R A T O R Y R E P O R T
Telephone (619) 425-1993 Fax 425-7917 Established 1928
C L A R K S O N L A B O R A T O R Y A N D S U P P L Y I N C.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Date: December 9, 2020
Purchase Order Number: GARFIELD
Sales Order Number: 50003
Account Number: GEOE.R5
To:
*-------------------------------------------------*
Geotechnical Exploration Inc.
7420 Trade Street
San Diego, Ca 92121
Attention: Hector Estrella
Laboratory Number: SO8034-2 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation:
*-------------------------------------------------*
One soil sample received on 11/30/20 at 12:30pm,
from Garfield marked as HP-4@3-5.
Analysis By California Test 643, 1999, Department of Transportation
Division of Construction, Method for Estimating the Service Life of
Steel Culverts.
pH 6.9
Water Added (ml) Resistivity (ohm-cm)
10 27000
5 17000
5 13000
5 9800
5 8800
5 9100
5 9600
36 years to perforation for a 16 gauge metal culvert.
47 years to perforation for a 14 gauge metal culvert.
65 years to perforation for a 12 gauge metal culvert.
83 years to perforation for a 10 gauge metal culvert.
101 years to perforation for a 8 gauge metal culvert.
Water Soluble Sulfate Calif. Test 417 <0.003%
Water Soluble Chloride Calif. Test 422 0.001%
_______________
Rosa Bernal
RMB/dbb
Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.SITEFigure No. V Job No. 20-12942EXCERPT FROMNovember 2020Garfield-Condos-2008-geo.aiPacificOcean
11/12/2020 U.S. Seismic Design Maps
https://seismicmaps.org 1/3
40087 Garfield
4008 Garfield St, Carlsbad, CA 92008, USA
Latitude, Longitude: 33.1469608, -117.3424812
Date 11/12/2020, 4:09:08 PM
Design Code Reference Document ASCE7-16
Risk Category II
Site Class C - Very Dense Soil and Soft Rock
Type Value Description
SS 1.098 MCER ground motion. (for 0.2 second period)
S1 0.396 MCER ground motion. (for 1.0s period)
SMS 1.318 Site-modified spectral acceleration value
SM1 0.594 Site-modified spectral acceleration value
SDS 0.878 Numeric seismic design value at 0.2 second SA
SD1 0.396 Numeric seismic design value at 1.0 second SA
Type Value Description
SDC D Seismic design category
Fa 1.2 Site amplification factor at 0.2 second
Fv 1.5 Site amplification factor at 1.0 second
PGA 0.486 MCEG peak ground acceleration
FPGA 1.2 Site amplification factor at PGA
PGAM 0.583 Site modified peak ground acceleration
TL 8 Long-period transition period in seconds
SsRT 1.098 Probabilistic risk-targeted ground motion. (0.2 second)
SsUH 1.231 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration
SsD 1.5 Factored deterministic acceleration value. (0.2 second)
S1RT 0.396 Probabilistic risk-targeted ground motion. (1.0 second)
S1UH 0.438 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration.
S1D 0.6 Factored deterministic acceleration value. (1.0 second)
PGAd 0.596 Factored deterministic acceleration value. (Peak Ground Acceleration)
CRS 0.892 Mapped value of the risk coefficient at short periods
18 November 2021
Rincon Real Estate Group Job No. 20-12942
3005 S. El Camino Real
San Clemente, CA 92672
Attn: Mr. Kevin Dunn
Subject: Response to Third-Party Reviewer (First); Project No. 9493.1;
Log No. 21609
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
MS2021-0001
Dear Mr. Dunn:
As requested and required by the City of Carlsbad third-party geotechnical reviewer
(Hetherington Engineering, Inc.) in a letter dated September 14, 2021, we herein
respond to their review comments. The third-party reviewer has reviewed our
“Report of Preliminary Geotechnical Investigation” dated December 9, 2020, as well
as undated Grading Plans for Garfield Homes, 4008 Garfield Street, by Pasco Laret
Suiter and Associates (7 sheets).
REVIEW COMMENTS & RESPONSES
1. The consultant should review the project grading plan (Reference 2) and
foundation plans, provide any additional geotechnical analyses/recommenda-
tions considered necessary, and confirm that the plans have been prepared in
accordance with the geotechnical recommendations.
GEI Response: We have reviewed the project grading plans (Reference 2).
The grading plans are in accordance with the geotechnical recommendations
presented in the referenced geotechnical report. We understand that the
foundation plans have not been completed, and we will review them for
compliance when available.
Rincon Garfield Street Project Job No. 20-12942
Carlsbad, California Page 2
2. The consultant should provide an updated geotechnical map utilizing the
current grading plan for the project to clearly show (at minimum): a) existing
site topography, b) proposed structures/improvements, c) proposed finished
grades, d) geologic conditions, e) locations of the subsurface exploration, f)
temporary construction slopes, g) remedial grading, etc.
GEI Response: We have included an updated geotechnical Plot Plan (see
Appendix A) showing the existing and proposed structures and improvements,
proposed finish grades, locations of subsurface exploration and geologic
contacts on a topographic base map. The temporary excavations are not
shown since they are to be executed in an alternating “A-B-C” slot method. It
is anticipated that the temporary slots will be no taller than 3½ feet for the
new property line retaining walls. The total slot width of the recommended
slots should be no longer than 8 feet. Other interior excavations deeper than
3 feet can be made at 1.0:1.0 slope ratio. Temporary excavations are
anticipated at proposed retaining wall locations shown in the grading plan.
Remedial grading is anticipated for all areas to receive exterior hardscape
improvements, buildings, and retaining walls and should to extend at least 5
feet beyond the perimeter of these areas where feasible.
3. The Consultant stated in the text that seismic Site Class D was assigned to the
site. The attached seismic design parameters were based on a Site Class C.
The consultant should address and revise recommendations as needed.
GEI Response: This was a typographical error in the text of the report. Our
exploratory logs indicate that the formational soils encountered at shallow
depth are dense to very dense and, therefore, seismic Site Class C
classification is applicable.
4. Foundation and slab design criteria for expansive soils should be consistent
with Section 1808.6 of the 2019 California Building Code. The consultant
should provide expansion index test results and update foundation
recommendations, as necessary.
GEI Response: We performed expansion index tests on two soil samples
retrieved from the site. One sample was from the western half of the site and
the other from the eastern half. The tests yielded an expansion index of 2 for
the western half and 3 for the eastern half. Therefore, the soils can be
classified as having a very low expansion potential and no special
recommendations are required for foundations or slabs on-grade due to soil
expansivity. No updated recommendations are needed.
Rincon Garfield Street Project Job No. 20-12942
Carlsbad, California Page 3
5. The consultant should provide a list of recommended testing/observations
during grading and construction.
GEI Response: During grading, our firm should observe the bottom of
excavations, perform field density tests of placed and compacted soils at least
every 2 feet in thickness, verify the adequacy of soil moisture content and
relative compaction, obtain and verify the maximum dry density of the soils
being placed as fill material, and verify the adequacy of imported soils by
performing sieve tests and expansion index tests as well as maximum dry
density and optimum moisture tests.
In addition, we should verify soil moisture content and compaction of on-site
soils being used for trench and retaining wall backfill, verify adequacy and
moisture content of subgrade soils to receive pavement or flatwork
improvements, in public street areas obtain soil samples and perform R-value
tests in areas to receive pavement (if required to verify adequacy of pavement
cross sections), verify adequacy of compaction of asphalt concrete, verify
adequacy of grain size of base material as well as determination of maximum
dry density in the laboratory as well as relative compaction in the field.
If you have any questions regarding this letter, please contact our office. Reference
to our Job No. 20-12942 will help expedite a response to your inquiry.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________ ______________________________
Jaime A. Cerros, P.E. Leslie D. Reed, President
R.C.E. 34422/G.E.2007 C.E.G. 999/P.G. 3391
Senior Geotechnical Engineer
APPENDIX A
Updated Geotechnical Plot Plan
Approximate Locationof Proposed StructureHP-5HP-4HP-3HP-2HP-1HP-5Qop6-7QafQop6-7QafQop6-7QafQop6-7QafQop6-7QafQopQaf6-7Old Paralic Deposits( units 6-7 ) GEOLOGIC LEGENDArtificial FillApproximate Locationof Exploratory Handpit20-12942-P4.aiREFERENCE: This Plot Plan was prepared from an existing undated GRADING PLAN providedPASCO LARET SUITER & ASSOCIATES and from on-site field reconnaissance performed by GEI.NOTE: This Plot Plan is not to be used for legalpurposes. Locations and dimensions are approximate.Actual property dimensions and locations of utilitiesmay be obtained from the Approved Building Plansor the “As-Built” Grading Plans.Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.Figure No. IIJob No. 20-12942Scale: 1” =5’(approximate)PLOT PLAN ANDSITE SPECIFICGEOLOGIC MAPGARFIELD STREETCHINQUAPIN AVENUE(updated November 2021)LEGEND
UPDATED REPORT OF PRELIMINARY GEOTECHNICAL
INVESTIGATION
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
JOB NO. 20-12942
15 December 2021
Prepared for:
Rincon Homes
Job No. 20-12942
15 December 2021
Rincon Homes
5315 Avenida Encinitas, Suite 200
Carlsbad, CA 92008
Attn: Mr. Thomas St. Clair
Subject: Updated Report of Preliminary Geotechnical Investigation
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
Dear Mr. St. Clair:
Per the request of Mr. Bryan Knapp with Pasco Laret Suiter and as required by City
of Carlsbad third-party reviewer (Hetherington Engineering, Inc.), Geotechnical
Exploration, Inc. has updated the geotechnical investigation for the subject project.
The field work was performed on October 26, 2020. The original “Report of
Preliminary Geotechnical Investigation” is dated December 9, 2020.
If the conclusions and recommendations presented in this report are incorporated
into the design and construction of the proposed three-story, single-family residences
with attached garages, detached accessory dwelling units, and associated
improvements, it is our opinion that the site is suitable for the proposed project.
This opportunity to be of service is sincerely appreciated. Should you have any
questions concerning the following report, please do not hesitate to contact us.
Reference to our Job No. 20-12942 will expedite a response to your inquiries.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________
Jaime A. Cerros, P.E.
Senior Geotechnical Engineer
R.C.E. 34422/G.E. 2007
TABLE OF CONTENTS
I. PROJECT SUMMARY ............................................................................. 1
II. SCOPE OF WORK ................................................................................. 2
III. SITE DESCRIPTION .............................................................................. 2
IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING .............................. 3
V. LABORATORY TESTING & SOIL INFORMATION ......................................... 4
VI. REGIONAL GEOLOGIC DESCRIPTION ...................................................... 8
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION ................................... 13
VIII. GEOLOGIC HAZARDS ......................................................................... 15
A. Local and Regional Faults ............................................................ 15
B. Other Geologic Hazards .............................................................. 21
IX. GROUNDWATER ................................................................................ 24
X. CONCLUSIONS & RECOMMENDATIONS ................................................. 26
A. Preparation of Soils for Site Development ...................................... 28
B. Seismic Design Criteria ............................................................... 35
C. Foundation Recommendations ..................................................... 36
D. Concrete Slab On-Grade Criteria .................................................. 38
E. Retaining Wall Design Criteria ...................................................... 43
F. Slopes ...................................................................................... 45
G. Pavements ................................................................................ 47
H. Site Drainage Considerations ....................................................... 48
I. General Recommendations .......................................................... 49
XI. GRADING NOTES ............................................................................... 50
XII. LIMITATIONS .................................................................................... 51
REFERENCES
FIGURES
I. Vicinity Map
II. Updated Plot Plan and Site-Specific Geologic Map
IIIa-e. Exploratory Boring Logs and Laboratory Results
IVa-c. Laboratory Test Results
V. Geologic Map Excerpt and Legend
VI. Schematic Retaining Wall Subdrain Recommendations
APPENDICES
A. Unified Soil Classification System
B. ASCE Seismic Summary Report
UPDATED REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
JOB NO. 20-12942
The following report presents the findings and recommendations of Geotechnical
Exploration, Inc. for the subject project.
I. PROJECT SUMMARY
It is our understanding, based on our review of the available plans prepared by Kirk
Moeller Architects, Inc., and Pasco Laret Suiter and Associates (references), that the
existing two-story, split-level single-family residential structure and the existing one-
story building located to the northeastern portion of the property and associated
improvements are to be entirely demolished and replaced with three, 3-story, multi-
family structures with attached garages, 4- to 6-foot-high retaining walls, and
associated improvements. The new structures are to be constructed of standard-
type building materials utilizing conventional foundations with concrete slab on-
grade. Foundation loads are expected to be typical for this type of relatively light
construction. A preliminary site plan by Kirk Moeller Architects, Inc., dated August
17, 2020, has been reviewed by us and used to understand the scope of the project.
When final plans are completed, they should be made available for our review.
Additional or modified recommendations will be provided at that time if warranted.
This updated report has been prepared to incorporate comments response to the city
third-party reviewer.
Based on the available information at this stage, it is our opinion that the proposed
site development would not destabilize neighboring properties or induce the
settlement of adjacent structures or improvements if designed and constructed in
accordance with our recommendations.
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II. SCOPE OF WORK
The scope of work performed for this investigation included a site reconnaissance and
subsurface exploration program under the direction of our geologist with placement,
logging and sampling of five exploratory trenches, review of available published
information pertaining to the site geology, laboratory testing, geotechnical
engineering analysis of the field and laboratory data, and the preparation of this
report. The data obtained and the analyses performed were for the purpose of
providing design and construction criteria for the project earthwork, building
foundations, retaining walls, slab on-grade floors and associated improvements.
III. SITE DESCRIPTION
The lot is known as Assessor’s Parcel No. 206-080-01-00, with a current address of
4008 Garfield Street in the City of Carlsbad, County of San Diego, State of California.
Refer to Figure No. I, Vicinity Map, for the site location.
The square footage of the rectangular-shaped lot is reported in the referenced plans
as 6,001 square feet (0.14 AC). The property is bordered on the north by Chinquapin
Avenue, on the west by Garfield Street, and on the east and south by two single-
family residential structures. Refer to Figure No. II, Updated Plot Plan and Site-
Specific Geologic Map. The plot plan has been updated to include surveyed
information.
The existing property is currently developed with a two-story, split-level, single-
family residential structure and an existing one-story building located on the
northeastern portion of the property, landscape areas and associated improvements.
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Vegetation on the site primarily consists of an ornamental garden, shrubbery, weeds,
grasses and mature trees.
The property slopes down from the western property line to the eastern property line.
Approximate elevations across the property range from approximately +59 feet
above Mean Sea Level (MSL) along the eastern side of the site to approximately +67
feet above MSL at the western portion of the property. Survey information
concerning elevations across the site was obtained from the topographic survey
template of the preliminary site plan by Pasco Laret Suiter, dated August 03, 2020.
IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING
The field investigation was conducted on October 26, 2020, and consisted of surface
reconnaissance and a subsurface exploration program utilizing hand-excavated
exploratory test trenches to investigate and sample the subsurface soils. Five (5)
exploratory trenches (HP-1 to HP-5) were excavated to a maximum depth of 5 feet
in the areas of the proposed development and associated improvements. The
excavations revealed that the building site is underlain by approximately 6 inches of
loose to medium dense, silty sand fill soil over medium dense, silty sand natural
residual soil, mantling medium dense to dense formational materials. The soils
encountered in the exploratory trenches are considered to have a low expansion
potential with an Expansion Index of less than 50. The exploratory excavations were
continuously logged in the field by our geologist and described in accordance with
the Unified Soil Classification System (refer to Appendix A). The approximate
locations of the exploratory trenches are shown on Figure No. II, Updated Plot Plan
and Site-Specific Geologic Map.
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Representative samples were obtained from the exploratory trenches at selected
depths appropriate to the investigation. Relatively undisturbed chunk and drive
samples and disturbed bulk samples were collected from the exploratory trenches to
aid in classification and for appropriate laboratory testing. The samples were
returned to our laboratory for evaluation and testing. Exploratory trench logs have
been prepared on the basis of our observations and laboratory test results, and are
attached as Figure Nos. IIIa-e.
The exploratory trench logs and related information depict subsurface conditions only
at the specific locations shown on the plot plan and on the particular date designated
on the logs. Subsurface conditions at other locations may differ from conditions
occurring at the locations. Also, the passage of time may result in changes in
subsurface conditions due to environmental changes.
V. LABORATORY TESTING & SOIL INFORMATION
Laboratory tests were performed on retrieved soil samples in order to evaluate their
physical and mechanical properties. The test results are presented on Figure Nos.
IIIa-e and IVa-c. The following tests were conducted on representative soil samples:
1. Moisture Content (ASTM D2216-19)
2. Density Measurements (ASTM D2937-17e2)
3. Standard Test Method for Bulk Specific Gravity and Density of Com-
pacted Bituminous Mixtures using Coated Samples (ASTM D1188-07)
4. Laboratory Compaction Characteristics (ASTM D1557-12e1)
5. Determination of Percentage of Particles Smaller than #200
Sieve (ASTM D1140-17)
6. Resistivity and pH Analysis (Department of Transportation
California Test 643)
7. Water Soluble Sulfate (Dept of Transportation California Test 417)
8. Water Soluble Chloride (Dept of Transportation California Test 422)
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Moisture content and density measurements were performed by ASTM methods
D2216-19 and D2937-17e2 respectively, in conjunction with D1188-07 to establish
the in-situ moisture and density of samples retrieved from the exploratory trenches.
Measurements were also performed by ASTM method D1188-07, the bulk specific
gravity utilizing paraffin-coated specimens. This method helps to establish the in-
situ density of chunk samples retrieved from formational exposures/outcrops. The
test results are presented on the trench logs at the appropriate sample depths and
laboratory test results.
Laboratory compaction values (ASTM D1557-12e1) establish the optimum moisture
content and the laboratory maximum dry density of the tested soils. The relationship
between the moisture and density of remolded soil samples helps to establish the
relative compaction of the existing fill soils and soil compaction conditions to be
anticipated during any future grading operation. The test results are presented on
the trench logs at the appropriate sample depths and laboratory test results.
The particle size smaller than a No. 200 sieve analysis (ASTM D1140-17) aids in
classifying the tested soils in accordance with the Unified Soil Classification System
and provides qualitative information related to engineering characteristics such as
expansion potential, permeability, and shear strength. Our laboratory testing
indicated 16 percent of the sample passing the No. 200 sieve. The test results are
presented on the trench logs at the appropriate sample depths and laboratory test
results.
The expansion potential of soils is determined, when necessary, utilizing the Standard
Test Method for Expansion Index of Soils (ASTM D4829-19). In accordance with the
Standard (Table 5.3), potentially expansive soils are classified as follows:
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EXPANSION INDEX POTENTIAL EXPANSION
0 to 20 Very low
21 to 50 Low
51 to 90 Medium
91 to 130 High
Above 130 Very high
We performed expansion index tests on two soil samples retrieved from the site after
our original geotechnical report was issued, as requested by the third-party reviewer.
One sample was from the western half of the site and the other from the eastern half
of the site. The test results yielded an expansion index of 2 for the western half and
3 for the eastern half. Therefore, the soils can be classified as having a very low
expansion potential. Special recommendations are not required for the foundations
or slabs on-grade due to soil expansivity.
To assess soil corrosivity of the on-site soils, resistivity, pH, chloride and soluble
sulfate tests were performed by an outside consultant (Clarkson Laboratory and
Supply Inc.) on samples of the near surface soils most likely to be in contact with
concrete and ferrous metals. The most common factor in determining soils corrosivity
to ferrous metals is electrical resistivity. As soils’ resistivity decreases, its corrosivity
to ferrous metals increases. The tested soils yielded low resistivities of 8,800 and
5,800 Ohm-cm, indicating that the soils are mildly corrosive to ferrous metals.
Soils and fluids are considered neutral when pH is measured at 7, acidic when pH is
measured at <7 and alkaline when measured at >7. Soils are considered corrosive
when the pH gets down to around 5.5 or less. Results of the laboratory testing
yielded pH values of 7.2 and 6.9, indicating that the tested soils range from slightly
acid to slightly alkaline, indicating that pH is not a significant factor in soil corrosivity
to metals.
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Large concentrations of chlorides will adversely affect any ferrous metals such as iron
and steel. Soil with a chloride concentration greater than or equal to 500 ppm (0.05
percent) or more is considered corrosive to ferrous metals. The chloride content of the
tested soils measured at approximately 30 and 10 ppm or 0.003 and 0.0010 percent
respectively, indicating that chloride is not a major factor in corrosion to ferrous
metals.
The primary cause of deterioration of concrete in foundations and other below ground
structures is the corrosive attack by soluble sulfates present in the soil and
groundwater. The results of water-soluble sulfate testing performed on a
representative sample of the near surface soils in the general area of the proposed
structures, yielded soluble sulfate contents of less than 30 ppm or 0.003 percent,
indicating that the proposed cement-concrete structures that are in contact with the
underlying soils are anticipated to be affected with a negligible sulfate exposure. As
such, there is no restriction on selection of cement type.
The table below summarizes the laboratory results for chemical testing of the
sampled soils:
Sample Location/
Depth (ft) pH Soluble Sulfate
(PPM)
Soluble
Chloride
(PPM)
Soil Resistivity
(Ohm-cm)
HP-2 / 2.0-4.0 7.2 <30 30 5,800
HP-4 / 3.0-5.0 6.9 <30 10 8,800
The laboratory testing results are presented in Figure Nos. IVa-c. It should be noted
that Geotechnical Exploration Inc., does not practice corrosion engineering and
our assessment here should be construed as an aid to the owner or owner’s
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representative. A corrosion specialist should be consulted for any specific design
requirement.
Based on the field and laboratory test data, our observations of the primary soil types,
and our previous experience with laboratory testing of similar soils, our Geotechnical
Engineer has assigned values for friction angle, coefficient of friction, and cohesion
for those soils that will have significant lateral support or load bearing functions on
the project. The assumed soil strength values were utilized in determining the
recommended bearing value as well as active and passive earth pressure design
criteria for foundations and retaining walls. The assumed strength values for properly
compacted fill and for dense formational soils are 33 degrees and cohesion equal to
50 psf, as well as total unit weight of 120 pcf are based on the visual inspection of
the soils and our experience. With these values we calculated the ultimate bearing
capacity of the soil to be 9,285 psf by Terzaghi’s equation. This value was reduced
with a factor of safety of 3 to calculate the allowable bearing capacity of 3,095 psf,
which has been reduced to the nominal recommended value of 2,500 psf. The active
and passive pressure of the soils were calculated with Terzaghi’s equations for those
pressures and neglecting the cohesion contribution to values of 35.4 pcf and 407 pcf.
We have increased the active soil pressure to 38 pcf, and the passive soil pressure
was reduced to 275 pcf. The calculated friction coefficient of 0.649 has been reduced
to an allowable value of 0.35.
VI. REGIONAL GEOLOGIC DESCRIPTION
San Diego County has been divided into three major geomorphic provinces: The
Coastal Plain, the Peninsular Ranges and the Salton Trough. The Coastal Plain exists
west of the Peninsular Ranges. The Salton Trough is east of the Peninsular Ranges.
These divisions are the result of the basic geologic distinctions between the areas.
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Mesozoic metavolcanic, metasedimentary and plutonic rocks predominate in the
Peninsular Ranges with primarily Cenozoic sedimentary rocks to the west and east of
this central mountain range (Demere, 1997).
In the Coastal Plain region, where the subject property is located, the “basement”
consists of Mesozoic crystalline rocks. Basement rocks are also exposed as high relief
areas (e.g., Black Mountain northeast of the subject property and Cowles Mountain
near the San Carlos area of San Diego). Younger Cretaceous and Tertiary sediments
lap up against these older features. These sediments form a “layer cake” sequence
of marine and non-marine sedimentary rock units, with some formations up to 140
million years old. Faulting related to the La Nación and Rose Canyon Fault zones has
broken up this sequence into a number of distinct fault blocks in the southwestern
part of the county. Northwestern portions of the county are relatively undeformed
by faulting (Demere, 1997).
The Peninsular Range form the granitic spine of San Diego County. These rocks are
primarily plutonic, forming at depth beneath the earth’s crust 140 to 90 million years
ago as the result of the subduction of an oceanic crustal plate beneath the North
American continent. These rocks formed the much larger Southern California
batholith. Metamorphism associated with the intrusion of these great granitic masses
affected the much older sediments that existed near the surface over that period of
time. These metasedimentary rocks remain as roof pendants of marble, schist, slate,
quartzite and gneiss throughout the Peninsular Ranges. Locally, Miocene-age
volcanic rocks and flows have also accumulated within these mountains (e.g.,
Jacumba Valley). Regional tectonic forces and erosion over time have uplifted and
unroofed these granitic rocks to expose them at the surface (Demere, 1997).
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The Salton Trough is the northerly extension of the Gulf of California. This zone is
undergoing active deformation related to faulting along the Elsinore and San Jacinto
Fault Zones, which are part of the major regional tectonic feature in the southwestern
portion of California, the San Andreas Fault Zone. Translational movement along
these fault zones has resulted in crustal rifting and subsidence. The Salton Trough,
also referred to as the Colorado Desert, has been filled with sediments to depth of
approximately 5 miles since the movement began in the early Miocene, 24 million
years ago. The source of these sediments has been the local mountains as well as
the ancestral and modern Colorado River (Demere, 1997).
As indicated previously, the San Diego area is part of a seismically active region of
California. It is on the eastern boundary of the Southern California Continental
Borderland, part of the Peninsular Ranges Geomorphic Province. This region is part
of a broad tectonic boundary between the North American and Pacific Plates. The
actual plate boundary is characterized by a complex system of active, major, right-
lateral strike-slip faults, trending northwest/southeast. This fault system extends
eastward to the San Andreas Fault (approximately 70 miles from San Diego) and
westward to the San Clemente Fault (approximately 50 miles off-shore from San
Diego) (Berger and Schug, 1991).
In California, major earthquakes can generally be correlated with movement on
active faults. As defined by the California Division of Mines and Geology, now the
California Geological Survey, an "active" fault is one that has had ground surface
displacement within Holocene time, about the last 11,000 years (Hart and Bryant,
1997). Additionally, faults along which major historical earthquakes have occurred
(about the last 210 years in California) are also considered to be active (Association
of Engineering Geologist, 1973). The California Division of Mines and Geology defines
a "potentially active" fault as one that has had ground surface displacement during
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Quaternary time, that is, between 11,000 and 1.6 million years (Hart and Bryant,
1997).
During recent history, prior to April 2010, the San Diego County area has been
relatively quiet seismically. No fault ruptures or major earthquakes had been
experienced in historic time within the greater San Diego area. Since earthquakes
have been recorded by instruments (since the 1930s), the San Diego area has
experienced scattered seismic events with Richter magnitudes generally less than
M4.0. During June 1985, a series of small earthquakes occurred beneath San Diego
Bay, three of which were recorded at M4.0 to M4.2. In addition, the Oceanside
earthquake of July 13, 1986, located approximately 26 miles offshore of the City of
Oceanside, had a magnitude of M5.3 (Hauksson and Jones, 1988).
On June 15, 2004, a M5.3 earthquake occurred approximately 45 miles southwest of
downtown San Diego (26 miles west of Rosarito, Mexico). Although this earthquake
was widely felt, no significant damage was reported. Another widely felt earthquake
on a distant southern California fault was a M5.4 event that took place on July 29,
2008, west-southwest of the Chino Hills area of Riverside County.
Several earthquakes ranging from M5.0 to M6.0 occurred in northern Baja California,
centered in the Gulf of California on August 3, 2009. These were felt in San Diego
but no injuries or damage was reported. A M5.8 earthquake followed by a M4.9
aftershock occurred on December 30, 2009, centered about 20 miles south of the
Mexican border city of Mexicali. These were also felt in San Diego, swaying high-rise
buildings, but again no significant damage or injuries were reported.
On April 4, 2010, a large earthquake occurred in Baja California, Mexico. It was
widely felt throughout the southwest including Phoenix, Arizona and San Diego in
California. This M7.2 event, the Sierra El Mayor earthquake, occurred in northern
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Baja California, approximately 40 miles south of the Mexico-USA border at shallow
depth along the principal plate boundary between the North American and Pacific
plates. According to the U. S. Geological Survey this is an area with a high level of
historical seismicity, and it has recently also been seismically active, although this is
the largest event to strike in this area since 1892. The April 4, 2010, earthquake
appears to have been larger than the M6.9 earthquake in 1940 or any of the early
20th century events (e.g., 1915 and 1934) in this region of northern Baja California.
The event caused widespread damage to structures, closure of businesses,
government offices and schools, power outages, displacement of people from their
homes and injuries in the nearby major metropolitan areas of Mexicali in Mexico and
Calexico in Southern California.
This event's aftershock zone extends significantly to the northwest, overlapping with
the portion of the fault system that is thought to have ruptured in 1892. Some
structures in the San Diego area experienced minor damage and there were some
injuries. Ground motions for the April 4, 2010, main event, recorded at stations in
San Diego and reported by the California Strong Motion Instrumentation Program
(CSMIP), ranged up to 0.058g.
On July 7, 2010, a M5.4 earthquake occurred in Southern California at 4:53 pm
(Pacific Time) about 30 miles south of Palm Springs, 25 miles southwest of Indio, and
13 miles north-northwest of Borrego Springs. The earthquake occurred near the
Coyote Creek segment of the San Jacinto Fault. The earthquake exhibited right
lateral slip to the northwest, consistent with the direction of movement on the San
Jacinto Fault. The earthquake was felt throughout Southern California, with strong
shaking near the epicenter. It was followed by more than 60 aftershocks of M1.3
and greater during the first hour.
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In the last 50 years, there have been four other earthquakes in the magnitude M5.0
range within 20 kilometers of the Coyote Creek segment: M5.8 in 1968, M5.3 on
2/25/1980, M5.0 on 10/31/2001, and M5.2 on 6/12/2005. The biggest earthquake
near this location was the M6.0 Buck Ridge earthquake on 3/25/1937.
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION
Our field investigation, reconnaissance and review of the geologic map by Kennedy
and Tan, 2007, “Geologic Map of the Oceanside 30’x60’ Quadrangle, California”
indicate that the site is underlain at depth by late to middle Pleistocene-Aged Old
Paralic Deposits, Units 6-7 (Qop6-7) formational materials. An excerpt of the
geological map is included as Figure No. V. Our exploratory trenches indicate the
formational materials are overlain across the site by artificial fill soils (Qaf) and
subsoil/residual soil. Site-specific geology is mapped on Figure No. II, the Updated
Plot Plan and Site-Specific Geologic Map.
Fill Soil (Qaf): Our site investigation indicates that the areas in the general vicinity
of our exploratory trenches at the site are overlain by up to 12 inches of fill soil. The
encountered fill soil consists of fine- to medium-grained, dry to moist, gray-brown to
red-brown to brown, silty sands (SM) with variable amounts of roots. The fill soils
are generally loose. In our opinion, due to the variable density and poor condition of
the fill soil, it is not considered suitable in its current condition to support loads from
structures or additional fill. Refer to Figure Nos. IIIa-e for details.
Residual Soil/Subsoil: Residual soil/subsoil was encountered underlying the fill soils
in all the exploratory trenches. The approximate thickness of these soils was
observed to vary from approximately 6 inches to 3 feet in thickness. These soils
were noted to consist mainly of damp, light-brown, silty sands (SM). This material
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was observed to be generally loose to medium dense, porous and with some deeper
roots. In our opinion, due to the low density and potential compressibility of these
porous soils, these residual soils are not considered suitable to support loads from
structures or additional fill in their current condition. Refer to Figure Nos. IIIa-e for
details.
Old Paralic Deposits, Unit 6-7 (Qop6-7): The encountered formational materials are
described in the literature as Quaternary (late to middle Pleistocene Old Paralic
Deposits, Units 6-7. These formational materials were encountered in all trenches
underlying the residual soil at variable depths from 1 to 2.5 feet. The formational
materials consist of fine- to medium-grained, damp to moist, red-brown silty sands
(SM) with areas of moderate cementation and some deeper roots. The formational
materials underlying the site are dense to very dense. In our opinion, the dense to
very dense nature of the Old Paralic Deposits, Units 6-7, makes it suitable in its
current condition to support loads from structures or additional fill. Refer to Figure
Nos. IIIa-e for details.
Based on our review of the “Geologic Map of the Oceanside 30’x60’ Quadrangle,
California” by Kennedy and Tan, 2007, the Old Paralic Deposits, Units 6-7,
formational materials underlie the entire site at depth. The aforementioned Old
Paralic Deposit Units are described as “Poorly sorted, moderately permeable, reddish-
brown, interfingered strandline, beach, estuarine and colluvial deposits composed of
siltstone, sandstone and conglomerate.” According to the map, there are no faults
known to pass through the site (refer to Figure No. V, Geologic Map Excerpt and
Legend).
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VIII. GEOLOGIC HAZARDS
The following is a discussion of the geologic conditions and hazards common to this
area of Carlsbad, as well as project-specific geologic information relating to
development of the subject site.
A. Local and Regional Faults
Reference to the Geologic Map and Legend, Figure No. V (Kennedy and Tan, 2007),
indicates that no faults are shown to cross the site. Furthermore, our site
reconnaissance presented no indications of faulting crossing the site. In our
professional opinion, neither an active fault nor a potentially active fault underlies
the site.
A brief description of the nearby active faults including distances from the mapped
fault to the subject site at the closest point (based on the USGS Earthquake Hazards-
Interactive Fault Map), is presented below:
Newport-Inglewood-Rose Canyon Fault Zone System: The Oceanside section of the
Newport-Inglewood-Rose Canyon Fault Zone is mapped approximately 4.3 miles
west-southwest of the site. The offshore portion of the Newport-Inglewood Fault
Zone is described as a right-lateral, local reverse slip associated with fault steps
(SCEDC, 2020). The reported length is 46.2 miles extending in a northwest-
southeast direction. Surface trace is discontinuous in the Los Angeles Basin, but the
fault zone can easily be noted there by the existence of a chain of low hills extending
from Culver City to Signal Hill. South of Signal Hill, it roughly parallels the coastline
until just south of Newport Bay, where it heads offshore, and becomes the Newport-
Inglewood - Rose Canyon Fault Zone. A significant earthquake (M6.4) occurred along
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this fault on March 10, 1933. Since then, no additional significant events have
occurred. The fault is believed to have a slip rate of approximately 0.6-mm/yr with
an unknown recurrence interval. This fault is believed capable of producing an
earthquake of M6.0 to M7.4 (Grant Ludwig and Shearer, 2004).
Rose Canyon Fault Zone: The Rose Canyon Fault Zone is the southern section of the
Newport-Inglewood-Rose Canyon Fault Zone system mapped in the San Diego
County area as trending north-northwest to south-southeast from Oceanside to La
Jolla and generally north-south into San Diego Bay, through Coronado and offshore
downtown San Diego, from where it appears to head southward. The Rose Canyon
Fault Zone system is considered to be a complex zone of onshore and offshore, en
echelon right lateral, strike slip, oblique reverse, and oblique normal faults. This fault
is considered to be capable of generating an M7.2 earthquake and is considered
microseismically active, although no significant recent earthquakes since 1769 are
known to have occurred on the fault.
Investigative work on faults that are part of the Rose Canyon Fault Zone at the Police
Administration and Technical Center in downtown San Diego, at the SDG&E facility in
Rose Canyon, and within San Diego Bay and elsewhere within downtown San Diego,
has encountered offsets in Holocene (geologically recent) sediments. These findings
confirm Holocene displacement on the Rose Canyon Fault, which was designated an
“active” fault in November 1991 (Hart and Bryant, 1997).
Rockwell (2010) has suggested that the Rose CFZ underwent a cluster of activity
including 5 major earthquakes in the early Holocene, with a long period of inactivity
following, suggesting major earthquakes on the RCFZ behaves in a cluster-mode,
where earthquake recurrence is clustered in time rather than in a consistent
recurrence interval. With the most recent earthquake (MRE) nearly 500 years ago,
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it is suggested that a period of earthquake activity on the RCFZ may have begun.
Rockwell (2010) and a compilation of the latest research implies a long-term slip rate
of approximately 1 to 2 mm/year.
Coronado Bank Fault: The Coronado Bank Fault is located approximately 22.6 miles
southwest of the site. Evidence for this fault is based upon geophysical data (acoustic
profiles) and the general alignment of epicenters of recorded seismic activity (Greene
et al., 1979). The Oceanside earthquake of M5.3 recorded July 13, 1986, is known
to have been centered on the fault or within the Coronado Bank Fault Zone. Although
this fault is considered active, due to the seismicity within the fault zone, it is
significantly less active seismically than the Elsinore Fault (Hileman et al., 1973). It
is postulated that the Coronado Bank Fault is capable of generating a M7.6
earthquake and is of great interest due to its close proximity to the greater San Diego
metropolitan area.
San Diego Trough Fault Zone: The San Diego Trough Fault Zone is mapped
approximately 29.6 miles west-southwest of the site at its closest point. This fault is
described as a right-lateral type fault with a length of at least 93.2 miles and a slip
rate of roughly 1.5 mm/yr. The most recent surface rupture is of Holocene age
(SCEDC, 2020).
San Clemente Fault Zone: The San Clemente Fault Zone is mapped at approximately
56 miles southwest of the site at its closest point. This fault is described as a right-
lateral and vertical offsets type fault with a length of at least 130.5 miles described
as essentially continuous with the San Isidro fault zone, off the coast of Mexico and
a slip rate of roughly 1.5 mm/yr. The most recent surface rupture is of Holocene age
(SCEDC, 2020).
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Elsinore Fault: The Temecula and Julian sections of the Elsinore Fault Zone are
located approximately 23.5 and 33 miles northeast and east of the site, respectively.
The Elsinore Fault Zone extends approximately 125 miles from the Mexican border
to the northern end of the Santa Ana Mountains. The Elsinore Fault zone is a 1- to
4-mile-wide, northwest-southeast-trending zone of discontinuous and en echelon
faults extending through portions of Orange, Riverside, San Diego, and Imperial
Counties. Individual faults within the Elsinore Fault Zone range from less than 1 mile
to 16 miles in length. The trend, length and geomorphic expression of the Elsinore
Fault Zone identify it as being a part of the highly active San Andreas Fault system.
Like the other faults in the San Andreas system, the Elsinore Fault is a transverse
fault showing predominantly right-lateral movement. According to Hart et al. (1979),
this movement averages less than 1 centimeter per year. Along most of its length,
the Elsinore Fault Zone is marked by a bold topographic expression consisting of
linearly aligned ridges, swales and hallows. Faulted Holocene alluvial deposits
(believed to be less than 11,000 years old) found along several segments of the fault
zone suggest that at least part of the zone is currently active.
Although the Elsinore Fault Zone belongs to the San Andreas set of active, northwest-
trending, right-slip faults in the southern California area (Crowell, 1962), it has not
been the site of a major earthquake in historic time, other than a M6.0 earthquake
near the town of Elsinore in 1910 (Richter, 1958; Toppozada and Parke, 1982).
However, based on length and evidence of late-Pleistocene or Holocene displacement,
Greensfelder (1974) has estimated that the Elsinore Fault Zone is reasonably capable
of generating an earthquake with a magnitude as large as M7.5. Study and logging
of exposures in trenches placed in Glen Ivy Marsh across the Glen Ivy North Fault (a
strand of the Elsinore Fault Zone between Corona and Lake Elsinore), suggest a
maximum earthquake recurrence interval of 300 years, and when combined with
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previous estimates of the long-term horizontal slip rate of 0.8 to 7.0 mm/year,
suggest typical earthquake magnitudes of M6.0 to M7.0 (Rockwell et al., 1985). The
Working Group on California Earthquake Probabilities (2008) has estimated that there
is a 11 percent probability that an earthquake of M6.7 or greater will occur within 30
years on this fault.
San Jacinto Fault: The San Jacinto Fault is located approximately 46 to 66 miles
northeast of the site. The San Jacinto Fault Zone consists of a series of closely spaced
faults, including the Coyote Creek Fault, that form the western margin of the San
Jacinto Mountains. The fault zone extends from its junction with the San Andreas
Fault in San Bernardino, southeasterly toward the Brawley area, where it continues
south of the international border as the Imperial Transform Fault (Rockwell et al.,
2014).
The San Jacinto Fault zone has a high level of historical seismic activity, with at least
10 damaging earthquakes (M6.0 to M7.0) having occurred on this fault zone between
1890 and 1986. Earthquakes on the San Jacinto Fault in 1899 and 1918 caused
fatalities in the Riverside County area. Offset across this fault is predominantly right-
lateral, similar to the San Andreas Fault, although some investigators have suggested
that dip-slip motion contributes up to 10% of the net slip (Ross et al., 2017).
The segments of the San Jacinto Fault that are of most concern to major metropolitan
areas are the San Bernardino, San Jacinto Valley and Anza segments. Fault slip rates
on the various segments of the San Jacinto are less well constrained than for the San
Andreas Fault, but the available data suggest slip rates of 12 ±6 mm/yr for the
northern segments of the fault, and slip rates of 4 ±2 mm/yr for the southern
segments. For large ground-rupturing earthquakes on the San Jacinto fault, various
investigators have suggested a recurrence interval of 150 to 300 years. The Working
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Group on California Earthquake Probabilities (2008) has estimated that there is a 31
percent probability that an earthquake of M6.7 or greater will occur within 30 years
on this fault. Maximum credible earthquakes of M6.7, M6.9 and M7.2 are expected
on the San Bernardino, San Jacinto Valley and Anza segments, respectively, capable
of generating peak horizontal ground accelerations of 0.48g to 0.53g in the County
of Riverside. A M5.4 earthquake occurred on the San Jacinto Fault on July 7, 2010.
The United States Geological Survey has issued the following statements with respect
to the recent seismic activity on southern California faults:
The San Jacinto fault, along with the Elsinore, San Andreas, and other
faults, is part of the plate boundary that accommodates about 2
inches/year of motion as the Pacific plate moves northwest relative to
the North American plate. The largest recent earthquake on the San
Jacinto fault, near this location, the M6.5 1968 Borrego Mountain
earthquake April 8, 1968, occurred about 25 miles southeast of the July
7, 2010, M5.4 earthquake. This M5.4 earthquake follows the 4th of April
2010, Easter Sunday, M7.2 earthquake, located about 125 miles to the
south, well south of the US Mexico international border. A M4.9
earthquake occurred in the same area on June 12th at 8:08 pm (Pacific
Time). Thus, this section of the San Jacinto fault remains active.
Seismologists are watching two major earthquake faults in southern
California. The San Jacinto fault, the most active earthquake fault in
southern California, extends for more than 100 miles from the
international border into San Bernardino and Riverside, a major
metropolitan area often called the Inland Empire. The Elsinore fault is
more than 110 miles long, and extends into the Orange County and Los
Angeles area as the Whittier fault. The Elsinore fault is capable of a
major earthquake that would significantly affect the large metropolitan
areas of southern California. The Elsinore fault has not hosted a major
earthquake in more than 100 years. The occurrence of these
earthquakes along the San Jacinto fault and continued aftershocks
demonstrates that the earthquake activity in the region remains at an
elevated level. The San Jacinto fault is known as the most active
earthquake fault in southern California. Caltech and USGS seismologist
continue to monitor the ongoing earthquake activity using the
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Caltech/USGS Southern California Seismic Network and a GPS network
of more than 100 stations.
B. Other Geologic Hazards
Ground Rupture: Ground rupture is characterized by bedrock slippage along an
established fault and may result in displacement of the ground surface. For ground
rupture to occur along a fault, an earthquake usually exceeds M5.0. If a M5.0
earthquake were to take place on a local fault, an estimated surface-rupture length
1 mile long could be expected (Greensfelder, 1974). Our investigation indicates that
the subject site is not directly on a known active fault trace and, therefore, the risk
of ground rupture is remote.
Ground Shaking: Structural damage caused by seismically induced ground shaking
is a detrimental effect directly related to faulting and earthquake activity. Ground
shaking is considered to be the greatest seismic hazard in San Diego County. The
intensity of ground shaking is dependent on the magnitude of the earthquake, the
distance from the earthquake, and the seismic response characteristics of underlying
soils and geologic units. Earthquakes of M5.0 or greater are generally associated
with significant damage. It is our opinion that the most serious damage to the site
would be caused by a large earthquake originating on a nearby strand of the Rose
Canyon, Coronado Bank or Newport-Inglewood Faults. Although the chance of such
an event is remote, it could occur within the useful life of the structure.
Landslides: Our investigation indicates that the subject site is not directly on a known
recent or ancient landslide. Review of the “Geologic Map of the Oceanside 30’x60’
Quadrangle, California” by Kennedy and Tan (2007) and the USGS Landslide Hazard
Program Site (US Landslide Inventory), indicate that there are no known or suspected
ancient landslides located on the site.
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Slope Stability: Our site reconnaissance indicates that the site slopes gently in an
eastern direction, with only an 8-foot difference in elevation across the area of the
site. The site is underlain by relatively stable and dense Old Paralic Deposits, Unit 6-
7 formational materials at a depth of 1.0 to 3.0 feet. In our opinion, there is not a
slope stability issue with the site.
Liquefaction: The liquefaction of saturated sands during earthquakes can be a major
cause of damage to buildings. Liquefaction is the process by which soils are
transformed into a viscous fluid that will flow as a liquid when unconfined. It occurs
primarily in loose, cohesionless saturated silt, sand, and fine-grained gravel deposits
of Holocene to late Pleistocene age and in areas where the groundwater is shallower
than about 50 feet (DMG Special Publication 117) when they are sufficiently shaken
by an earthquake. On this site, the risk of liquefaction of formational materials due
to seismic shaking is considered to be very low due to the dense to very dense nature
of the underlying formational materials and the lack of shallow static groundwater.
The site does not have a potential for soil strength loss to occur due to a seismic
event.
Tsunamis and Seiches: A tsunami is a series of long waves generated in the ocean
by a sudden displacement of a large volume of water. Underwater earthquakes,
landslides, volcanic eruptions, meteor impacts, or onshore slope failures can cause
this displacement. Tsunami waves can travel at speeds averaging 450 to 600 miles
per hour. As a tsunami nears the coastline, its speed diminishes, its wave length
decreases, and its height increases greatly. After a major earthquake or other
tsunami-inducing activity occurs, a tsunami could reach the shore within a few
minutes. One coastal community may experience no damaging waves while another
may experience very destructive waves. Some low-lying areas could experience
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severe inland inundation of water and deposition of debris more than 3,000 feet
inland.
The site is located approximately 0.17-mile from the exposed coastline and at an
elevation of approximately 59 to 67 feet above MSL. Review of the Tsunami
Inundation Map for Emergency Planning, Encinitas Quadrangle, the site is located
outside the inundation area. There is no risk of tsunami inundation at the site.
A seiche is a run-up of water within a lake or embayment triggered by fault- or
landslide-induced ground displacement. The site is located near a coastal lagoon,
that is not considered capable of producing a seiche and inundating the subject site.
Flood Hazard: Review of the FEMA flood maps number 06073C0764H, effective on
12/20/2019, the project site is located within the Special Flood Hazard Area (SFHA)
X. Zone X is described as minimal flood hazard. The civil engineer should verify this
statement with the City of Carlsbad and County of San Diego (FEMA, 2019).
Geologic Hazards Summary: It is our opinion, based upon a review of the available
maps, our research and our site investigation, that the site is underlain at shallow
depth by stable Old Paralic Deposits formational materials and is suited for the
proposed residential structures. retaining walls and associated improvements
provided the recommendations herein are implemented. Furthermore, based on the
available information at this stage, it appears the proposed site development will not
destabilize or result in settlement of adjacent property or improvements if the
recommendations presented in this report are implemented.
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No significant geologic hazards are known to exist on the site that would prohibit the
construction of the proposed residential structures, retaining walls and associated
improvements. Ground shaking from earthquakes on active southern California faults
and active faults in northwestern Mexico is the greatest geologic hazard at the
property. Design of building structures in accordance with the current building codes
would reduce the potential for injury or loss of human life. Buildings constructed in
accordance with current building codes may suffer significant damage but should not
undergo total collapse.
In our explicit professional opinion, no active or potentially active faults underlie the
project site.
IX. GROUNDWATER
Free groundwater was not encountered in our exploratory excavations to the
maximum depths explored. A more detailed description of the subsurface materials
encountered in our exploratory excavations Figure Nos. IIIa-e.
It should also be recognized that minor groundwater seepage problems might occur
after development of a site even where none were present before development.
These are usually minor phenomena and are often the result of an alteration in
drainage patterns and/or an increase in irrigation water. Based on the permeability
characteristics of the soil and the anticipated usage and development, it is our opinion
that any seepage problems, which may occur, will be minor in extent. It is further
our opinion that these problems can be most effectively corrected on an individual
basis if and when they occur.
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We do not anticipate significant groundwater problems to develop in the future, if the
property is developed as proposed and proper drainage is implemented and
maintained.
It should be kept in mind that any required construction operations will change
surface drainage patterns and/or reduce permeabilities due to the densification of
compacted soils. Such changes of surface and subsurface hydrologic conditions, plus
irrigation of landscaping or significant increases in rainfall, may result in the
appearance of surface or near-surface water at locations where none existed
previously. The damage from such water is expected to be localized and cosmetic in
nature, if good positive drainage is implemented, as recommended in this report,
during and at the completion of construction.
On properties such as the subject site where dense, low permeability soils exist at
shallow depths, even normal landscape irrigation practices on the property or
neighboring properties, or periods of extended rainfall, can result in shallow
“perched” water conditions. The perching (shallow depth) accumulation of water on
a low permeability surface can result in areas of persistent wetting and drowning of
lawns, plants and trees. Resolution of such conditions, should they occur, may
require site-specific design and construction of subdrain and shallow “wick” drain
dewatering systems.
Subsurface drainage with a properly designed and constructed subdrain system will
be required along with continuous back drainage behind any proposed lower-level
basement walls, property line retaining walls, or any perimeter stem walls for raised-
wood floors where the outside grades are higher than the crawl space grades.
Furthermore, crawl spaces, if used, should be provided with the proper cross-
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ventilation to help reduce the potential for moisture-related problems. Additional
recommendations may be required at the time of construction.
It must be understood that unless discovered during site exploration or encountered
during site construction operations, it is extremely difficult to predict if or where
perched or true groundwater conditions may appear in the future. When site fill or
formational soils are fine-grained and of low permeability, water problems may not
become apparent for extended periods of time.
Water conditions, where suspected or encountered during construction, should be
evaluated and remedied by the project civil and geotechnical consultants. The project
developer and property owner, however, must realize that post-construction
appearances of groundwater may have to be dealt with on a site-specific basis.
Proper functional surface drainage should be implemented and maintained at the
property.
X. CONCLUSIONS & RECOMMENDATIONS
The following recommendations are based upon the practical field investigations
conducted by our firm, and resulting laboratory tests, in conjunction with our
knowledge and experience with similar soils in the Carlsbad area. The opinions,
conclusions, and recommendations presented in this report are contingent upon
Geotechnical Exploration, Inc. being retained to review the final plans and
specifications as they are developed and to observe the site earthwork and
installation of foundations. Accordingly, we recommend that the following paragraph
be included on the grading and foundation plans for the project.
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If the geotechnical consultant of record is changed for the project, the
work shall be stopped until the replacement has agreed in writing to
accept responsibility within their area of technical competence for
approval upon completion of the work. It shall be the responsibility of
the permittee to notify the governing agency in writing of such change
prior to the recommencement of grading and/or foundation installation
work and comply with the governing agency’s requirements for a change
to the Geotechnical Consultant of Record for the project.
We recommend that the planned residential structures, garages and retaining walls
be supported by conventional, individual-spread and/or continuous footing
foundations founded on medium dense to dense formational soils and minimum 90
percent compacted structural fill soils. Individual structures may bear on dense
formational or fill soils depending on their locations, final grading elevations and
exposure of formational materials.
Existing fill soils across the entire site will be disturbed during the demolition of the
existing structures, and are not suitable in their current condition to support new
structures or associated improvements. A full removal and recompaction of existing
fill and residual soils across the site will be required to support the proposed
structures and associated improvements. Fill soils across the site will be required to
be compacted to at least 90 percent relative compaction. Existing fill soil and
formational materials are suitable for use as recompacted fill soils. Any buried trash
and roots encountered during site demolition and fill soil recompaction should be
removed and exported off site.
It is our opinion that the site is suitable for the planned residential project provided
the recommendations herein are incorporated during design and construction.
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A. Preparation of Soils for Site Development
1. General: Grading should conform to the guidelines presented in the 2019
California Building Code (CBC), as well as the requirements of the City of
Carlsbad.
During earthwork construction, removals and reprocessing of fill materials, as
well as general grading procedures of the contractor should be observed and
the fill placed selectively tested by representatives of the geotechnical
engineer, Geotechnical Exploration Inc. If any unusual or unexpected
conditions are exposed in the field, they should be reviewed by the
geotechnical engineer and if warranted, modified and/or additional remedial
recommendations will be offered. Specific guidelines and comments pertinent
to the planned development are provided herein.
The recommendations presented herein have been completed using the
information provided to us regarding site development. If information
concerning the proposed development is revised, or any changes in the design
and location of the proposed property modified or approved in writing by this
office.
2. Clearing and Stripping: Complete demolition of the existing residential
structure and associated improvements should be undertaken. This is to
include the complete removal of all subsurface footings, utility lines and
miscellaneous debris. After clearing the entire ground surface of the site
should be stripped of existing vegetation within the areas of proposed new
construction. This includes any roots from existing trees and shrubbery. Holes
resulting from the removal of root systems or other buried obstructions that
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extend below the planned grades should be cleared and backfilled with suitable
compacted material compacted to the requirements provided under
Recommendation Nos. 3, 4 and 5 below. Prior to any filling operations, the
cleared and stripped vegetation and debris should be disposed of off-site.
3. Excavation: After the entire site has been cleared and stripped, all of the
existing fill soils and topsoil should be removed and recompacted. The depth
of removal across the site will vary depending on the thickness of unsuitable
soils overlying the formational materials. It is anticipated that the depth of
removal will be at least 3 feet below existing grade in the area of the existing
house pad, however, shallower removal (at least 2 feet) may be anticipated
across the remainder of the site. Based on the results of our exploratory
trenches and test holes, as well as our experience with similar materials in the
project area, it is our opinion that the existing fill soils and topsoil materials
can be excavated utilizing ordinary light to heavy weight earthmoving
equipment. Contractors should not, however, be relieved of making their own
independent evaluation of excavating the on-site materials prior to submitting
their bids. Contractors should also review this report along with the trench
logs to understand the scope and quantity of grading required for this project.
Variability in excavating the subsurface materials should be expected across
the project area.
The areal extent required to remove the surficial soils should be confirmed by
our representatives during the excavation work based on their examination of
the soils being exposed. The lateral extent of the excavation and recompaction
should be at least 5 feet beyond the edge of the perimeter ground level
foundations of the new residential structure and any areas to receive exterior
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improvements, or fill slopes, where feasible, or to the depth of excavation or
fill at that location, whichever is greater.
4. Cut-Fill Transition: Based on the review of the preliminary survey plans it
appears that the new residential structure may be planned to be constructed
on a cut-fill transition line.
New structures should not bear on a cut-fill transition line. If a cut-fill
transition line exists within the proposed building envelope, we recommend
that the cut portion of the building pad, be undercut to a minimum of 24 inches
below the bottom of the proposed footing depth. The bottom of the over
excavation should be observed and approved by a representative of
Geotechnical Exploration Inc., to verify that all loose and unsuitable soils
have been completely removed prior to reprocessing. After approval, the
bottom of the excavation should be scarified to a minimum depth of 8 inches
below removal grade elevations, brought to near-optimum moisture conditions
and recompacted to at least 90 percent relative compaction (based on ASTM
Test Method D1557). Backfill and compaction of the remaining structural fill
should be performed based on the recommendations presented in the following
sections. No structures should be supported on a building pad with structural
fill soil thickness differential of greater than 5 feet.
5. Subgrade Preparation: After the site has been cleared, stripped, and the
required excavations made, the exposed subgrade soils in areas to receive new
fill and/or slab on-grade building improvements should be scarified to a depth
of 6 inches, moisture conditioned, and compacted to the requirements for
structural fill. While not anticipated, in the event that planned cuts expose any
medium to highly expansive formational materials in the building areas, they
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should be scarified and moisture conditioned to at least 3 percent over
optimum moisture for low expansive soils and 5 percent for medium and highly
expansive soils (if encountered).
6. Material for Fill: Existing on-site low-expansion potential (Expansion Index of
50 or less per ASTM D4829-19) soils with an organic content of less than 3
percent by volume are, in general, suitable for use as fill. Imported fill
material, where required, should have a low-expansion potential. In addition,
both imported and existing on-site materials for use as fill should not contain
rocks or lumps more than 6 inches in greatest dimension if the fill soils are
compacted with heavy compaction equipment (or 3 inches in greatest
dimension if compacted with lightweight equipment). All materials for use as
fill should be approved by our representative prior to importing to the site.
If encountered at the site, medium to highly expansive soils should not be used
as structural fill at a depth of less than 5 feet from footing bearing surface
elevation or behind retaining walls. Backfill material placed behind retaining
walls should be low expansive (E.I. less than 50), with rocks no larger than 3
inches in diameter.
7. Structural Fill Compaction: All structural fill, and areas to receive any
associated improvements, should be compacted to a minimum degree of
compaction of 90 percent based upon ASTM D1557-12e1. Fill material should
be spread and compacted in uniform horizontal lifts not exceeding 8 inches in
uncompacted thickness. Before compaction begins, the fill should be brought
to a water content that will permit proper compaction by either: (1) aerating
and drying the fill if it is too wet, or (2) watering the fill if it is too dry. Each
lift should be thoroughly mixed before compaction to ensure a uniform
distribution of moisture. For low expansive soils, the moisture content should
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be within 2 percent of optimum. Although we do not anticipate any medium
to high expansive soils to be exposed during grading operations, if
encountered, the compaction moisture content should be at least 5 percent
over optimum.
Any rigid improvements founded on the existing undocumented fill soils can
be expected to undergo movement and possible damage. Geotechnical
Exploration, Inc. takes no responsibility for the performance of any
improvements built on loose natural soils or inadequately compacted fills.
Subgrade soils in any exterior area receiving concrete improvements should
be verified for compaction and moisture by a representative of our firm within
48 hours prior to concrete placement.
No uncontrolled fill soils should remain after completion of the site work. In
the event that temporary ramps or pads are constructed of uncontrolled fill
soils, the loose fill soils should be removed and/or recompacted prior to
completion of the grading operation. Based on the results of our laboratory
testing, the water-soluble sulfate content of the tested soils at the site yielded
a negligible sulfate exposure, as such based on table 1904.3 of the building
code, there is no restrictions for cement type.
8. Trench and Retaining Wall Backfill: All utility trenches and retaining walls
should be backfilled with properly compacted fill. Backfill material should be
placed in lift thicknesses appropriate to the type of compaction equipment
utilized and compacted to a minimum degree of compaction of 90 percent
based upon ASTM D1557-12e1 by mechanical means. Any portion of the
trench backfill in public street areas within pavement sections should conform
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to the material and compaction requirements of the adjacent pavement
section.
Backfill soils placed behind retaining walls should be installed as early as the
retaining walls are capable of supporting lateral loads. Backfill soils behind
retaining walls should be low expansive (Expansion Index less than 50 per
ASTM D4829-19).
Our experience has shown that even shallow, narrow trenches (such as for
irrigation and electrical lines) that are not properly compacted can result in
problems, particularly with respect to shallow groundwater accumulation and
migration.
9. Observations and Testing: During grading, our firm should observe and test
the grading soils as stated in CBC 2019, Section 1705.6 Soils: “Special
inspections and tests of existing site soil conditions, fill placement and load-
bearing requirements shall be performed in accordance with this section and
Table 1705.6 (see below). The approved geotechnical report and the
construction documents prepared by the registered design professionals shall
be used to determine compliance. During fill placement, the special inspector
shall verify that proper materials and procedures are used in accordance with
the provisions of the approved geotechnical report”.
A summary of Table 1705.6 “REQUIRED SPECIAL INSPECTIONS AND TESTS
OF SOILS” is presented below:
a) Verify materials below shallow foundations are adequate to achieve the
design bearing capacity;
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b)Verify excavations are extended to proper depth and have reached
proper material;
c)Perform classification and testing of compacted fill materials;
d)Verify use of proper materials, densities and thicknesses during
placement and compaction of compacted fill prior to placement of compacted
fill, inspect subgrade and verify that site has been prepared properly
Section 1705.6 “Soils” statement and Table 1705.6 indicate that it is
mandatory that a representative of this firm (responsible engineering firm),
perform observations and fill compaction testing during excavation operations
to verify that the remedial operations are consistent with the recommendations
presented in this report. All grading excavations resulting from the removal
of soils should be observed and evaluated by a representative of our firm
before they are backfilled.
Our firm should observe the bearing soils of the excavation bottoms (including
the bottom of the building pad undercut) and footing trench excavations of the
main structure and exterior structures such as retaining/site walls, and collect
soils samples to obtain and verify the maximum dry density of the on-site or
imported soils to be used as backfill material for the grading or retaining wall
backfill. Our firm should also perform field density tests of compacted soils
placed at least every 2 feet in thickness, verify the adequacy of the soil
moisture content and relative compaction.
In addition, our firm should verify the adequacy of imported soils by performing
sieve and expansion index tests, as well as maximum dry density tests and
optimum moisture tests; verify the compaction and moisture content of
subgrade soils to receive pavement or flatwork improvements; obtain soil
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samples and perform R-values for public street areas (if required to verify the
adequacy of pavement cross sections; and verify the compaction of the asphalt
concrete and the adequacy of the grain size for the base material.
B. Seismic Design Criteria
10. Seismic Data Bases: The estimation of the peak ground acceleration and the
repeatable high ground acceleration (RHGA) likely to occur at the site is based
on the known significant local and regional faults within 100 miles of the site.
11. Seismic Design Criteria: The proposed structure should be designed in
accordance with the 2019 CBC, which incorporates by reference the ASCE 7-
16 for seismic design. We have determined the mapped spectral acceleration
values for the site based on a latitude of 33.1470 degrees and a longitude
of -117.3425 degrees, utilizing a program titled “Seismic Design Map Tool” and
provided by the USGS through SEAOC, which provides a solution for ASCE 7-
16 utilizing digitized files for the Spectral Acceleration maps. See Appendix B.
12. Structure and Foundation Design: The design of the new structures and
foundations should be based on Seismic Design Category D, Risk Category II
for a Site Class C-Very Dense Soil and Soft Rock.
13. Spectral Acceleration and Design Values: The structural seismic design, when
applicable, should be based on the following values, which are based on the
site location, soil characteristics, and seismic maps by USGS, as required by
the 2019 CBC. The summarized seismic soil parameters are presented in Table
I below, have been calculated with the SEAOC Seismic Design Map Tool. The
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complete values are included in Appendix B. The Site Class C values for this
property are:
TABLE I
Mapped Spectral Acceleration Values and Design Parameters
SS S1 SMS SM1 SDS SD1 Fa Fv PGA PGAM SDC
1.098 0.396 1.317 0.594 0.878 0.396 1.2 1.5 0.486 0.583 D
C. Foundation Recommendations
14. Footings: We recommend that the proposed structures be supported on
conventional, individual-spread and/or continuous footing foundations bearing
on undisturbed formational materials or on properly compacted fill soils over
formational soils. No footings should be underlain by undocumented fill soils.
All building footings should be built on formational soils or properly compacted
fill prepared as recommended above in Recommendation Nos. 3, 4 and 5. The
footings should be founded at least 18 inches below the lowest adjacent
finished grade when founded into properly compacted fill or formational soils.
Footings located adjacent to utility trenches should have their bearing surfaces
situated below an imaginary 1.0:1.0 plane projected upward from the bottom
edge of the adjacent utility trench. Otherwise, the utility trenches should be
excavated farther from the footing locations.
Footings located adjacent to the tops of slopes should be extended sufficiently
deep so as to provide at least 8 feet of horizontal cover between the slope face
and outside edge of the footing at the footing bearing level.
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15. Bearing Values: At the recommended depths, footings on formational or
properly compacted fill soils may be designed for allowable bearing pressures
of 2,500 psf for combined dead and live loads and 3,325 psf for all loads,
including wind or seismic. The footings should, however, have a minimum
width of 15 inches. An increase in soil allowable static bearing can be used as
follows: 800 psf for each additional foot over 1.5 feet in depth and 400 psf for
each additional foot in width to a total not exceeding 4,000 psf. The static soil
bearing value may be increased one-third for seismic and wind load analysis.
As previously indicated, all of the foundations for the building should be built
on dense formational soils or properly compacted fill soils.
16. Footing Reinforcement: All continuous footings should contain top and bottom
reinforcement to provide structural continuity and to permit spanning of local
irregularities. We recommend that a minimum of two No. 5 top and two No.
5 bottom reinforcing bars be provided in the footings. All footings should be
reinforced as specified by the structural engineer. A minimum clearance of 3
inches should be maintained between steel reinforcement and the bottom or
sides of the footing. Isolated square footings should contain, as a minimum,
a grid of three No. 4 steel bars on 12-inch centers, both ways. In order for us
to offer an opinion as to whether the footings are founded on soils of sufficient
load bearing capacity, it is essential that our representative inspect the footing
excavations prior to the placement of reinforcing steel or forms.
NOTE: The project Civil/Structural Engineer should review all reinforcing
schedules. The reinforcing minimums recommended herein are not to be
construed as structural designs, but merely as minimum reinforcement to
reduce the potential for cracking and separations.
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17. Lateral Loads: Lateral load resistance for the structure supported on footing
foundations may be developed in friction between the foundation bottoms and
the supporting subgrade. An allowable friction coefficient of 0.35 is considered
applicable. An additional allowable passive resistance equal to an equivalent
fluid weight of 275 pounds per cubic foot (pcf) acting against the foundations
may be used in design provided the footings are poured neat against the dense
formational or properly compacted fill materials. These lateral resistance value
assume a level surface in front of the footing for a minimum distance of three
times the embedment depth of the footing and any shear keys, but not less
than 8 feet from a slope face, measured from effective top of foundation.
Retaining walls supporting surcharge loads or affected by upper foundations
should consider the effect of those upper loads.
18. Settlement: Settlements under structural design loads are expected to be
within tolerable limits for the proposed structures. For footings designed in
accordance with the recommendations presented in the preceding paragraphs,
we anticipate that the total and differential static settlement for the proposed
improvements will be on the order of 1 inch and approximately, post-
construction differential settlement angular rotation should be less than 1/240.
D. Concrete Slab On-Grade Criteria
Slabs on-grade may only be used on new, properly compacted fill or when bearing
on dense formational soils.
19. Minimum Floor Slab Thickness and Reinforcement: Based on our experience,
we have found that, for various reasons, floor slabs occasionally crack.
Therefore, we recommend that all slabs on-grade contain at least a minimum
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amount of reinforcing steel to reduce the separation of cracks, should they
occur. Slab subgrade soil should be verified by a Geotechnical Exploration,
Inc. representative to have the proper moisture content within 48 hours prior
to placement of the vapor barrier and pouring of concrete.
New interior floor slabs should be a minimum of 4-inches actual thickness and
be reinforced with No. 4 bars on 18-inch centers, both ways, placed at mid-
height in the slab. Soil moisture content should be kept above the optimum
prior to waterproofing placement under the new concrete slab. Shrinkage
joints should be specified by the structural engineer.
We note that shrinkage cracking can result in reflective cracking in brittle
flooring surfaces such as stone and tiles. It is imperative that if movement
intolerant flooring materials are to be utilized, the flooring contractor and/or
architect should provide specifications for the use of high-quality isolation
membrane products installed between slab and floor materials.
20. Slab Moisture Emission: Although it is not the responsibility of geotechnical
engineering firms to provide moisture protection recommendations, as a
service to our clients we provide the following discussion and suggested
minimum protection criteria. Actual recommendations should be provided by
the project architect and waterproofing consultants or product manufacturer.
It is recommended to contact the vapor barrier manufacturer to schedule a
pre-construction meeting and to coordinate a review, in-person or digital, of
the vapor barrier installation.
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Soil moisture vapor can result in damage to moisture-sensitive floors, some
floor sealers, or sensitive equipment in direct contact with the floor, in addition
to mold and staining on slabs, walls and carpets. The common practice in
Southern California is to place vapor retarders made of PVC, or of polyethylene.
PVC retarders are made in thickness ranging from 10- to 60-mil. Polyethylene
retarders, called visqueen, range from 5- to 10-mil in thickness. These
products are no longer considered adequate for moisture protection and can
actually deteriorate over time.
Specialty vapor retarding and barrier products possess higher tensile strength
and are more specifically designed for and intended to retard moisture
transmission into and through concrete slabs. The use of such products is
highly recommended for reduction of floor slab moisture emission.
The following American Society for Testing and Materials (ASTM) and American
Concrete Institute (ACI) sections address the issue of moisture transmission
into and through concrete slabs: ASTM E1745-17 Standard Specification for
Plastic Water Vapor Retarders Used in Contact Concrete Slabs; ASTM E1643-
18a Standard Practice for Selection, Design, Installation, and Inspection of
Water Vapor Retarders Used in Contact with Earth or Granular Fill Under
Concrete Slabs; ACI 302.2R-06 Guide for Concrete Slabs that Receive
Moisture-Sensitive Flooring Materials; and ACI 302.1R-15 Guide to Concrete
Floor and Slab Construction.
20.1 Based on the above, we recommend that the vapor barrier consist of a
minimum 15-mil extruded polyolefin plastic (no recycled content or
woven materials permitted). Permeance as tested before and after
mandatory conditioning (ASTM E1745 Section 7.1 and subparagraphs
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7.1.1-7.1.5) should be less than 0.01 perms (grains/square
foot/hour/per inch of Mercury) and comply with the ASTM E1745-17
Class A requirements. Installation of vapor barriers should be in
accordance with ASTM E1643-18a. The basis of design is 15-mil Stego
Wrap vapor barrier placed per the manufacturer’s guidelines. Reef
Industries Vapor Guard membrane has also been shown to achieve a
permeance of less than 0.01 perms. We recommend that the slab be
poured directly on the vapor barrier, which is placed directly on the
prepared properly compacted smooth subgrade soil surface.
20.2 Common to all acceptable products, vapor retarder/barrier joints must
be lapped at least 6 inches. Seam joints and permanent utility
penetrations should be sealed with the manufacturer’s recommended
tape or mastic. Edges of the vapor retarder should be extended to
terminate at a location in accordance with ASTM E1643-18a or to an
alternate location that is acceptable to the project’s structural engineer.
All terminated edges of the vapor retarder should be sealed to the
building foundation (grade beam, wall, or slab) using the manufacturer’s
recommended accessory for sealing the vapor retarder to pre-existing
or freshly placed concrete. Additionally, in actual practice, stakes are
often driven through the retarder material, equipment is dragged or
rolled across the retarder, overlapping or jointing is not properly
implemented, etc. All these construction deficiencies reduce the
retarder’s effectiveness. In no case should retarder/barrier products be
punctured or gaps be allowed to form prior to or during concrete
placement. Vapor barrier-safe screeding and forming systems should
be used that will not leave puncture holes in the vapor barrier, such as
Beast Foot (by Stego Industries) or equivalent.
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20.3 Vapor retarders/barriers do not provide full waterproofing for structures
constructed below free water surfaces. They are intended to help reduce
or prevent vapor transmission and/or capillary migration through the
soil and through the concrete slabs. Waterproofing systems must be
designed and properly constructed if full waterproofing is desired. The
owner and project designers should be consulted to determine the
specific level of protection required.
20.4 Following placement of any concrete floor slabs, sufficient drying time
must be allowed prior to placement of floor coverings. Premature
placement of floor coverings may result in degradation of adhesive
materials and loosening of the finish floor materials.
21. Exterior Slab Thickness and Reinforcement: As a minimum for protection of
on-site improvements, we recommend that all exterior pedestrian concrete
slabs be 4 inches thick and be founded on properly compacted and tested fill,
with No. 3 bars at 15-inch centers, both ways, at the center of the slab, and
contain adequate isolation and control joints. The performance of on-site
improvements can be greatly affected by soil base preparation and the quality
of construction. It is therefore important that all improvements are properly
designed and constructed for the existing soil conditions. The improvements
should not be built on loose soils or fills placed without our observation and
testing.
For exterior slabs with the minimum shrinkage reinforcement, control joints
should be placed at spaces no farther than 15 feet apart or the width of the
slab, whichever is less, and also at re-entrant corners. Control joints in
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exterior slabs should be sealed with elastomeric joint sealant. The sealant
should be inspected every 6 months and be properly maintained
E. Retaining Wall Design Criteria
22. Design Parameters – Unrestrained: The active earth pressure to be utilized in
the design of any cantilever site retaining walls, utilizing on-site low- expansive
[EI less than 50] or imported very low- to low-expansive soils [EI less than
50] as backfill should be based on an Equivalent Fluid Weight of 38 pcf (for
level backfill only). For 2.0:1.0 sloping backfill, the cantilever site retaining
walls should be designed with an equivalent fluid pressure of 52 pcf.
Unrestrained retaining walls should be backfilled with properly compacted very
low to low expansive soils. Unrestrained building retaining walls should be
designed for 38 pcf for level low expansive soil backfill, and use a conversion
load factor of 0.31 for vertical surcharge loads to be converted to uniform
lateral surcharge loads. Temporary cantilever shoring walls may use 45 pcf
active pressure, and a conversion factor of 0.36 to convert vertical uniform
surcharge to horizontal uniform pressure. For passive resistance, use the
value of 685 pcf times the diameter of the soldier pile, times the depth of
embedment below the grade excavation in front of the piles.
23. Design Parameters – Restrained: Temporary or permanent site restrained
shoring walls or restrained building retaining walls supporting low expansive
level backfill may utilize a triangular pressure increasing at a rate of 56 pcf for
wall design (78 pcf for sloping 2.0:1.0 backfill). The soil pressure produced by
any footings, improvements, or any other surcharge placed within a horizontal
distance equal to the height of the retaining portion of the wall should be
included in the wall design pressure. A conversion factor of 0.47 pcf may be
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used to convert vertical uniform surcharge loads to lateral uniform pressure
behind a restrained retaining wall with level backfill and 0.64 when supporting
a 2 to 1 sloping backfill. The recommended lateral soil pressures are based on
the assumption that no loose soils or unstable soil wedges will be retained by
the retaining wall. Backfill soils should consist of low-expansive soils with EI
less than 50, and should be placed from the heel of the foundation to the
ground surface within the wedge formed by a plane at 30 from vertical, and
passing by the heel of the foundation and the back face of the retaining wall.
24. Retaining Wall Seismic Design Pressures: For seismic design of unrestrained
walls over 6 feet in exposed height, we recommend that the seismic pressure
increment be taken as a fluid pressure distribution utilizing an equivalent fluid
weight of 16 pcf. This seismic increment is waived for restrained basement
walls. If the walls are designed as unrestrained walls, then the seismic load
should be added to the static soil pressure.
25. Basement/Retaining Wall Drainage: The preceding design pressures assume
that the walls are backfilled with properly compacted low expansion potential
materials (Expansion Index less than 50) and that there is sufficient drainage
behind the walls to prevent the build-up of hydrostatic pressures from surface
water infiltration. We recommend that drainage be provided by a composite
drainage material such as J-Drain 200/220 and J-Drain SWD, or equivalent.
No perforated pipes or gravel are utilized with the J-Drain system. The drain
material should terminate 12 inches below the exterior finish surface where
the surface is covered by slabs or 18 inches below the finish surface in
landscape areas (see Figure No. VI for Schematic Retaining Wall Subdrain
Recommendations). Waterproofing should extend from the bottom to the top
of the wall.
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Backfill placed behind retaining walls should be compacted to a minimum
degree of compaction of 90 percent using light compaction equipment. If
heavy equipment is used, the walls should be appropriately temporarily
braced. Crushed rock gravel may only be used as backfill in areas where
access is too narrow to place compacted soils. Behind shoring walls sand slurry
backfill may be used behind lagging.
Geotechnical Exploration, Inc. will assume no liability for damage to
structures or improvements that is attributable to poor drainage. The
architectural plans should clearly indicate that subdrains for any lower-level
walls be placed at an elevation at least 1 foot below the bottom of the lower-
level slabs.
F. Slopes
26. Temporary Slopes: Based on our subsurface investigation work, laboratory
test results, and engineering analysis, temporary cut slopes up to 12 feet in
height in the formational materials should be stable from mass instability at
an inclination 0.75 :1.0 (horizontal to vertical). Temporary cut slopes up to
12 feet in height in loose fill soils should be stable against mass instability at
an inclination of 1.5:1.0. In properly compacted fill soils, temporary slopes
should be stable at a slope ratio of 1.0 to 1.0.
Some localized sloughing or raveling of the soils exposed on the slopes may
occur. Since the stability of temporary construction slopes will depend largely
on the contractor's activities and safety precautions (storage and equipment
loadings near the tops of cut slopes, surface drainage provisions, etc.), it
should be the contractor's responsibility to establish and maintain all
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temporary construction slopes at a safe inclination appropriate to the methods
of operation. No soil stockpiles or surcharge may be placed within a horizontal
distance of 10 feet or the depth of the excavation, whichever is larger, from
the excavation top.
If these recommendations are not feasible due to space constraints, temporary
shoring may be required for safety and to protect adjacent property
improvements. Similarly, footings near temporary cuts should be underpinned
or protected with shoring.
26.1 Temporary Excavations: Temporary vertical excavation slots should be
executed in an “A-B-C” alternating slot method close to property lines. Slots
should not be taller than 3½ feet for new property line retaining walls. The
total slot width of the recommended slots should be no longer than 8 feet.
Other interior excavations deeper than 3 feet can be made at a 1.0:1.0 slope
ratio. Temporary excavations are anticipated at proposed retaining wall
locations shown on the grading plan.
27. Slope Observations: A representative of Geotechnical Exploration, Inc.
must observe any steep temporary slopes during construction. In the event
that soils and formational material comprising a slope are not as anticipated,
any required slope design changes would be presented at that time.
28. Permanent Slopes: Any new or existing cut or fill slopes up to 10 feet in height
should be constructed at an inclination of 2.0:1.0 (horizontal to vertical), be
provided with a keyway at least 2 feet in depth and at least 8 feet in width for
the entire length of the slope. Permanent slopes at a 2.0:1.0 slope ratio should
possess a factor of safety of 1.5 against deep and shallow failure.
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G. Pavements
29. Concrete Pavement: We recommend that driveways subject only to
automobile and light truck traffic be 5.5 inches thick and be supported directly
on properly prepared/compacted on-site subgrade soils. The upper 6 inches
of the subgrade below the slab should be compacted to a minimum degree of
compaction of 95 percent just prior to paving. The concrete should conform
to Section 201 of The Standard Specifications for Public Works Construction,
2015 Edition, for Class 560-C-3250.
In order to control shrinkage cracking, we recommend that saw-cut,
weakened-plane joints be provided at about 12-foot centers both ways and at
reentrant corners. The pavement slabs should be saw-cut as soon as practical
but no more than 24 hours after the placement of the concrete. The depth of
the joint should be one-quarter of the slab thickness and its width should not
exceed 0.02-foot. Reinforcing steel is not necessary unless it is desired to
increase the joint spacing recommended above.
30. Interlocking Permeable Pavers: If desired, we recommend that permeable
pavement pavers for the driveway, subject only to automobile and light truck
traffic, be supported on a 1.5 inches of bedding sand No. 8 on either a 6 inches
of Crushed Miscellaneous Base conforming to Section 200-2 of the Standard
Specifications for Public Works Construction (2018 Edition) or 6 inches of No.
57 crushed rock gravel per ASTM D448 gradation. The upper 6 inches of the
pavement subgrade soil as well as the aggregate base layer should be
compacted to a minimum degree of compaction of 95 percent. Preparation of
the subgrade and placement of the base materials should be performed under
the observation of our representative.
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H. Site Drainage Considerations
31. Erosion Control: Appropriate erosion control measures should be taken at all
times during and after construction to prevent surface runoff waters from
entering footing excavations or ponding on finished building pad areas.
32. Surface Drainage: Adequate measures should be taken to properly finish-
grade the lot after the structures and other improvements are in place.
Drainage waters from this site and adjacent properties should be directed away
from the footings, floor slabs, and slopes, onto the natural drainage direction
for this area or into properly designed and approved drainage facilities
provided by the project civil engineer. Roof gutters and downspouts should be
installed on the residence, with the runoff directed away from the foundations
via closed drainage lines. Proper subsurface and surface drainage will help
minimize the potential for waters to seek the level of the bearing soils under
the footings and floor slabs.
Failure to observe this recommendation could result in undermining and
possible differential settlement of the structure or other improvements on the
site or cause other moisture-related problems. Currently, the CBC requires a
minimum 1 percent surface gradient for proper drainage of building pads
unless waived by the building official. Concrete pavement may have a
minimum gradient of 0.5-percent.
33. Planter Drainage: Planter areas, flower beds and planter boxes should be
sloped to drain away from the footings and floor slabs at a gradient of at least
5 percent within 5 feet from the perimeter walls. Any planter areas adjacent
to the residence or surrounded by concrete improvements should be provided
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with sufficient area drains to help with rapid runoff disposal. No water should
be allowed to pond adjacent to the residence or other improvements or
anywhere on the site.
34. Drainage Quality Control: It must be understood that it is not within the scope
of our services to provide quality control oversight for surface or subsurface
drainage construction or retaining wall sealing and base of wall drain
construction. It is the responsibility of the contractor to verify proper wall
sealing, geofabric installation, protection board (if needed), drain depth below
interior floor or yard surface, pipe percent slope to the outlet, etc.
I. General Recommendations
35. Project Start Up Notification: In order to reduce work delays during site
development, this firm should be contacted 48 hours prior to any need for
observation of footing excavations or field density testing of compacted fill
soils. If possible, placement of formwork and steel reinforcement in footing
excavations should not occur prior to observing the excavations; in the event
that our observations reveal the need for deepening or re-designing foundation
structures at any locations, any formwork or steel reinforcement in the affected
footing excavation areas would have to be removed prior to correction of the
observed problem (i.e., deepening the footing excavation, recompacting soil
in the bottom of the excavation, etc.).
36. Cal-OSHA: Where not superseded by specific recommendations presented in
this report, trenches, excavations, and temporary slopes at the subject site
should be constructed in accordance with Title 8, Construction Safety Orders,
issued by Cal-OSHA.
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37. Construction Best Management Practices (BMPs): Construction BMPs must be
implemented in accordance with the requirements of the controlling
jurisdiction. Sufficient BMPs must be installed to prevent silt, mud or other
construction debris from being tracked into the adjacent street(s) or storm
water conveyance systems due to construction vehicles or any other
construction activity. The contractor is responsible for cleaning any such
debris that may be in the street at the end of each work day or after a storm
event that causes breach in the installed construction BMPs.
All stockpiles of uncompacted soil and/or building materials that are intended
to be left unprotected for a period greater than 7 days are to be provided with
erosion and sediment controls. Such soil must be protected each day when
the probability of rain is 40% or greater. A concrete washout should be
provided on all projects that propose the construction of any concrete
improvements that are to be poured in place. All erosion/sediment control
devices should be maintained in working order at all times. All slopes that are
created or disturbed by construction activity must be protected against erosion
and sediment transport at all times. The storage of all construction materials
and equipment must be protected against any potential release of pollutants
into the environment.
XI. GRADING NOTES
Geotechnical Exploration, Inc. recommends that we be retained to verify the
actual soil conditions revealed during site grading work and footing excavation to be
as anticipated in this "Updated Report of Preliminary Geotechnical Investigation" for
the project. In addition, the placement and compaction of any fill or backfill soils
during site grading work must be observed and tested by the soil engineer.
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It is the responsibility of the grading contractor and general contractor to comply with
the requirements on the grading plans as well as the local grading ordinance. All
retaining wall and trench backfill should be properly compacted. Geotechnical
Exploration, Inc. will assume no liability for damage occurring due to improperly or
uncompacted backfill placed without our observations and testing.
XII. LIMITATIONS
Our conclusions and recommendations have been based on available data obtained
from our field investigation and laboratory analysis, as well as our experience with
similar soils and formational materials located in this area of Carlsbad. Of necessity,
we must assume a certain degree of continuity between exploratory excavations
and/or natural exposures. It is, therefore, necessary that all observations,
conclusions, and recommendations be verified at the time grading operations begin
or when footing excavations are placed. In the event discrepancies are noted,
additional recommendations may be issued, if required.
The work performed and recommendations presented herein are the result of an
investigation and analysis that meet the contemporary standard of care in our
profession within the County of San Diego. No warranty is provided.
As stated previously, it is not within the scope of our services to provide quality
control oversight for surface or subsurface drainage construction or retaining wall
sealing and base of wall drain construction. It is the responsibility of the contractor
to verify proper wall sealing, geofabric installation, protection board installation (if
needed), drain depth below interior floor or yard surfaces; pipe percent slope to the
outlet, etc.
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This report should be considered valid for a period of two (2) years, and is subject to
review by our firm following that time. If significant modifications are made to the
building plans, especially with respect to the height and location of any proposed
structures, this report must be presented to us for immediate review and possible
revision.
It is the responsibility of the owner and/or developer to ensure that the
recommendations summarized in this report are carried out in the field operations
and that our recommendations for design of this project are incorporated in the
project plans. We should be retained to review the project plans once they are
available, to verify that our recommendations are adequately incorporated in the
plans. Additional or modified recommendations may be issued if warranted after plan
review.
This firm does not practice or consult in the field of safety engineering. We do not
direct the contractor's operations, and we cannot be responsible for the safety of
personnel other than our own on the site; the safety of others is the responsibility of
the contractor. The contractor should notify the owner if any of the recommended
actions presented herein are considered to be unsafe.
The firm of Geotechnical Exploration, Inc. shall not be held responsible for
changes to the physical condition of the property, such as addition of fill soils or
changing drainage patterns, which occur subsequent to issuance of this report and
the changes are made without our observations, testing, and approval.
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Once again, should any questions arise concerning this report, please feel free to
contact the undersigned. Reference to our Job No. 20-12942 will expedite a reply
to your inquiries.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________ ______________________________
Jaime A. Cerros, P.E. Hector G. Estrella
R.C.E. 34422/G.E. 2007 P.G. 9019/C.E.G. 2656
Senior Geotechnical Engineer
________________________________
Cathy K. Ganze, Project Geologist
REFERENCES
JOB NO. 20-12942
December 2021
2007 Working Group on California Earthquake Probabilities, 2008, The Uniform California Earthquake
Rupture Forecast, Version 2 (UCERF 2), U.S Geological Survey Open-file Report 2007-1437 and
California Geological Survey Special Report 203.
Association of Engineering Geologists, 1973, Geology and Earthquake Hazards, Planners Guide to the
Seismic Safety Element, Association of Engineering Geologists, Southern California Section.
Berger, V. and Schug, D.L., 1991, Probabilistic Evaluation of Seismic Hazard in the San Diego-Tijuana
Metropolitan Region, Environmental Perils, San Diego Region, Geological Society of America by the San
Diego Association of Geologists, October 20, 1991, p. 89-99.
Crowell, J.C., 1962, Displacement Along the San Andreas, Fault, California, Geological Society of
America, Special Papers, no. 71.
Demere, T.A. 1997, Geology of San Diego County, California, San Diego Natural History Museum,
http://archive.sdnhm.org/research/paleontology/sdgeol.html, accessed July 30, 2020.
Grant Ludwig, L.B. and Shearer, P.M., 2004, Activity of the Offshore Newport-Inglewood Rose Canyon
Fault Zone, Coastal Southern California, from Relocated Microseismicity. Bulletin of the Seismological
Society of America, 94(2), 747-752.
Greene, H.G., Bailey, K.A., Clarke, S.H., Ziony, J.I. and Kennedy, M.P., 1979, Implications of fault patterns of the inner California continental borderland between San Pedro and San Diego, in Abbott, P.L., and Elliot, W.J., eds., Earthquakes and other perils, San Diego region: San Diego Association of
Geologists, Geological Society of America field trip, p. 21–28.
Greensfelder, R.W., 1974, Maximum Credible Rock Accelerations from Earthquakes in California,
California Division of Mines and Geology.
Hart E.W. and Bryant, W.A., 1997, Fault-Rupture Hazard Zones in California, California Division of Mines
and Geology, Special Publication 42.
Hart, E.W., Smith, D.P. and Saul, R.B., 1979, Summary Report: Fault Evaluation Program, 1978 Area
(Peninsular Ranges-Salton Trough Region), California Division of Mines and Geology, Open-file Report
79-10 SF, 10.
Hauksson, E. and Jones, L.M., 1988, The July 1986 Oceanside (ML=5.3) Earthquake Sequence in the
Continental Borderland, Southern California Bulletin of the Seismological Society of America, v. 78, p. 1885-1906. Hileman, J.A., Allen, C.R. and Nordquist, J.M., 1973, Seismicity of the Southern California Region,
January 1, 1932 to December 31, 1972, Seismological Laboratory, Cal-Tech, Pasadena, California.
Kennedy, M.P. and Tan, S.S., 2007, Geologic Map of the Oceanside 30’x60’ Quadrangle, California,
California Geological Survey, Department of Conservation.
Richter, C.F., 1958, Elementary Seismology, W.H. Freeman and Company, San Francisco, California.
REFERENCES/Page 2
Rockwell, T.K., 2010, The Rose Canyon Fault Zone in San Diego, Proceedings of the Fifth International
Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, Paper No.
7.06C.
Rockwell, T.K., Dawson, T.E., Young Ben-Horin, J. and Seitz, G., 2014, A 21-Event, 4,000-Year History
of Surface Ruptures in the Anza Seismic Gap, San Jacinto Fault, and Implications for Long-term
Earthquake Production on a Major Plate Boundary Fault, Pure and Applied Geophysics, v. 172, 1143–
1165.
Rockwell, T.K., Millman, D.E., McElwain, R.S. and Lamar, D.L., 1985, Study of Seismic Activity by
Trenching Along the Glen Ivy North Fault, Elsinore Fault Zone, Southern California: Lamar-Merifield
Technical Report 85-1, U.S.G.S. Contract 14-08-0001-21376, 19 p.
Ross, Z.E., Hauksson E. and Ben-Zion Y., 2017, Abundant Off-fault Seismicity and Orthogonal Structures
in the San Jacinto Fault Zone, Science Advances, 2017; 3(3): e1601946.
Toppozada, T.R. and Parke, D.L., 1982, Areas Damaged by California Earthquakes, 1900-1949,
California Division of Mines and Geology, Open-file Report 82-17.
U.S. Dept. of Agriculture, 1953, Aerial Photographs AXN-14M-19 and 20.
VICINITY MAP
Garfield Street Condominiums
4008 Garfield Street
Carlsbad, CA.Figure No. I
Job No. 20-12942
SITE
Thomas Guide San Diego County Edition pg 1106-E7
Approximate Locationof Proposed StructureHP-5HP-4HP-3HP-2HP-1HP-5Qop6-7QafQop6-7QafQop6-7QafQop6-7QafQop6-7QafQopQaf6-7Old Paralic Deposits( units 6-7 ) GEOLOGIC LEGENDArtificial FillApproximate Locationof Exploratory Handpit20-12942-P5.aiREFERENCE: This Plot Plan was prepared from an existing undated GRADING PLAN providedPASCO LARET SUITER & ASSOCIATES and from on-site field reconnaissance performed by GEI.NOTE: This Plot Plan is not to be used for legalpurposes. Locations and dimensions are approximate.Actual property dimensions and locations of utilitiesmay be obtained from the Approved Building Plansor the “As-Built” Grading Plans.Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.Figure No. IIJob No. 20-12942Scale: 1” =5’(approximate) (Updated)PLOT PLAN ANDSITE SPECIFICGEOLOGIC MAPGARFIELD STREETCHINQUAPIN AVENUE(updated December 2021)LEGEND
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/WEATHERED OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Dense to very dense.
Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 1.5'
106.9
SM
SM
SM
1.2DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
JOB NUMBERSAMPLE
HP-1
DATE LOGGED
± 67' Mean Sea Level
IIIa
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 1.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes medium dense to dense.
-- 16% passing #200 sieve.
SILTY SANDSTONE. Dense to very dense.
Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes mottled, red-brown and light brown.
Bottom @ 4.5'
106.9
102.4
105.7
120.76.4
SM
SM
SM
2.3
2.5
2.2DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
5
JOB NUMBERSAMPLE
HP-2
DATE LOGGED
± 67' Mean Sea Level
IIIb
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 4.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Dense to very dense.Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 3.5'
105.6
SM
SM
SM
1.8DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
JOB NUMBERSAMPLE
HP-3
DATE LOGGED
± 64' Mean Sea Level
IIIc
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 3.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)-- becomes medium dense to dense.
SILTY SANDSTONE. Medium dense to dense.
Damp. Light tan.
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes very dense.
-- 16% passing #200 sieve.
Bottom @ 5'
102.6
SM
SM
SM
2.4DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
5
6
JOB NUMBERSAMPLE
HP-4
DATE LOGGED
± 61.5' Mean Sea Level
IIId
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
2
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Medium dense to dense.
Damp. Light tan.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 3.5'
SM
SM
SMDEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
JOB NUMBERSAMPLE
HP-5
DATE LOGGED
± 59' Mean Sea Level
IIIe
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 3.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
75
80
85
90
95
100
105
110
115
120
125
130
135
0 5 10 15 20 25 30 35 40 45
WATER CONTENT, %
MOISTURE-DENSITY RELATIONSHIP
TEST RESULTS
Maximum Dry Density
Optimum Water Content 6.4
Source of Material
Description of Material
DRY DENSITY, pcfSILTY SAND (SM), Brown
ASTM D1557 Method A
HP-2 @ 2.5'
120.7 PCF
%
Curves of 100% Saturationfor Specific Gravity Equal to:
2.80
2.70
2.60
Test Method
Expansion Index (EI)
Figure Number: IV
Job Name: Garfield Street Residential Project
Site Location: 4008 Garfield Street, Carlsbad, CA
Job Number: 20-12942COMPACTION + EI DARK GRID 12942 GARFIELD-RINCON.GPJ GEI FEB06.GDT 11/16/20
L A B O R A T O R Y R E P O R T
Telephone (619) 425-1993 Fax 425-7917 Established 1928
C L A R K S O N L A B O R A T O R Y A N D S U P P L Y I N C.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Sales Order Number: 50003
Account Number: GEOE.R5
To:
*-------------------------------------------------*
Geotechnical Exploration Inc.
7420 Trade Street
San Diego, Ca 92121
Attention: Hector Estrella
Laboratory Number: SO8034-1 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation:
*-------------------------------------------------*
One soil sample received on 11/30/20 at 12:30pm,
from Garfield marked as HP-2@2-4.
Division of Construction, Method for Estimating the Service Life of
Steel Culverts.
pH 7.2
Water Added (ml)Resistivity (ohm-cm)
10 12000
5 9500
5 7700
5 7000
5 5800
5 6000
5 6200
41 years to perforation for a 16 gauge metal culvert.
53 years to perforation for a 14 gauge metal culvert.
73 years to perforation for a 12 gauge metal culvert.
94 years to perforation for a 10 gauge metal culvert.
114 years to perforation for a 8 gauge metal culvert.
Water Soluble Sulfate Calif. Test 417 <0.003%
Water Soluble Chloride Calif. Test 422 0.003%
_______________
Rosa Bernal
RMB/dbb
Analysis By California Test 643, 1999, Department of Transportation
Date: December 9, 2020
Purchase Order Number: GARFIELD
Figure No. IVb
L A B O R A T O R Y R E P O R T
Telephone (619) 425-1993 Fax 425-7917 Established 1928
C L A R K S O N L A B O R A T O R Y A N D S U P P L Y I N C.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Date: December 9, 2020
Purchase Order Number: GARFIELD
Sales Order Number: 50003
Account Number: GEOE.R5
To:
*-------------------------------------------------*
Geotechnical Exploration Inc.
7420 Trade Street
San Diego, Ca 92121
Attention: Hector Estrella
Laboratory Number: SO8034-2 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation:
*-------------------------------------------------*
One soil sample received on 11/30/20 at 12:30pm,
from Garfield marked as HP-4@3-5.
Analysis By California Test 643, 1999, Department of Transportation
Division of Construction, Method for Estimating the Service Life of
Steel Culverts.
pH 6.9
Water Added (ml)Resistivity (ohm-cm)
10 27000
5 17000
5 13000
5 9800
5 8800
5 9100
5 9600
36 years to perforation for a 16 gauge metal culvert.
47 years to perforation for a 14 gauge metal culvert.
65 years to perforation for a 12 gauge metal culvert.
83 years to perforation for a 10 gauge metal culvert.
101 years to perforation for a 8 gauge metal culvert.
Water Soluble Sulfate Calif. Test 417 <0.003%
Water Soluble Chloride Calif. Test 422 0.001%
_______________
Rosa Bernal
RMB/dbb
Figure No. IVc
Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.SITEFigure No. V Job No. 20-12942EXCERPT FROMNovember 2020Garfield-Condos-2008-geo.aiPacificOcean
APPENDIX A
UNIFIED SOIL CLASSIFICATION CHART
SOIL DESCRIPTION
Coarse-grained (More than half of material is larger than a No. 200 sieve)
GRAVELS, CLEAN GRAVELS GW Well-graded gravels, gravel and sand mixtures, little
(More than half of coarse fraction or no fines.
is larger than No. 4 sieve size, but
smaller than 3”) GP Poorly graded gravels, gravel and sand mixtures, little
or no fines.
GRAVELS WITH FINES GC Clay gravels, poorly graded gravel-sand-silt mixtures
(Appreciable amount)
SANDS, CLEAN SANDS SW Well-graded sand, gravelly sands, little or no fines
(More than half of coarse fraction
is smaller than a No. 4 sieve) SP Poorly graded sands, gravelly sands, little or no fines. SANDS WITH FINES SM Silty sands, poorly graded sand and silty mixtures.
(Appreciable amount)
SC Clayey sands, poorly graded sand and clay mixtures.
Fine-grained (More than half of material is smaller than a No. 200 sieve)
SILTS AND CLAYS
Liquid Limit Less than 50 ML Inorganic silts and very fine sands, rock flour, sandy silt
and clayey-silt sand mixtures with a slight plasticity
CL Inorganic clays of low to medium plasticity, gravelly
clays, silty clays, clean clays.
OL Organic silts and organic silty clays of low plasticity.
Liquid Limit Greater than 50 MH Inorganic silts, micaceous or diatomaceous fine sandy
or silty soils, elastic silts.
CH Inorganic clays of high plasticity, fat clays.
OH Organic clays of medium to high plasticity.
HIGHLY ORGANIC SOILS PT Peat and other highly organic soils
4008 Garfield Street, Carlsbad, CA
Latitude, Longitude: 33.1470, -117.3425
Date 12/10/2021, 8:16:48 AM
Design Code Reference Document ASCE7-16
Risk Category II
Site Class C - Very Dense Soil and Soft Rock
Type Value Description
SS 1.098 MCER ground motion. (for 0.2 second period)
S1 0.396 MCER ground motion. (for 1.0s period)
SMS 1.317 Site-modified spectral acceleration value
SM1 0.594 Site-modified spectral acceleration value
SDS 0.878 Numeric seismic design value at 0.2 second SA
SD1 0.396 Numeric seismic design value at 1.0 second SA
Type Value Description
SDC D Seismic design category
Fa 1.2 Site amplification factor at 0.2 second
Fv 1.5 Site amplification factor at 1.0 second
PGA 0.486 MCEG peak ground acceleration
FPGA 1.2 Site amplification factor at PGA
PGAM 0.583 Site modified peak ground acceleration
TL 8 Long-period transition period in seconds
SsRT 1.098 Probabilistic risk-targeted ground motion. (0.2 second)
SsUH 1.231 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration
SsD 1.5 Factored deterministic acceleration value. (0.2 second)
S1RT 0.396 Probabilistic risk-targeted ground motion. (1.0 second)
S1UH 0.438 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration.
S1D 0.6 Factored deterministic acceleration value. (1.0 second)
PGAd 0.596 Factored deterministic acceleration value. (Peak Ground Acceleration)
CRS 0.892 Mapped value of the risk coefficient at short periods
CR1 0.904 Mapped value of the risk coefficient at a period of 1 s
DISCLAIMER
While the information presented on this website is believed to be correct, SEAOC /OSHPD and its sponsors and contributors assume no responsibility or
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for building code approval and interpretation for the building site described by latitude/longitude location in the search results of this website.
UPDATED REPORT OF PRELIMINARY GEOTECHNICAL
INVESTIGATION
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
JOB NO. 20-12942
15 December 2021
(Revised 25 January 2022)
Prepared for:
Rincon Homes
15 December 2021
(Revised 25 January 2022)
Rincon Homes Job No. 20-12942
5315 Avenida Encinitas, Suite 200
Carlsbad, CA 92008
Attn: Mr. Thomas St. Clair
Subject: Updated Report of Preliminary Geotechnical Investigation
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
Dear Mr. St. Clair:
Per the request of Mr. Bryan Knapp with Pasco Laret Suiter and as required by City
of Carlsbad third-party reviewer (Hetherington Engineering, Inc.), Geotechnical
Exploration, Inc. has updated the geotechnical investigation for the subject project.
The field work was performed on October 26, 2020. The original “Report of
Preliminary Geotechnical Investigation” is dated December 9, 2020.
If the conclusions and recommendations presented in this report are incorporated
into the design and construction of the proposed three-story, single-family residences
with attached garages, detached accessory dwelling units, and associated
improvements, it is our opinion that the site is suitable for the proposed project.
This opportunity to be of service is sincerely appreciated. Should you have any
questions concerning the following report, please do not hesitate to contact us.
Reference to our Job No. 20-12942 will expedite a response to your inquiries.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________
Jaime A. Cerros, P.E.
Senior Geotechnical Engineer
R.C.E. 34422/G.E. 2007
TABLE OF CONTENTS
I. PROJECT SUMMARY ............................................................................. 1
II. SCOPE OF WORK ................................................................................. 2
III. SITE DESCRIPTION .............................................................................. 2
IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING .............................. 3
V. LABORATORY TESTING & SOIL INFORMATION ......................................... 4
VI. REGIONAL GEOLOGIC DESCRIPTION ...................................................... 8
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION ................................... 13
VIII. GEOLOGIC HAZARDS ......................................................................... 15
A. Local and Regional Faults ............................................................ 15
B. Other Geologic Hazards .............................................................. 21
IX. GROUNDWATER ................................................................................ 24
X. CONCLUSIONS & RECOMMENDATIONS ................................................. 26
A. Preparation of Soils for Site Development ...................................... 28
B. Seismic Design Criteria ............................................................... 35
C. Foundation Recommendations ..................................................... 36
D. Concrete Slab On-Grade Criteria .................................................. 38
E. Retaining Wall Design Criteria ...................................................... 43
F. Slopes ...................................................................................... 45
G. Pavements ................................................................................ 47
H. Site Drainage Considerations ....................................................... 48
I. General Recommendations .......................................................... 49
XI. GRADING NOTES ............................................................................... 50
XII. LIMITATIONS .................................................................................... 51
REFERENCES
FIGURES
I. Vicinity Map
II. Updated Plot Plan and Site-Specific Geologic Map
IIIa-e. Exploratory Boring Logs and Laboratory Results
IVa-c. Laboratory Test Results
V. Geologic Map Excerpt and Legend
VI. Schematic Retaining Wall Subdrain Recommendations
APPENDICES
A. Unified Soil Classification System
B. ASCE Seismic Summary Report
UPDATED REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION
Proposed Garfield Street Homes
4008 Garfield Street
Carlsbad, California
JOB NO. 20-12942
The following report presents the findings and recommendations of Geotechnical
Exploration, Inc. for the subject project.
I. PROJECT SUMMARY
It is our understanding, based on our review of the available plans prepared by Kirk
Moeller Architects, Inc., and Pasco Laret Suiter and Associates (references), that the
existing two-story, split-level single-family residential structure and the existing one-
story building located to the northeastern portion of the property and associated
improvements are to be entirely demolished and replaced with three, 3-story, multi-
family structures with attached garages, 4- to 6-foot-high retaining walls, and
associated improvements. The new structures are to be constructed of standard-
type building materials utilizing conventional foundations with concrete slab on-
grade. Foundation loads are expected to be typical for this type of relatively light
construction. A preliminary site plan by Kirk Moeller Architects, Inc., dated August
17, 2020, has been reviewed by us and used to understand the scope of the project.
When final plans are completed, they should be made available for our review.
Additional or modified recommendations will be provided at that time if warranted.
This updated report has been prepared to incorporate comments response to the city
third-party reviewer.
Based on the available information at this stage, it is our opinion that the proposed
site development would not destabilize neighboring properties or induce the
settlement of adjacent structures or improvements if designed and constructed in
accordance with our recommendations.
Garfield Street Homes Job No. 20-12942
Carlsbad, California Page 2
II. SCOPE OF WORK
The scope of work performed for this investigation included a site reconnaissance and
subsurface exploration program under the direction of our geologist with placement,
logging and sampling of five exploratory trenches, review of available published
information pertaining to the site geology, laboratory testing, geotechnical
engineering analysis of the field and laboratory data, and the preparation of this
report. The data obtained and the analyses performed were for the purpose of
providing design and construction criteria for the project earthwork, building
foundations, retaining walls, slab on-grade floors and associated improvements.
III. SITE DESCRIPTION
The lot is known as Assessor’s Parcel No. 206-080-01-00, with a current address of
4008 Garfield Street in the City of Carlsbad, County of San Diego, State of California.
Refer to Figure No. I, Vicinity Map, for the site location.
The square footage of the rectangular-shaped lot is reported in the referenced plans
as 6,001 square feet (0.14 AC). The property is bordered on the north by Chinquapin
Avenue, on the west by Garfield Street, and on the east and south by two single-
family residential structures. Refer to Figure No. II, Updated Plot Plan and Site-
Specific Geologic Map. The plot plan has been updated to include surveyed
information.
The existing property is currently developed with a two-story, split-level, single-
family residential structure and an existing one-story building located on the
northeastern portion of the property, landscape areas and associated improvements.
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Vegetation on the site primarily consists of an ornamental garden, shrubbery, weeds,
grasses and mature trees.
The property slopes down from the western property line to the eastern property line.
Approximate elevations across the property range from approximately +59 feet
above Mean Sea Level (MSL) along the eastern side of the site to approximately +67
feet above MSL at the western portion of the property. Survey information
concerning elevations across the site was obtained from the topographic survey
template of the preliminary site plan by Pasco Laret Suiter, dated August 03, 2020.
IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING
The field investigation was conducted on October 26, 2020, and consisted of surface
reconnaissance and a subsurface exploration program utilizing hand-excavated
exploratory test trenches to investigate and sample the subsurface soils. Five (5)
exploratory trenches (HP-1 to HP-5) were excavated to a maximum depth of 5 feet
in the areas of the proposed development and associated improvements. The
excavations revealed that the building site is underlain by approximately 6 inches of
loose to medium dense, silty sand fill soil over medium dense, silty sand natural
residual soil, mantling medium dense to dense formational materials. The soils
encountered in the exploratory trenches are considered to have a low expansion
potential with an Expansion Index of less than 50. The exploratory excavations were
continuously logged in the field by our geologist and described in accordance with
the Unified Soil Classification System (refer to Appendix A). The approximate
locations of the exploratory trenches are shown on Figure No. II, Updated Plot Plan
and Site-Specific Geologic Map.
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Representative samples were obtained from the exploratory trenches at selected
depths appropriate to the investigation. Relatively undisturbed chunk and drive
samples and disturbed bulk samples were collected from the exploratory trenches to
aid in classification and for appropriate laboratory testing. The samples were
returned to our laboratory for evaluation and testing. Exploratory trench logs have
been prepared on the basis of our observations and laboratory test results, and are
attached as Figure Nos. IIIa-e.
The exploratory trench logs and related information depict subsurface conditions only
at the specific locations shown on the plot plan and on the particular date designated
on the logs. Subsurface conditions at other locations may differ from conditions
occurring at the locations. Also, the passage of time may result in changes in
subsurface conditions due to environmental changes.
V. LABORATORY TESTING & SOIL INFORMATION
Laboratory tests were performed on retrieved soil samples in order to evaluate their
physical and mechanical properties. The test results are presented on Figure Nos.
IIIa-e and IVa-c. The following tests were conducted on representative soil samples:
1. Moisture Content (ASTM D2216-19)
2. Density Measurements (ASTM D2937-17e2)
3. Standard Test Method for Bulk Specific Gravity and Density of Com-
pacted Bituminous Mixtures using Coated Samples (ASTM D1188-07)
4. Laboratory Compaction Characteristics (ASTM D1557-12e1)
5. Determination of Percentage of Particles Smaller than #200
Sieve (ASTM D1140-17)
6. Resistivity and pH Analysis (Department of Transportation
California Test 643)
7. Water Soluble Sulfate (Dept of Transportation California Test 417)
8. Water Soluble Chloride (Dept of Transportation California Test 422)
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Moisture content and density measurements were performed by ASTM methods
D2216-19 and D2937-17e2 respectively, in conjunction with D1188-07 to establish
the in-situ moisture and density of samples retrieved from the exploratory trenches.
Measurements were also performed by ASTM method D1188-07, the bulk specific
gravity utilizing paraffin-coated specimens. This method helps to establish the in-
situ density of chunk samples retrieved from formational exposures/outcrops. The
test results are presented on the trench logs at the appropriate sample depths and
laboratory test results.
Laboratory compaction values (ASTM D1557-12e1) establish the optimum moisture
content and the laboratory maximum dry density of the tested soils. The relationship
between the moisture and density of remolded soil samples helps to establish the
relative compaction of the existing fill soils and soil compaction conditions to be
anticipated during any future grading operation. The test results are presented on
the trench logs at the appropriate sample depths and laboratory test results.
The particle size smaller than a No. 200 sieve analysis (ASTM D1140-17) aids in
classifying the tested soils in accordance with the Unified Soil Classification System
and provides qualitative information related to engineering characteristics such as
expansion potential, permeability, and shear strength. Our laboratory testing
indicated 16 percent of the sample passing the No. 200 sieve. The test results are
presented on the trench logs at the appropriate sample depths and laboratory test
results.
The expansion potential of soils is determined, when necessary, utilizing the Standard
Test Method for Expansion Index of Soils (ASTM D4829-19). In accordance with the
Standard (Table 5.3), potentially expansive soils are classified as follows:
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EXPANSION INDEX POTENTIAL EXPANSION
0 to 20 Very low
21 to 50 Low
51 to 90 Medium
91 to 130 High
Above 130 Very high
We performed expansion index tests on two soil samples retrieved from the site after
our original geotechnical report was issued, as requested by the third-party reviewer.
One sample was from the western half of the site and the other from the eastern half
of the site. The test results yielded an expansion index of 2 for the western half and
3 for the eastern half. Therefore, the soils can be classified as having a very low
expansion potential. Special recommendations are not required for the foundations
or slabs on-grade due to soil expansivity.
To assess soil corrosivity of the on-site soils, resistivity, pH, chloride and soluble
sulfate tests were performed by an outside consultant (Clarkson Laboratory and
Supply Inc.) on samples of the near surface soils most likely to be in contact with
concrete and ferrous metals. The most common factor in determining soils corrosivity
to ferrous metals is electrical resistivity. As soils’ resistivity decreases, its corrosivity
to ferrous metals increases. The tested soils yielded low resistivities of 8,800 and
5,800 Ohm-cm, indicating that the soils are mildly corrosive to ferrous metals.
Soils and fluids are considered neutral when pH is measured at 7, acidic when pH is
measured at <7 and alkaline when measured at >7. Soils are considered corrosive
when the pH gets down to around 5.5 or less. Results of the laboratory testing
yielded pH values of 7.2 and 6.9, indicating that the tested soils range from slightly
acid to slightly alkaline, indicating that pH is not a significant factor in soil corrosivity
to metals.
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Large concentrations of chlorides will adversely affect any ferrous metals such as iron
and steel. Soil with a chloride concentration greater than or equal to 500 ppm (0.05
percent) or more is considered corrosive to ferrous metals. The chloride content of the
tested soils measured at approximately 30 and 10 ppm or 0.003 and 0.0010 percent
respectively, indicating that chloride is not a major factor in corrosion to ferrous
metals.
The primary cause of deterioration of concrete in foundations and other below ground
structures is the corrosive attack by soluble sulfates present in the soil and
groundwater. The results of water-soluble sulfate testing performed on a
representative sample of the near surface soils in the general area of the proposed
structures, yielded soluble sulfate contents of less than 30 ppm or 0.003 percent,
indicating that the proposed cement-concrete structures that are in contact with the
underlying soils are anticipated to be affected with a negligible sulfate exposure. As
such, there is no restriction on selection of cement type.
The table below summarizes the laboratory results for chemical testing of the
sampled soils:
Sample Location/
Depth (ft) pH Soluble Sulfate
(PPM)
Soluble
Chloride
(PPM)
Soil Resistivity
(Ohm-cm)
HP-2 / 2.0-4.0 7.2 <30 30 5,800
HP-4 / 3.0-5.0 6.9 <30 10 8,800
The laboratory testing results are presented in Figure Nos. IVa-c. It should be noted
that Geotechnical Exploration Inc., does not practice corrosion engineering and
our assessment here should be construed as an aid to the owner or owner’s
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representative. A corrosion specialist should be consulted for any specific design
requirement.
Based on the field and laboratory test data, our observations of the primary soil types,
and our previous experience with laboratory testing of similar soils, our Geotechnical
Engineer has assigned values for friction angle, coefficient of friction, and cohesion
for those soils that will have significant lateral support or load bearing functions on
the project. The assumed soil strength values were utilized in determining the
recommended bearing value as well as active and passive earth pressure design
criteria for foundations and retaining walls. The assumed strength values for properly
compacted fill and for dense formational soils are 33 degrees and cohesion equal to
50 psf, as well as total unit weight of 120 pcf are based on the visual inspection of
the soils and our experience. With these values we calculated the ultimate bearing
capacity of the soil to be 9,285 psf by Terzaghi’s equation. This value was reduced
with a factor of safety of 3 to calculate the allowable bearing capacity of 3,095 psf,
which has been reduced to the nominal recommended value of 2,500 psf. The active
and passive pressure of the soils were calculated with Terzaghi’s equations for those
pressures and neglecting the cohesion contribution to values of 35.4 pcf and 407 pcf.
We have increased the active soil pressure to 38 pcf, and the passive soil pressure
was reduced to 275 pcf. The calculated friction coefficient of 0.649 has been reduced
to an allowable value of 0.35.
VI. REGIONAL GEOLOGIC DESCRIPTION
San Diego County has been divided into three major geomorphic provinces: The
Coastal Plain, the Peninsular Ranges and the Salton Trough. The Coastal Plain exists
west of the Peninsular Ranges. The Salton Trough is east of the Peninsular Ranges.
These divisions are the result of the basic geologic distinctions between the areas.
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Mesozoic metavolcanic, metasedimentary and plutonic rocks predominate in the
Peninsular Ranges with primarily Cenozoic sedimentary rocks to the west and east of
this central mountain range (Demere, 1997).
In the Coastal Plain region, where the subject property is located, the “basement”
consists of Mesozoic crystalline rocks. Basement rocks are also exposed as high relief
areas (e.g., Black Mountain northeast of the subject property and Cowles Mountain
near the San Carlos area of San Diego). Younger Cretaceous and Tertiary sediments
lap up against these older features. These sediments form a “layer cake” sequence
of marine and non-marine sedimentary rock units, with some formations up to 140
million years old. Faulting related to the La Nación and Rose Canyon Fault zones has
broken up this sequence into a number of distinct fault blocks in the southwestern
part of the county. Northwestern portions of the county are relatively undeformed
by faulting (Demere, 1997).
The Peninsular Range form the granitic spine of San Diego County. These rocks are
primarily plutonic, forming at depth beneath the earth’s crust 140 to 90 million years
ago as the result of the subduction of an oceanic crustal plate beneath the North
American continent. These rocks formed the much larger Southern California
batholith. Metamorphism associated with the intrusion of these great granitic masses
affected the much older sediments that existed near the surface over that period of
time. These metasedimentary rocks remain as roof pendants of marble, schist, slate,
quartzite and gneiss throughout the Peninsular Ranges. Locally, Miocene-age
volcanic rocks and flows have also accumulated within these mountains (e.g.,
Jacumba Valley). Regional tectonic forces and erosion over time have uplifted and
unroofed these granitic rocks to expose them at the surface (Demere, 1997).
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The Salton Trough is the northerly extension of the Gulf of California. This zone is
undergoing active deformation related to faulting along the Elsinore and San Jacinto
Fault Zones, which are part of the major regional tectonic feature in the southwestern
portion of California, the San Andreas Fault Zone. Translational movement along
these fault zones has resulted in crustal rifting and subsidence. The Salton Trough,
also referred to as the Colorado Desert, has been filled with sediments to depth of
approximately 5 miles since the movement began in the early Miocene, 24 million
years ago. The source of these sediments has been the local mountains as well as
the ancestral and modern Colorado River (Demere, 1997).
As indicated previously, the San Diego area is part of a seismically active region of
California. It is on the eastern boundary of the Southern California Continental
Borderland, part of the Peninsular Ranges Geomorphic Province. This region is part
of a broad tectonic boundary between the North American and Pacific Plates. The
actual plate boundary is characterized by a complex system of active, major, right-
lateral strike-slip faults, trending northwest/southeast. This fault system extends
eastward to the San Andreas Fault (approximately 70 miles from San Diego) and
westward to the San Clemente Fault (approximately 50 miles off-shore from San
Diego) (Berger and Schug, 1991).
In California, major earthquakes can generally be correlated with movement on
active faults. As defined by the California Division of Mines and Geology, now the
California Geological Survey, an "active" fault is one that has had ground surface
displacement within Holocene time, about the last 11,000 years (Hart and Bryant,
1997). Additionally, faults along which major historical earthquakes have occurred
(about the last 210 years in California) are also considered to be active (Association
of Engineering Geologist, 1973). The California Division of Mines and Geology defines
a "potentially active" fault as one that has had ground surface displacement during
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Quaternary time, that is, between 11,000 and 1.6 million years (Hart and Bryant,
1997).
During recent history, prior to April 2010, the San Diego County area has been
relatively quiet seismically. No fault ruptures or major earthquakes had been
experienced in historic time within the greater San Diego area. Since earthquakes
have been recorded by instruments (since the 1930s), the San Diego area has
experienced scattered seismic events with Richter magnitudes generally less than
M4.0. During June 1985, a series of small earthquakes occurred beneath San Diego
Bay, three of which were recorded at M4.0 to M4.2. In addition, the Oceanside
earthquake of July 13, 1986, located approximately 26 miles offshore of the City of
Oceanside, had a magnitude of M5.3 (Hauksson and Jones, 1988).
On June 15, 2004, a M5.3 earthquake occurred approximately 45 miles southwest of
downtown San Diego (26 miles west of Rosarito, Mexico). Although this earthquake
was widely felt, no significant damage was reported. Another widely felt earthquake
on a distant southern California fault was a M5.4 event that took place on July 29,
2008, west-southwest of the Chino Hills area of Riverside County.
Several earthquakes ranging from M5.0 to M6.0 occurred in northern Baja California,
centered in the Gulf of California on August 3, 2009. These were felt in San Diego
but no injuries or damage was reported. A M5.8 earthquake followed by a M4.9
aftershock occurred on December 30, 2009, centered about 20 miles south of the
Mexican border city of Mexicali. These were also felt in San Diego, swaying high-rise
buildings, but again no significant damage or injuries were reported.
On April 4, 2010, a large earthquake occurred in Baja California, Mexico. It was
widely felt throughout the southwest including Phoenix, Arizona and San Diego in
California. This M7.2 event, the Sierra El Mayor earthquake, occurred in northern
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Baja California, approximately 40 miles south of the Mexico-USA border at shallow
depth along the principal plate boundary between the North American and Pacific
plates. According to the U. S. Geological Survey this is an area with a high level of
historical seismicity, and it has recently also been seismically active, although this is
the largest event to strike in this area since 1892. The April 4, 2010, earthquake
appears to have been larger than the M6.9 earthquake in 1940 or any of the early
20th century events (e.g., 1915 and 1934) in this region of northern Baja California.
The event caused widespread damage to structures, closure of businesses,
government offices and schools, power outages, displacement of people from their
homes and injuries in the nearby major metropolitan areas of Mexicali in Mexico and
Calexico in Southern California.
This event's aftershock zone extends significantly to the northwest, overlapping with
the portion of the fault system that is thought to have ruptured in 1892. Some
structures in the San Diego area experienced minor damage and there were some
injuries. Ground motions for the April 4, 2010, main event, recorded at stations in
San Diego and reported by the California Strong Motion Instrumentation Program
(CSMIP), ranged up to 0.058g.
On July 7, 2010, a M5.4 earthquake occurred in Southern California at 4:53 pm
(Pacific Time) about 30 miles south of Palm Springs, 25 miles southwest of Indio, and
13 miles north-northwest of Borrego Springs. The earthquake occurred near the
Coyote Creek segment of the San Jacinto Fault. The earthquake exhibited right
lateral slip to the northwest, consistent with the direction of movement on the San
Jacinto Fault. The earthquake was felt throughout Southern California, with strong
shaking near the epicenter. It was followed by more than 60 aftershocks of M1.3
and greater during the first hour.
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In the last 50 years, there have been four other earthquakes in the magnitude M5.0
range within 20 kilometers of the Coyote Creek segment: M5.8 in 1968, M5.3 on
2/25/1980, M5.0 on 10/31/2001, and M5.2 on 6/12/2005. The biggest earthquake
near this location was the M6.0 Buck Ridge earthquake on 3/25/1937.
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION
Our field investigation, reconnaissance and review of the geologic map by Kennedy
and Tan, 2007, “Geologic Map of the Oceanside 30’x60’ Quadrangle, California”
indicate that the site is underlain at depth by late to middle Pleistocene-Aged Old
Paralic Deposits, Units 6-7 (Qop6-7) formational materials. An excerpt of the
geological map is included as Figure No. V. Our exploratory trenches indicate the
formational materials are overlain across the site by artificial fill soils (Qaf) and
subsoil/residual soil. Site-specific geology is mapped on Figure No. II, the Updated
Plot Plan and Site-Specific Geologic Map.
Fill Soil (Qaf): Our site investigation indicates that the areas in the general vicinity
of our exploratory trenches at the site are overlain by up to 12 inches of fill soil. The
encountered fill soil consists of fine- to medium-grained, dry to moist, gray-brown to
red-brown to brown, silty sands (SM) with variable amounts of roots. The fill soils
are generally loose. In our opinion, due to the variable density and poor condition of
the fill soil, it is not considered suitable in its current condition to support loads from
structures or additional fill. Refer to Figure Nos. IIIa-e for details.
Residual Soil/Subsoil: Residual soil/subsoil was encountered underlying the fill soils
in all the exploratory trenches. The approximate thickness of these soils was
observed to vary from approximately 6 inches to 3 feet in thickness. These soils
were noted to consist mainly of damp, light-brown, silty sands (SM). This material
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was observed to be generally loose to medium dense, porous and with some deeper
roots. In our opinion, due to the low density and potential compressibility of these
porous soils, these residual soils are not considered suitable to support loads from
structures or additional fill in their current condition. Refer to Figure Nos. IIIa-e for
details.
Old Paralic Deposits, Unit 6-7 (Qop6-7): The encountered formational materials are
described in the literature as Quaternary (late to middle Pleistocene Old Paralic
Deposits, Units 6-7. These formational materials were encountered in all trenches
underlying the residual soil at variable depths from 1 to 2.5 feet. The formational
materials consist of fine- to medium-grained, damp to moist, red-brown silty sands
(SM) with areas of moderate cementation and some deeper roots. The formational
materials underlying the site are dense to very dense. In our opinion, the dense to
very dense nature of the Old Paralic Deposits, Units 6-7, makes it suitable in its
current condition to support loads from structures or additional fill. Refer to Figure
Nos. IIIa-e for details.
Based on our review of the “Geologic Map of the Oceanside 30’x60’ Quadrangle,
California” by Kennedy and Tan, 2007, the Old Paralic Deposits, Units 6-7,
formational materials underlie the entire site at depth. The aforementioned Old
Paralic Deposit Units are described as “Poorly sorted, moderately permeable, reddish-
brown, interfingered strandline, beach, estuarine and colluvial deposits composed of
siltstone, sandstone and conglomerate.” According to the map, there are no faults
known to pass through the site (refer to Figure No. V, Geologic Map Excerpt and
Legend).
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VIII. GEOLOGIC HAZARDS
The following is a discussion of the geologic conditions and hazards common to this
area of Carlsbad, as well as project-specific geologic information relating to
development of the subject site.
A. Local and Regional Faults
Reference to the Geologic Map and Legend, Figure No. V (Kennedy and Tan, 2007),
indicates that no faults are shown to cross the site. Furthermore, our site
reconnaissance presented no indications of faulting crossing the site. In our
professional opinion, neither an active fault nor a potentially active fault underlies
the site.
A brief description of the nearby active faults including distances from the mapped
fault to the subject site at the closest point (based on the USGS Earthquake Hazards-
Interactive Fault Map), is presented below:
Newport-Inglewood-Rose Canyon Fault Zone System: The Oceanside section of the
Newport-Inglewood-Rose Canyon Fault Zone is mapped approximately 4.3 miles
west-southwest of the site. The offshore portion of the Newport-Inglewood Fault
Zone is described as a right-lateral, local reverse slip associated with fault steps
(SCEDC, 2020). The reported length is 46.2 miles extending in a northwest-
southeast direction. Surface trace is discontinuous in the Los Angeles Basin, but the
fault zone can easily be noted there by the existence of a chain of low hills extending
from Culver City to Signal Hill. South of Signal Hill, it roughly parallels the coastline
until just south of Newport Bay, where it heads offshore, and becomes the Newport-
Inglewood - Rose Canyon Fault Zone. A significant earthquake (M6.4) occurred along
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this fault on March 10, 1933. Since then, no additional significant events have
occurred. The fault is believed to have a slip rate of approximately 0.6-mm/yr with
an unknown recurrence interval. This fault is believed capable of producing an
earthquake of M6.0 to M7.4 (Grant Ludwig and Shearer, 2004).
Rose Canyon Fault Zone: The Rose Canyon Fault Zone is the southern section of the
Newport-Inglewood-Rose Canyon Fault Zone system mapped in the San Diego
County area as trending north-northwest to south-southeast from Oceanside to La
Jolla and generally north-south into San Diego Bay, through Coronado and offshore
downtown San Diego, from where it appears to head southward. The Rose Canyon
Fault Zone system is considered to be a complex zone of onshore and offshore, en
echelon right lateral, strike slip, oblique reverse, and oblique normal faults. This fault
is considered to be capable of generating an M7.2 earthquake and is considered
microseismically active, although no significant recent earthquakes since 1769 are
known to have occurred on the fault.
Investigative work on faults that are part of the Rose Canyon Fault Zone at the Police
Administration and Technical Center in downtown San Diego, at the SDG&E facility in
Rose Canyon, and within San Diego Bay and elsewhere within downtown San Diego,
has encountered offsets in Holocene (geologically recent) sediments. These findings
confirm Holocene displacement on the Rose Canyon Fault, which was designated an
“active” fault in November 1991 (Hart and Bryant, 1997).
Rockwell (2010) has suggested that the Rose CFZ underwent a cluster of activity
including 5 major earthquakes in the early Holocene, with a long period of inactivity
following, suggesting major earthquakes on the RCFZ behaves in a cluster-mode,
where earthquake recurrence is clustered in time rather than in a consistent
recurrence interval. With the most recent earthquake (MRE) nearly 500 years ago,
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it is suggested that a period of earthquake activity on the RCFZ may have begun.
Rockwell (2010) and a compilation of the latest research implies a long-term slip rate
of approximately 1 to 2 mm/year.
Coronado Bank Fault: The Coronado Bank Fault is located approximately 22.6 miles
southwest of the site. Evidence for this fault is based upon geophysical data (acoustic
profiles) and the general alignment of epicenters of recorded seismic activity (Greene
et al., 1979). The Oceanside earthquake of M5.3 recorded July 13, 1986, is known
to have been centered on the fault or within the Coronado Bank Fault Zone. Although
this fault is considered active, due to the seismicity within the fault zone, it is
significantly less active seismically than the Elsinore Fault (Hileman et al., 1973). It
is postulated that the Coronado Bank Fault is capable of generating a M7.6
earthquake and is of great interest due to its close proximity to the greater San Diego
metropolitan area.
San Diego Trough Fault Zone: The San Diego Trough Fault Zone is mapped
approximately 29.6 miles west-southwest of the site at its closest point. This fault is
described as a right-lateral type fault with a length of at least 93.2 miles and a slip
rate of roughly 1.5 mm/yr. The most recent surface rupture is of Holocene age
(SCEDC, 2020).
San Clemente Fault Zone: The San Clemente Fault Zone is mapped at approximately
56 miles southwest of the site at its closest point. This fault is described as a right-
lateral and vertical offsets type fault with a length of at least 130.5 miles described
as essentially continuous with the San Isidro fault zone, off the coast of Mexico and
a slip rate of roughly 1.5 mm/yr. The most recent surface rupture is of Holocene age
(SCEDC, 2020).
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Elsinore Fault: The Temecula and Julian sections of the Elsinore Fault Zone are
located approximately 23.5 and 33 miles northeast and east of the site, respectively.
The Elsinore Fault Zone extends approximately 125 miles from the Mexican border
to the northern end of the Santa Ana Mountains. The Elsinore Fault zone is a 1- to
4-mile-wide, northwest-southeast-trending zone of discontinuous and en echelon
faults extending through portions of Orange, Riverside, San Diego, and Imperial
Counties. Individual faults within the Elsinore Fault Zone range from less than 1 mile
to 16 miles in length. The trend, length and geomorphic expression of the Elsinore
Fault Zone identify it as being a part of the highly active San Andreas Fault system.
Like the other faults in the San Andreas system, the Elsinore Fault is a transverse
fault showing predominantly right-lateral movement. According to Hart et al. (1979),
this movement averages less than 1 centimeter per year. Along most of its length,
the Elsinore Fault Zone is marked by a bold topographic expression consisting of
linearly aligned ridges, swales and hallows. Faulted Holocene alluvial deposits
(believed to be less than 11,000 years old) found along several segments of the fault
zone suggest that at least part of the zone is currently active.
Although the Elsinore Fault Zone belongs to the San Andreas set of active, northwest-
trending, right-slip faults in the southern California area (Crowell, 1962), it has not
been the site of a major earthquake in historic time, other than a M6.0 earthquake
near the town of Elsinore in 1910 (Richter, 1958; Toppozada and Parke, 1982).
However, based on length and evidence of late-Pleistocene or Holocene displacement,
Greensfelder (1974) has estimated that the Elsinore Fault Zone is reasonably capable
of generating an earthquake with a magnitude as large as M7.5. Study and logging
of exposures in trenches placed in Glen Ivy Marsh across the Glen Ivy North Fault (a
strand of the Elsinore Fault Zone between Corona and Lake Elsinore), suggest a
maximum earthquake recurrence interval of 300 years, and when combined with
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previous estimates of the long-term horizontal slip rate of 0.8 to 7.0 mm/year,
suggest typical earthquake magnitudes of M6.0 to M7.0 (Rockwell et al., 1985). The
Working Group on California Earthquake Probabilities (2008) has estimated that there
is a 11 percent probability that an earthquake of M6.7 or greater will occur within 30
years on this fault.
San Jacinto Fault: The San Jacinto Fault is located approximately 46 to 66 miles
northeast of the site. The San Jacinto Fault Zone consists of a series of closely spaced
faults, including the Coyote Creek Fault, that form the western margin of the San
Jacinto Mountains. The fault zone extends from its junction with the San Andreas
Fault in San Bernardino, southeasterly toward the Brawley area, where it continues
south of the international border as the Imperial Transform Fault (Rockwell et al.,
2014).
The San Jacinto Fault zone has a high level of historical seismic activity, with at least
10 damaging earthquakes (M6.0 to M7.0) having occurred on this fault zone between
1890 and 1986. Earthquakes on the San Jacinto Fault in 1899 and 1918 caused
fatalities in the Riverside County area. Offset across this fault is predominantly right-
lateral, similar to the San Andreas Fault, although some investigators have suggested
that dip-slip motion contributes up to 10% of the net slip (Ross et al., 2017).
The segments of the San Jacinto Fault that are of most concern to major metropolitan
areas are the San Bernardino, San Jacinto Valley and Anza segments. Fault slip rates
on the various segments of the San Jacinto are less well constrained than for the San
Andreas Fault, but the available data suggest slip rates of 12 ±6 mm/yr for the
northern segments of the fault, and slip rates of 4 ±2 mm/yr for the southern
segments. For large ground-rupturing earthquakes on the San Jacinto fault, various
investigators have suggested a recurrence interval of 150 to 300 years. The Working
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Group on California Earthquake Probabilities (2008) has estimated that there is a 31
percent probability that an earthquake of M6.7 or greater will occur within 30 years
on this fault. Maximum credible earthquakes of M6.7, M6.9 and M7.2 are expected
on the San Bernardino, San Jacinto Valley and Anza segments, respectively, capable
of generating peak horizontal ground accelerations of 0.48g to 0.53g in the County
of Riverside. A M5.4 earthquake occurred on the San Jacinto Fault on July 7, 2010.
The United States Geological Survey has issued the following statements with respect
to the recent seismic activity on southern California faults:
The San Jacinto fault, along with the Elsinore, San Andreas, and other
faults, is part of the plate boundary that accommodates about 2
inches/year of motion as the Pacific plate moves northwest relative to
the North American plate. The largest recent earthquake on the San
Jacinto fault, near this location, the M6.5 1968 Borrego Mountain
earthquake April 8, 1968, occurred about 25 miles southeast of the July
7, 2010, M5.4 earthquake. This M5.4 earthquake follows the 4th of April
2010, Easter Sunday, M7.2 earthquake, located about 125 miles to the
south, well south of the US Mexico international border. A M4.9
earthquake occurred in the same area on June 12th at 8:08 pm (Pacific
Time). Thus, this section of the San Jacinto fault remains active.
Seismologists are watching two major earthquake faults in southern
California. The San Jacinto fault, the most active earthquake fault in
southern California, extends for more than 100 miles from the
international border into San Bernardino and Riverside, a major
metropolitan area often called the Inland Empire. The Elsinore fault is
more than 110 miles long, and extends into the Orange County and Los
Angeles area as the Whittier fault. The Elsinore fault is capable of a
major earthquake that would significantly affect the large metropolitan
areas of southern California. The Elsinore fault has not hosted a major
earthquake in more than 100 years. The occurrence of these
earthquakes along the San Jacinto fault and continued aftershocks
demonstrates that the earthquake activity in the region remains at an
elevated level. The San Jacinto fault is known as the most active
earthquake fault in southern California. Caltech and USGS seismologist
continue to monitor the ongoing earthquake activity using the
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Caltech/USGS Southern California Seismic Network and a GPS network
of more than 100 stations.
B. Other Geologic Hazards
Ground Rupture: Ground rupture is characterized by bedrock slippage along an
established fault and may result in displacement of the ground surface. For ground
rupture to occur along a fault, an earthquake usually exceeds M5.0. If a M5.0
earthquake were to take place on a local fault, an estimated surface-rupture length
1 mile long could be expected (Greensfelder, 1974). Our investigation indicates that
the subject site is not directly on a known active fault trace and, therefore, the risk
of ground rupture is remote.
Ground Shaking: Structural damage caused by seismically induced ground shaking
is a detrimental effect directly related to faulting and earthquake activity. Ground
shaking is considered to be the greatest seismic hazard in San Diego County. The
intensity of ground shaking is dependent on the magnitude of the earthquake, the
distance from the earthquake, and the seismic response characteristics of underlying
soils and geologic units. Earthquakes of M5.0 or greater are generally associated
with significant damage. It is our opinion that the most serious damage to the site
would be caused by a large earthquake originating on a nearby strand of the Rose
Canyon, Coronado Bank or Newport-Inglewood Faults. Although the chance of such
an event is remote, it could occur within the useful life of the structure.
Landslides: Our investigation indicates that the subject site is not directly on a known
recent or ancient landslide. Review of the “Geologic Map of the Oceanside 30’x60’
Quadrangle, California” by Kennedy and Tan (2007) and the USGS Landslide Hazard
Program Site (US Landslide Inventory), indicate that there are no known or suspected
ancient landslides located on the site.
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Slope Stability: Our site reconnaissance indicates that the site slopes gently in an
eastern direction, with only an 8-foot difference in elevation across the area of the
site. The site is underlain by relatively stable and dense Old Paralic Deposits, Unit 6-
7 formational materials at a depth of 1.0 to 3.0 feet. In our opinion, there is not a
slope stability issue with the site.
Liquefaction: The liquefaction of saturated sands during earthquakes can be a major
cause of damage to buildings. Liquefaction is the process by which soils are
transformed into a viscous fluid that will flow as a liquid when unconfined. It occurs
primarily in loose, cohesionless saturated silt, sand, and fine-grained gravel deposits
of Holocene to late Pleistocene age and in areas where the groundwater is shallower
than about 50 feet (DMG Special Publication 117) when they are sufficiently shaken
by an earthquake. On this site, the risk of liquefaction of formational materials due
to seismic shaking is considered to be very low due to the dense to very dense nature
of the underlying formational materials and the lack of shallow static groundwater.
The site does not have a potential for soil strength loss to occur due to a seismic
event.
Tsunamis and Seiches: A tsunami is a series of long waves generated in the ocean
by a sudden displacement of a large volume of water. Underwater earthquakes,
landslides, volcanic eruptions, meteor impacts, or onshore slope failures can cause
this displacement. Tsunami waves can travel at speeds averaging 450 to 600 miles
per hour. As a tsunami nears the coastline, its speed diminishes, its wave length
decreases, and its height increases greatly. After a major earthquake or other
tsunami-inducing activity occurs, a tsunami could reach the shore within a few
minutes. One coastal community may experience no damaging waves while another
may experience very destructive waves. Some low-lying areas could experience
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severe inland inundation of water and deposition of debris more than 3,000 feet
inland.
The site is located approximately 0.17-mile from the exposed coastline and at an
elevation of approximately 59 to 67 feet above MSL. Review of the Tsunami
Inundation Map for Emergency Planning, Encinitas Quadrangle, the site is located
outside the inundation area. There is no risk of tsunami inundation at the site.
A seiche is a run-up of water within a lake or embayment triggered by fault- or
landslide-induced ground displacement. The site is located near a coastal lagoon,
that is not considered capable of producing a seiche and inundating the subject site.
Flood Hazard: Review of the FEMA flood maps number 06073C0764H, effective on
12/20/2019, the project site is located within the Special Flood Hazard Area (SFHA)
X. Zone X is described as minimal flood hazard. The civil engineer should verify this
statement with the City of Carlsbad and County of San Diego (FEMA, 2019).
Geologic Hazards Summary: It is our opinion, based upon a review of the available
maps, our research and our site investigation, that the site is underlain at shallow
depth by stable Old Paralic Deposits formational materials and is suited for the
proposed residential structures. retaining walls and associated improvements
provided the recommendations herein are implemented. Furthermore, based on the
available information at this stage, it appears the proposed site development will not
destabilize or result in settlement of adjacent property or improvements if the
recommendations presented in this report are implemented.
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No significant geologic hazards are known to exist on the site that would prohibit the
construction of the proposed residential structures, retaining walls and associated
improvements. Ground shaking from earthquakes on active southern California faults
and active faults in northwestern Mexico is the greatest geologic hazard at the
property. Design of building structures in accordance with the current building codes
would reduce the potential for injury or loss of human life. Buildings constructed in
accordance with current building codes may suffer significant damage but should not
undergo total collapse.
In our explicit professional opinion, no active or potentially active faults underlie the
project site.
IX. GROUNDWATER
Free groundwater was not encountered in our exploratory excavations to the
maximum depths explored. A more detailed description of the subsurface materials
encountered in our exploratory excavations Figure Nos. IIIa-e.
It should also be recognized that minor groundwater seepage problems might occur
after development of a site even where none were present before development.
These are usually minor phenomena and are often the result of an alteration in
drainage patterns and/or an increase in irrigation water. Based on the permeability
characteristics of the soil and the anticipated usage and development, it is our opinion
that any seepage problems, which may occur, will be minor in extent. It is further
our opinion that these problems can be most effectively corrected on an individual
basis if and when they occur.
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We do not anticipate significant groundwater problems to develop in the future, if the
property is developed as proposed and proper drainage is implemented and
maintained.
It should be kept in mind that any required construction operations will change
surface drainage patterns and/or reduce permeabilities due to the densification of
compacted soils. Such changes of surface and subsurface hydrologic conditions, plus
irrigation of landscaping or significant increases in rainfall, may result in the
appearance of surface or near-surface water at locations where none existed
previously. The damage from such water is expected to be localized and cosmetic in
nature, if good positive drainage is implemented, as recommended in this report,
during and at the completion of construction.
On properties such as the subject site where dense, low permeability soils exist at
shallow depths, even normal landscape irrigation practices on the property or
neighboring properties, or periods of extended rainfall, can result in shallow
“perched” water conditions. The perching (shallow depth) accumulation of water on
a low permeability surface can result in areas of persistent wetting and drowning of
lawns, plants and trees. Resolution of such conditions, should they occur, may
require site-specific design and construction of subdrain and shallow “wick” drain
dewatering systems.
Subsurface drainage with a properly designed and constructed subdrain system will
be required along with continuous back drainage behind any proposed lower-level
basement walls, property line retaining walls, or any perimeter stem walls for raised-
wood floors where the outside grades are higher than the crawl space grades.
Furthermore, crawl spaces, if used, should be provided with the proper cross-
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ventilation to help reduce the potential for moisture-related problems. Additional
recommendations may be required at the time of construction.
It must be understood that unless discovered during site exploration or encountered
during site construction operations, it is extremely difficult to predict if or where
perched or true groundwater conditions may appear in the future. When site fill or
formational soils are fine-grained and of low permeability, water problems may not
become apparent for extended periods of time.
Water conditions, where suspected or encountered during construction, should be
evaluated and remedied by the project civil and geotechnical consultants. The project
developer and property owner, however, must realize that post-construction
appearances of groundwater may have to be dealt with on a site-specific basis.
Proper functional surface drainage should be implemented and maintained at the
property.
X. CONCLUSIONS & RECOMMENDATIONS
The following recommendations are based upon the practical field investigations
conducted by our firm, and resulting laboratory tests, in conjunction with our
knowledge and experience with similar soils in the Carlsbad area. The opinions,
conclusions, and recommendations presented in this report are contingent upon
Geotechnical Exploration, Inc. being retained to review the final plans and
specifications as they are developed and to observe the site earthwork and
installation of foundations. Accordingly, we recommend that the following paragraph
be included on the grading and foundation plans for the project.
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If the geotechnical consultant of record is changed for the project, the
work shall be stopped until the replacement has agreed in writing to
accept responsibility within their area of technical competence for
approval upon completion of the work. It shall be the responsibility of
the permittee to notify the governing agency in writing of such change
prior to the recommencement of grading and/or foundation installation
work and comply with the governing agency’s requirements for a change
to the Geotechnical Consultant of Record for the project.
We recommend that the planned residential structures, garages and retaining walls
be supported by conventional, individual-spread and/or continuous footing
foundations founded on medium dense to dense formational soils and minimum 90
percent compacted structural fill soils. Individual structures may bear on dense
formational or fill soils depending on their locations, final grading elevations and
exposure of formational materials.
Existing fill soils across the entire site will be disturbed during the demolition of the
existing structures, and are not suitable in their current condition to support new
structures or associated improvements. A full removal and recompaction of existing
fill and residual soils across the site will be required to support the proposed
structures and associated improvements. Fill soils across the site will be required to
be compacted to at least 90 percent relative compaction. Existing fill soil and
formational materials are suitable for use as recompacted fill soils. Any buried trash
and roots encountered during site demolition and fill soil recompaction should be
removed and exported off site.
It is our opinion that the site is suitable for the planned residential project provided
the recommendations herein are incorporated during design and construction.
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A. Preparation of Soils for Site Development
1. General: Grading should conform to the guidelines presented in the 2019
California Building Code (CBC), as well as the requirements of the City of
Carlsbad.
During earthwork construction, removals and reprocessing of fill materials, as
well as general grading procedures of the contractor should be observed and
the fill placed selectively tested by representatives of the geotechnical
engineer, Geotechnical Exploration Inc. If any unusual or unexpected
conditions are exposed in the field, they should be reviewed by the
geotechnical engineer and if warranted, modified and/or additional remedial
recommendations will be offered. Specific guidelines and comments pertinent
to the planned development are provided herein.
The recommendations presented herein have been completed using the
information provided to us regarding site development. If information
concerning the proposed development is revised, or any changes in the design
and location of the proposed property modified or approved in writing by this
office.
2. Clearing and Stripping: Complete demolition of the existing residential
structure and associated improvements should be undertaken. This is to
include the complete removal of all subsurface footings, utility lines and
miscellaneous debris. After clearing the entire ground surface of the site
should be stripped of existing vegetation within the areas of proposed new
construction. This includes any roots from existing trees and shrubbery. Holes
resulting from the removal of root systems or other buried obstructions that
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extend below the planned grades should be cleared and backfilled with suitable
compacted material compacted to the requirements provided under
Recommendation Nos. 3, 4 and 5 below. Prior to any filling operations, the
cleared and stripped vegetation and debris should be disposed of off-site.
3. Excavation: After the entire site has been cleared and stripped, all of the
existing fill soils and topsoil should be removed and recompacted. The depth
of removal across the site will vary depending on the thickness of unsuitable
soils overlying the formational materials. It is anticipated that the depth of
removal will be at least 3 feet below existing grade in the area of the existing
house pad, however, shallower removal (at least 2 feet) may be anticipated
across the remainder of the site. Based on the results of our exploratory
trenches and test holes, as well as our experience with similar materials in the
project area, it is our opinion that the existing fill soils and topsoil materials
can be excavated utilizing ordinary light to heavy weight earthmoving
equipment. Contractors should not, however, be relieved of making their own
independent evaluation of excavating the on-site materials prior to submitting
their bids. Contractors should also review this report along with the trench
logs to understand the scope and quantity of grading required for this project.
Variability in excavating the subsurface materials should be expected across
the project area.
The areal extent required to remove the surficial soils should be confirmed by
our representatives during the excavation work based on their examination of
the soils being exposed. The lateral extent of the excavation and recompaction
should be at least 5 feet beyond the edge of the perimeter ground level
foundations of the new residential structure and any areas to receive exterior
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improvements, or fill slopes, where feasible, or to the depth of excavation or
fill at that location, whichever is greater.
4. Cut-Fill Transition: Based on the review of the preliminary survey plans it
appears that the new residential structure may be planned to be constructed
on a cut-fill transition line.
New structures should not bear on a cut-fill transition line. If a cut-fill
transition line exists within the proposed building envelope, we recommend
that the cut portion of the building pad, be undercut to a minimum of 24 inches
below the bottom of the proposed footing depth. The bottom of the over
excavation should be observed and approved by a representative of
Geotechnical Exploration Inc., to verify that all loose and unsuitable soils
have been completely removed prior to reprocessing. After approval, the
bottom of the excavation should be scarified to a minimum depth of 8 inches
below removal grade elevations, brought to near-optimum moisture conditions
and recompacted to at least 90 percent relative compaction (based on ASTM
Test Method D1557). Backfill and compaction of the remaining structural fill
should be performed based on the recommendations presented in the following
sections. No structures should be supported on a building pad with structural
fill soil thickness differential of greater than 5 feet.
5. Subgrade Preparation: After the site has been cleared, stripped, and the
required excavations made, the exposed subgrade soils in areas to receive new
fill and/or slab on-grade building improvements should be scarified to a depth
of 6 inches, moisture conditioned, and compacted to the requirements for
structural fill. While not anticipated, in the event that planned cuts expose any
medium to highly expansive formational materials in the building areas, they
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should be scarified and moisture conditioned to at least 3 percent over
optimum moisture for low expansive soils and 5 percent for medium and highly
expansive soils (if encountered).
6. Material for Fill: Existing on-site low-expansion potential (Expansion Index of
50 or less per ASTM D4829-19) soils with an organic content of less than 3
percent by volume are, in general, suitable for use as fill. Imported fill
material, where required, should have a low-expansion potential. In addition,
both imported and existing on-site materials for use as fill should not contain
rocks or lumps more than 6 inches in greatest dimension if the fill soils are
compacted with heavy compaction equipment (or 3 inches in greatest
dimension if compacted with lightweight equipment). All materials for use as
fill should be approved by our representative prior to importing to the site.
If encountered at the site, medium to highly expansive soils should not be used
as structural fill at a depth of less than 5 feet from footing bearing surface
elevation or behind retaining walls. Backfill material placed behind retaining
walls should be low expansive (E.I. less than 50), with rocks no larger than 3
inches in diameter.
7. Structural Fill Compaction: All structural fill, and areas to receive any
associated improvements, should be compacted to a minimum degree of
compaction of 90 percent based upon ASTM D1557-12e1. Fill material should
be spread and compacted in uniform horizontal lifts not exceeding 8 inches in
uncompacted thickness. Before compaction begins, the fill should be brought
to a water content that will permit proper compaction by either: (1) aerating
and drying the fill if it is too wet, or (2) watering the fill if it is too dry. Each
lift should be thoroughly mixed before compaction to ensure a uniform
distribution of moisture. For low expansive soils, the moisture content should
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be within 2 percent of optimum. Although we do not anticipate any medium
to high expansive soils to be exposed during grading operations, if
encountered, the compaction moisture content should be at least 5 percent
over optimum.
Any rigid improvements founded on the existing undocumented fill soils can
be expected to undergo movement and possible damage. Geotechnical
Exploration, Inc. takes no responsibility for the performance of any
improvements built on loose natural soils or inadequately compacted fills.
Subgrade soils in any exterior area receiving concrete improvements should
be verified for compaction and moisture by a representative of our firm within
48 hours prior to concrete placement.
No uncontrolled fill soils should remain after completion of the site work. In
the event that temporary ramps or pads are constructed of uncontrolled fill
soils, the loose fill soils should be removed and/or recompacted prior to
completion of the grading operation. Based on the results of our laboratory
testing, the water-soluble sulfate content of the tested soils at the site yielded
a negligible sulfate exposure, as such based on table 1904.3 of the building
code, there is no restrictions for cement type.
8. Trench and Retaining Wall Backfill: All utility trenches and retaining walls
should be backfilled with properly compacted fill. Backfill material should be
placed in lift thicknesses appropriate to the type of compaction equipment
utilized and compacted to a minimum degree of compaction of 90 percent
based upon ASTM D1557-12e1 by mechanical means. Any portion of the
trench backfill in public street areas within pavement sections should conform
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to the material and compaction requirements of the adjacent pavement
section.
Backfill soils placed behind retaining walls should be installed as early as the
retaining walls are capable of supporting lateral loads. Backfill soils behind
retaining walls should be low expansive (Expansion Index less than 50 per
ASTM D4829-19).
Our experience has shown that even shallow, narrow trenches (such as for
irrigation and electrical lines) that are not properly compacted can result in
problems, particularly with respect to shallow groundwater accumulation and
migration.
9. Observations and Testing: During grading, our firm should observe and test
the grading soils as stated in CBC 2019, Section 1705.6 Soils: “Special
inspections and tests of existing site soil conditions, fill placement and load-
bearing requirements shall be performed in accordance with this section and
Table 1705.6 (see below). The approved geotechnical report and the
construction documents prepared by the registered design professionals shall
be used to determine compliance. During fill placement, the special inspector
shall verify that proper materials and procedures are used in accordance with
the provisions of the approved geotechnical report”.
A summary of Table 1705.6 “REQUIRED SPECIAL INSPECTIONS AND TESTS
OF SOILS” is presented below:
a) Verify materials below shallow foundations are adequate to achieve the
design bearing capacity;
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b)Verify excavations are extended to proper depth and have reached
proper material;
c)Perform classification and testing of compacted fill materials;
d)Verify use of proper materials, densities and thicknesses during
placement and compaction of compacted fill prior to placement of compacted
fill, inspect subgrade and verify that site has been prepared properly
Section 1705.6 “Soils” statement and Table 1705.6 indicate that it is
mandatory that a representative of this firm (responsible engineering firm),
perform observations and fill compaction testing during excavation operations
to verify that the remedial operations are consistent with the recommendations
presented in this report. All grading excavations resulting from the removal
of soils should be observed and evaluated by a representative of our firm
before they are backfilled.
Our firm should observe the bearing soils of the excavation bottoms (including
the bottom of the building pad undercut) and footing trench excavations of the
main structure and exterior structures such as retaining/site walls, and collect
soils samples to obtain and verify the maximum dry density of the on-site or
imported soils to be used as backfill material for the grading or retaining wall
backfill. Our firm should also perform field density tests of compacted soils
placed at least every 2 feet in thickness, verify the adequacy of the soil
moisture content and relative compaction.
In addition, our firm should verify the adequacy of imported soils by performing
sieve and expansion index tests, as well as maximum dry density tests and
optimum moisture tests; verify the compaction and moisture content of
subgrade soils to receive pavement or flatwork improvements; obtain soil
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samples and perform R-values for public street areas (if required to verify the
adequacy of pavement cross sections; and verify the compaction of the asphalt
concrete and the adequacy of the grain size for the base material.
B. Seismic Design Criteria
10. Seismic Data Bases: The estimation of the peak ground acceleration and the
repeatable high ground acceleration (RHGA) likely to occur at the site is based
on the known significant local and regional faults within 100 miles of the site.
11. Seismic Design Criteria: The proposed structure should be designed in
accordance with the 2019 CBC, which incorporates by reference the ASCE 7-
16 for seismic design. We have determined the mapped spectral acceleration
values for the site based on a latitude of 33.1470 degrees and a longitude
of -117.3425 degrees, utilizing a program titled “Seismic Design Map Tool” and
provided by the USGS through SEAOC, which provides a solution for ASCE 7-
16 utilizing digitized files for the Spectral Acceleration maps. See Appendix B.
12. Structure and Foundation Design: The design of the new structures and
foundations should be based on Seismic Design Category D, Risk Category II
for a Site Class C-Very Dense Soil and Soft Rock.
13. Spectral Acceleration and Design Values: The structural seismic design, when
applicable, should be based on the following values, which are based on the
site location, soil characteristics, and seismic maps by USGS, as required by
the 2019 CBC. The summarized seismic soil parameters are presented in Table
I below, have been calculated with the SEAOC Seismic Design Map Tool. The
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complete values are included in Appendix B. The Site Class C values for this
property are:
TABLE I
Mapped Spectral Acceleration Values and Design Parameters
SS S1 SMS SM1 SDS SD1 Fa Fv PGA PGAM SDC
1.098 0.396 1.317 0.594 0.878 0.396 1.2 1.5 0.486 0.583 D
C. Foundation Recommendations
14. Footings: We recommend that the proposed structures be supported on
conventional, individual-spread and/or continuous footing foundations bearing
on undisturbed formational materials or on properly compacted fill soils over
formational soils. No footings should be underlain by undocumented fill soils.
All building footings should be built on formational soils or properly compacted
fill prepared as recommended above in Recommendation Nos. 3, 4 and 5. The
footings should be founded at least 18 inches below the lowest adjacent
finished grade when founded into properly compacted fill or formational soils.
Footings located adjacent to utility trenches should have their bearing surfaces
situated below an imaginary 1.0:1.0 plane projected upward from the bottom
edge of the adjacent utility trench. Otherwise, the utility trenches should be
excavated farther from the footing locations.
Footings located adjacent to the tops of slopes should be extended sufficiently
deep so as to provide at least 8 feet of horizontal cover between the slope face
and outside edge of the footing at the footing bearing level.
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15. Bearing Values: At the recommended depths, footings on formational or
properly compacted fill soils may be designed for allowable bearing pressures
of 2,500 psf for combined dead and live loads and 3,325 psf for all loads,
including wind or seismic. The footings should, however, have a minimum
width of 15 inches. An increase in soil allowable static bearing can be used as
follows: 800 psf for each additional foot over 1.5 feet in depth and 400 psf for
each additional foot in width to a total not exceeding 4,000 psf. The static soil
bearing value may be increased one-third for seismic and wind load analysis.
As previously indicated, all of the foundations for the building should be built
on dense formational soils or properly compacted fill soils.
16. Footing Reinforcement: All continuous footings should contain top and bottom
reinforcement to provide structural continuity and to permit spanning of local
irregularities. We recommend that a minimum of two No. 5 top and two No.
5 bottom reinforcing bars be provided in the footings. All footings should be
reinforced as specified by the structural engineer. A minimum clearance of 3
inches should be maintained between steel reinforcement and the bottom or
sides of the footing. Isolated square footings should contain, as a minimum,
a grid of three No. 4 steel bars on 12-inch centers, both ways. In order for us
to offer an opinion as to whether the footings are founded on soils of sufficient
load bearing capacity, it is essential that our representative inspect the footing
excavations prior to the placement of reinforcing steel or forms.
NOTE: The project Civil/Structural Engineer should review all reinforcing
schedules. The reinforcing minimums recommended herein are not to be
construed as structural designs, but merely as minimum reinforcement to
reduce the potential for cracking and separations.
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17. Lateral Loads: Lateral load resistance for the structure supported on footing
foundations may be developed in friction between the foundation bottoms and
the supporting subgrade. An allowable friction coefficient of 0.35 is considered
applicable. An additional allowable passive resistance equal to an equivalent
fluid weight of 275 pounds per cubic foot (pcf) acting against the foundations
may be used in design provided the footings are poured neat against the dense
formational or properly compacted fill materials. These lateral resistance value
assume a level surface in front of the footing for a minimum distance of three
times the embedment depth of the footing and any shear keys, but not less
than 8 feet from a slope face, measured from effective top of foundation.
Retaining walls supporting surcharge loads or affected by upper foundations
should consider the effect of those upper loads.
18. Settlement: Settlements under structural design loads are expected to be
within tolerable limits for the proposed structures. For footings designed in
accordance with the recommendations presented in the preceding paragraphs,
we anticipate that the total and differential static settlement for the proposed
improvements will be on the order of 1 inch and approximately, post-
construction differential settlement angular rotation should be less than 1/240.
D. Concrete Slab On-Grade Criteria
Slabs on-grade may only be used on new, properly compacted fill or when bearing
on dense formational soils.
19. Minimum Floor Slab Thickness and Reinforcement: Based on our experience,
we have found that, for various reasons, floor slabs occasionally crack.
Therefore, we recommend that all slabs on-grade contain at least a minimum
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amount of reinforcing steel to reduce the separation of cracks, should they
occur. Slab subgrade soil should be verified by a Geotechnical Exploration,
Inc. representative to have the proper moisture content within 48 hours prior
to placement of the vapor barrier and pouring of concrete.
New interior floor slabs should be a minimum of 4-inches actual thickness and
be reinforced with No. 4 bars on 18-inch centers, both ways, placed at mid-
height in the slab. Soil moisture content should be kept above the optimum
prior to waterproofing placement under the new concrete slab. Shrinkage
joints should be specified by the structural engineer.
We note that shrinkage cracking can result in reflective cracking in brittle
flooring surfaces such as stone and tiles. It is imperative that if movement
intolerant flooring materials are to be utilized, the flooring contractor and/or
architect should provide specifications for the use of high-quality isolation
membrane products installed between slab and floor materials.
20. Slab Moisture Emission: Although it is not the responsibility of geotechnical
engineering firms to provide moisture protection recommendations, as a
service to our clients we provide the following discussion and suggested
minimum protection criteria. Actual recommendations should be provided by
the project architect and waterproofing consultants or product manufacturer.
It is recommended to contact the vapor barrier manufacturer to schedule a
pre-construction meeting and to coordinate a review, in-person or digital, of
the vapor barrier installation.
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Carlsbad, California Page 40
Soil moisture vapor can result in damage to moisture-sensitive floors, some
floor sealers, or sensitive equipment in direct contact with the floor, in addition
to mold and staining on slabs, walls and carpets. The common practice in
Southern California is to place vapor retarders made of PVC, or of polyethylene.
PVC retarders are made in thickness ranging from 10- to 60-mil. Polyethylene
retarders, called visqueen, range from 5- to 10-mil in thickness. These
products are no longer considered adequate for moisture protection and can
actually deteriorate over time.
Specialty vapor retarding and barrier products possess higher tensile strength
and are more specifically designed for and intended to retard moisture
transmission into and through concrete slabs. The use of such products is
highly recommended for reduction of floor slab moisture emission.
The following American Society for Testing and Materials (ASTM) and American
Concrete Institute (ACI) sections address the issue of moisture transmission
into and through concrete slabs: ASTM E1745-17 Standard Specification for
Plastic Water Vapor Retarders Used in Contact Concrete Slabs; ASTM E1643-
18a Standard Practice for Selection, Design, Installation, and Inspection of
Water Vapor Retarders Used in Contact with Earth or Granular Fill Under
Concrete Slabs; ACI 302.2R-06 Guide for Concrete Slabs that Receive
Moisture-Sensitive Flooring Materials; and ACI 302.1R-15 Guide to Concrete
Floor and Slab Construction.
20.1 Based on the above, we recommend that the vapor barrier consist of a
minimum 15-mil extruded polyolefin plastic (no recycled content or
woven materials permitted). Permeance as tested before and after
mandatory conditioning (ASTM E1745 Section 7.1 and subparagraphs
Garfield Street Homes Job No. 20-12942
Carlsbad, California Page 41
7.1.1-7.1.5) should be less than 0.01 perms (grains/square
foot/hour/per inch of Mercury) and comply with the ASTM E1745-17
Class A requirements. Installation of vapor barriers should be in
accordance with ASTM E1643-18a. The basis of design is 15-mil Stego
Wrap vapor barrier placed per the manufacturer’s guidelines. Reef
Industries Vapor Guard membrane has also been shown to achieve a
permeance of less than 0.01 perms. We recommend that the slab be
poured directly on the vapor barrier, which is placed directly on the
prepared properly compacted smooth subgrade soil surface.
20.2 Common to all acceptable products, vapor retarder/barrier joints must
be lapped at least 6 inches. Seam joints and permanent utility
penetrations should be sealed with the manufacturer’s recommended
tape or mastic. Edges of the vapor retarder should be extended to
terminate at a location in accordance with ASTM E1643-18a or to an
alternate location that is acceptable to the project’s structural engineer.
All terminated edges of the vapor retarder should be sealed to the
building foundation (grade beam, wall, or slab) using the manufacturer’s
recommended accessory for sealing the vapor retarder to pre-existing
or freshly placed concrete. Additionally, in actual practice, stakes are
often driven through the retarder material, equipment is dragged or
rolled across the retarder, overlapping or jointing is not properly
implemented, etc. All these construction deficiencies reduce the
retarder’s effectiveness. In no case should retarder/barrier products be
punctured or gaps be allowed to form prior to or during concrete
placement. Vapor barrier-safe screeding and forming systems should
be used that will not leave puncture holes in the vapor barrier, such as
Beast Foot (by Stego Industries) or equivalent.
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20.3 Vapor retarders/barriers do not provide full waterproofing for structures
constructed below free water surfaces. They are intended to help reduce
or prevent vapor transmission and/or capillary migration through the
soil and through the concrete slabs. Waterproofing systems must be
designed and properly constructed if full waterproofing is desired. The
owner and project designers should be consulted to determine the
specific level of protection required.
20.4 Following placement of any concrete floor slabs, sufficient drying time
must be allowed prior to placement of floor coverings. Premature
placement of floor coverings may result in degradation of adhesive
materials and loosening of the finish floor materials.
21. Exterior Slab Thickness and Reinforcement: As a minimum for protection of
on-site improvements, we recommend that all exterior pedestrian concrete
slabs be 4 inches thick and be founded on properly compacted and tested fill,
with No. 3 bars at 15-inch centers, both ways, at the center of the slab, and
contain adequate isolation and control joints. The performance of on-site
improvements can be greatly affected by soil base preparation and the quality
of construction. It is therefore important that all improvements are properly
designed and constructed for the existing soil conditions. The improvements
should not be built on loose soils or fills placed without our observation and
testing.
For exterior slabs with the minimum shrinkage reinforcement, control joints
should be placed at spaces no farther than 15 feet apart or the width of the
slab, whichever is less, and also at re-entrant corners. Control joints in
Garfield Street Homes Job No. 20-12942
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exterior slabs should be sealed with elastomeric joint sealant. The sealant
should be inspected every 6 months and be properly maintained
E. Retaining Wall Design Criteria
22. Design Parameters – Unrestrained: The active earth pressure to be utilized in
the design of any cantilever site retaining walls, utilizing on-site low- expansive
[EI less than 50] or imported very low- to low-expansive soils [EI less than
50] as backfill should be based on an Equivalent Fluid Weight of 38 pcf (for
level backfill only). For 2.0:1.0 sloping backfill, the cantilever site retaining
walls should be designed with an equivalent fluid pressure of 52 pcf.
Unrestrained retaining walls should be backfilled with properly compacted very
low to low expansive soils. Unrestrained building retaining walls should be
designed for 38 pcf for level low expansive soil backfill, and use a conversion
load factor of 0.31 for vertical surcharge loads to be converted to uniform
lateral surcharge loads. Temporary cantilever shoring walls may use 45 pcf
active pressure, and a conversion factor of 0.36 to convert vertical uniform
surcharge to horizontal uniform pressure. For passive resistance, use the
value of 685 pcf times the diameter of the soldier pile, times the depth of
embedment below the grade excavation in front of the piles.
23. Design Parameters – Restrained: Temporary or permanent site restrained
shoring walls or restrained building retaining walls supporting low expansive
level backfill may utilize a triangular pressure increasing at a rate of 56 pcf for
wall design (78 pcf for sloping 2.0:1.0 backfill). The soil pressure produced by
any footings, improvements, or any other surcharge placed within a horizontal
distance equal to the height of the retaining portion of the wall should be
included in the wall design pressure. A conversion factor of 0.47 pcf may be
Garfield Street Homes Job No. 20-12942
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used to convert vertical uniform surcharge loads to lateral uniform pressure
behind a restrained retaining wall with level backfill and 0.64 when supporting
a 2 to 1 sloping backfill. The recommended lateral soil pressures are based on
the assumption that no loose soils or unstable soil wedges will be retained by
the retaining wall. Backfill soils should consist of low-expansive soils with EI
less than 50, and should be placed from the heel of the foundation to the
ground surface within the wedge formed by a plane at 30 from vertical, and
passing by the heel of the foundation and the back face of the retaining wall.
24. Retaining Wall Seismic Design Pressures: For seismic design of unrestrained
walls over 6 feet in exposed height, we recommend that the seismic pressure
increment be taken as a fluid pressure distribution utilizing an equivalent fluid
weight of 16 pcf. This seismic increment is waived for restrained basement
walls. If the walls are designed as unrestrained walls, then the seismic load
should be added to the static soil pressure.
25. Basement/Retaining Wall Drainage: The preceding design pressures assume
that the walls are backfilled with properly compacted low expansion potential
materials (Expansion Index less than 50) and that there is sufficient drainage
behind the walls to prevent the build-up of hydrostatic pressures from surface
water infiltration. We recommend that drainage be provided by a composite
drainage material such as J-Drain 200/220 and J-Drain SWD, or equivalent.
No perforated pipes or gravel are utilized with the J-Drain system. The drain
material should terminate 12 inches below the exterior finish surface where
the surface is covered by slabs or 18 inches below the finish surface in
landscape areas (see Figure No. VI for Schematic Retaining Wall Subdrain
Recommendations). Waterproofing should extend from the bottom to the top
of the wall.
Garfield Street Homes Job No. 20-12942
Carlsbad, California Page 45
Backfill placed behind retaining walls should be compacted to a minimum
degree of compaction of 90 percent using light compaction equipment. If
heavy equipment is used, the walls should be appropriately temporarily
braced. Crushed rock gravel may only be used as backfill in areas where
access is too narrow to place compacted soils. Behind shoring walls sand slurry
backfill may be used behind lagging.
Geotechnical Exploration, Inc. will assume no liability for damage to
structures or improvements that is attributable to poor drainage. The
architectural plans should clearly indicate that subdrains for any lower-level
walls be placed at an elevation at least 1 foot below the bottom of the lower-
level slabs.
F. Slopes
26. Temporary Slopes: Based on our subsurface investigation work, laboratory
test results, and engineering analysis, temporary cut slopes up to 12 feet in
height in the formational materials should be stable from mass instability at
an inclination 0.75 :1.0 (horizontal to vertical). Temporary cut slopes up to
12 feet in height in loose fill soils should be stable against mass instability at
an inclination of 1.5:1.0. In properly compacted fill soils, temporary slopes
should be stable at a slope ratio of 1.0 to 1.0.
Some localized sloughing or raveling of the soils exposed on the slopes may
occur. Since the stability of temporary construction slopes will depend largely
on the contractor's activities and safety precautions (storage and equipment
loadings near the tops of cut slopes, surface drainage provisions, etc.), it
should be the contractor's responsibility to establish and maintain all
Garfield Street Homes Job No. 20-12942
Carlsbad, California Page 46
temporary construction slopes at a safe inclination appropriate to the methods
of operation. No soil stockpiles or surcharge may be placed within a horizontal
distance of 10 feet or the depth of the excavation, whichever is larger, from
the excavation top.
If these recommendations are not feasible due to space constraints, temporary
shoring may be required for safety and to protect adjacent property
improvements. Similarly, footings near temporary cuts should be underpinned
or protected with shoring.
26.1 Temporary Excavations: Temporary vertical excavation slots should be
executed in an “A-B-C” alternating slot method close to property lines. Slots
should not be taller than 3½ feet for new property line retaining walls. The
total slot width of the recommended slots should be no longer than 8 feet.
Other interior excavations deeper than 3 feet can be made at a 1.0:1.0 slope
ratio. Temporary excavations are anticipated at proposed retaining wall
locations shown on the grading plan.
27. Slope Observations: A representative of Geotechnical Exploration, Inc.
must observe any steep temporary slopes during construction. In the event
that soils and formational material comprising a slope are not as anticipated,
any required slope design changes would be presented at that time.
28. Permanent Slopes: Any new or existing cut or fill slopes up to 10 feet in height
should be constructed at an inclination of 2.0:1.0 (horizontal to vertical), be
provided with a keyway at least 2 feet in depth and at least 8 feet in width for
the entire length of the slope. Permanent slopes at a 2.0:1.0 slope ratio should
possess a factor of safety of 1.5 against deep and shallow failure.
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G. Pavements
29. Concrete Pavement: We recommend that driveways subject only to
automobile and light truck traffic be 5.5 inches thick and be supported directly
on properly prepared/compacted on-site subgrade soils. The upper 6 inches
of the subgrade below the slab should be compacted to a minimum degree of
compaction of 95 percent just prior to paving. The concrete should conform
to Section 201 of The Standard Specifications for Public Works Construction,
2021 Edition, for Class 560-C-3250.
In order to control shrinkage cracking, we recommend that saw-cut,
weakened-plane joints be provided at about 12-foot centers both ways and at
reentrant corners. The pavement slabs should be saw-cut as soon as practical
but no more than 24 hours after the placement of the concrete. The depth of
the joint should be one-quarter of the slab thickness and its width should not
exceed 0.02-foot. Reinforcing steel is not necessary unless it is desired to
increase the joint spacing recommended above.
30. Interlocking Permeable Pavers: If desired, we recommend that permeable
pavement pavers for the driveway, subject only to automobile and light truck
traffic, be supported on a 1.5 inches of bedding sand No. 8 on either 6 inches
of Crushed Miscellaneous Base conforming to Section 200-2 of the Standard
Specifications for Public Works Construction (2021 Edition) or 6 inches of No.
57 crushed rock gravel per ASTM D448 gradation. The upper 6 inches of the
pavement subgrade soil as well as the aggregate base layer should be
compacted to a minimum degree of compaction of 95 percent. Preparation of
the subgrade and placement of the base materials should be performed under
the observation of our representative.
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H. Site Drainage Considerations
31. Erosion Control: Appropriate erosion control measures should be taken at all
times during and after construction to prevent surface runoff waters from
entering footing excavations or ponding on finished building pad areas.
32. Surface Drainage: Adequate measures should be taken to properly finish-
grade the lot after the structures and other improvements are in place.
Drainage waters from this site and adjacent properties should be directed away
from the footings, floor slabs, and slopes, onto the natural drainage direction
for this area or into properly designed and approved drainage facilities
provided by the project civil engineer. Roof gutters and downspouts should be
installed on the residence, with the runoff directed away from the foundations
via closed drainage lines. Proper subsurface and surface drainage will help
minimize the potential for waters to seek the level of the bearing soils under
the footings and floor slabs.
Failure to observe this recommendation could result in undermining and
possible differential settlement of the structure or other improvements on the
site or cause other moisture-related problems. Currently, the CBC requires a
minimum 1 percent surface gradient for proper drainage of building pads
unless waived by the building official. Concrete pavement may have a
minimum gradient of 0.5-percent.
33. Planter Drainage: Planter areas, flower beds and planter boxes should be
sloped to drain away from the footings and floor slabs at a gradient of at least
5 percent within 5 feet from the perimeter walls. Any planter areas adjacent
to the residence or surrounded by concrete improvements should be provided
Garfield Street Homes Job No. 20-12942
Carlsbad, California Page 49
with sufficient area drains to help with rapid runoff disposal. No water should
be allowed to pond adjacent to the residence or other improvements or
anywhere on the site.
34. Drainage Quality Control: It must be understood that it is not within the scope
of our services to provide quality control oversight for surface or subsurface
drainage construction or retaining wall sealing and base of wall drain
construction. It is the responsibility of the contractor to verify proper wall
sealing, geofabric installation, protection board (if needed), drain depth below
interior floor or yard surface, pipe percent slope to the outlet, etc.
I. General Recommendations
35. Project Start Up Notification: In order to reduce work delays during site
development, this firm should be contacted 48 hours prior to any need for
observation of footing excavations or field density testing of compacted fill
soils. If possible, placement of formwork and steel reinforcement in footing
excavations should not occur prior to observing the excavations; in the event
that our observations reveal the need for deepening or re-designing foundation
structures at any locations, any formwork or steel reinforcement in the affected
footing excavation areas would have to be removed prior to correction of the
observed problem (i.e., deepening the footing excavation, recompacting soil
in the bottom of the excavation, etc.).
36. Cal-OSHA: Where not superseded by specific recommendations presented in
this report, trenches, excavations, and temporary slopes at the subject site
should be constructed in accordance with Title 8, Construction Safety Orders,
issued by Cal-OSHA.
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Carlsbad, California Page 50
37. Construction Best Management Practices (BMPs): Construction BMPs must be
implemented in accordance with the requirements of the controlling
jurisdiction. Sufficient BMPs must be installed to prevent silt, mud or other
construction debris from being tracked into the adjacent street(s) or storm
water conveyance systems due to construction vehicles or any other
construction activity. The contractor is responsible for cleaning any such
debris that may be in the street at the end of each work day or after a storm
event that causes breach in the installed construction BMPs.
All stockpiles of uncompacted soil and/or building materials that are intended
to be left unprotected for a period greater than 7 days are to be provided with
erosion and sediment controls. Such soil must be protected each day when
the probability of rain is 40% or greater. A concrete washout should be
provided on all projects that propose the construction of any concrete
improvements that are to be poured in place. All erosion/sediment control
devices should be maintained in working order at all times. All slopes that are
created or disturbed by construction activity must be protected against erosion
and sediment transport at all times. The storage of all construction materials
and equipment must be protected against any potential release of pollutants
into the environment.
XI. GRADING NOTES
Geotechnical Exploration, Inc. recommends that we be retained to verify the
actual soil conditions revealed during site grading work and footing excavation to be
as anticipated in this "Updated Report of Preliminary Geotechnical Investigation" for
the project. In addition, the placement and compaction of any fill or backfill soils
during site grading work must be observed and tested by the soil engineer.
Garfield Street Homes Job No. 20-12942
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It is the responsibility of the grading contractor and general contractor to comply with
the requirements on the grading plans as well as the local grading ordinance. All
retaining wall and trench backfill should be properly compacted. Geotechnical
Exploration, Inc. will assume no liability for damage occurring due to improperly or
uncompacted backfill placed without our observations and testing.
XII. LIMITATIONS
Our conclusions and recommendations have been based on available data obtained
from our field investigation and laboratory analysis, as well as our experience with
similar soils and formational materials located in this area of Carlsbad. Of necessity,
we must assume a certain degree of continuity between exploratory excavations
and/or natural exposures. It is, therefore, necessary that all observations,
conclusions, and recommendations be verified at the time grading operations begin
or when footing excavations are placed. In the event discrepancies are noted,
additional recommendations may be issued, if required.
The work performed and recommendations presented herein are the result of an
investigation and analysis that meet the contemporary standard of care in our
profession within the County of San Diego. No warranty is provided.
As stated previously, it is not within the scope of our services to provide quality
control oversight for surface or subsurface drainage construction or retaining wall
sealing and base of wall drain construction. It is the responsibility of the contractor
to verify proper wall sealing, geofabric installation, protection board installation (if
needed), drain depth below interior floor or yard surfaces; pipe percent slope to the
outlet, etc.
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Carlsbad, California Page 52
This report should be considered valid for a period of two (2) years, and is subject to
review by our firm following that time. If significant modifications are made to the
building plans, especially with respect to the height and location of any proposed
structures, this report must be presented to us for immediate review and possible
revision.
It is the responsibility of the owner and/or developer to ensure that the
recommendations summarized in this report are carried out in the field operations
and that our recommendations for design of this project are incorporated in the
project plans. We should be retained to review the project plans once they are
available, to verify that our recommendations are adequately incorporated in the
plans. Additional or modified recommendations may be issued if warranted after plan
review.
This firm does not practice or consult in the field of safety engineering. We do not
direct the contractor's operations, and we cannot be responsible for the safety of
personnel other than our own on the site; the safety of others is the responsibility of
the contractor. The contractor should notify the owner if any of the recommended
actions presented herein are considered to be unsafe.
The firm of Geotechnical Exploration, Inc. shall not be held responsible for
changes to the physical condition of the property, such as addition of fill soils or
changing drainage patterns, which occur subsequent to issuance of this report and
the changes are made without our observations, testing, and approval.
Garfield Street Homes Job No. 20-12942
Carlsbad, California Page 53
Once again, should any questions arise concerning this report, please feel free to
contact the undersigned. Reference to our Job No. 20-12942 will expedite a reply
to your inquiries.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
_______________________________ ______________________________
Jaime A. Cerros, P.E. Hector G. Estrella
R.C.E. 34422/G.E. 2007 P.G. 9019/C.E.G. 2656
Senior Geotechnical Engineer
________________________________
Cathy K. Ganze, Project Geologist
REFERENCES
JOB NO. 20-12942
December 2021
2007 Working Group on California Earthquake Probabilities, 2008, The Uniform California Earthquake
Rupture Forecast, Version 2 (UCERF 2), U.S Geological Survey Open-file Report 2007-1437 and
California Geological Survey Special Report 203.
Association of Engineering Geologists, 1973, Geology and Earthquake Hazards, Planners Guide to the
Seismic Safety Element, Association of Engineering Geologists, Southern California Section.
Berger, V. and Schug, D.L., 1991, Probabilistic Evaluation of Seismic Hazard in the San Diego-Tijuana
Metropolitan Region, Environmental Perils, San Diego Region, Geological Society of America by the San
Diego Association of Geologists, October 20, 1991, p. 89-99.
Crowell, J.C., 1962, Displacement Along the San Andreas, Fault, California, Geological Society of
America, Special Papers, no. 71.
Demere, T.A. 1997, Geology of San Diego County, California, San Diego Natural History Museum,
http://archive.sdnhm.org/research/paleontology/sdgeol.html, accessed July 30, 2020.
Grant Ludwig, L.B. and Shearer, P.M., 2004, Activity of the Offshore Newport-Inglewood Rose Canyon
Fault Zone, Coastal Southern California, from Relocated Microseismicity. Bulletin of the Seismological
Society of America, 94(2), 747-752.
Greene, H.G., Bailey, K.A., Clarke, S.H., Ziony, J.I. and Kennedy, M.P., 1979, Implications of fault patterns of the inner California continental borderland between San Pedro and San Diego, in Abbott, P.L., and Elliot, W.J., eds., Earthquakes and other perils, San Diego region: San Diego Association of
Geologists, Geological Society of America field trip, p. 21–28.
Greensfelder, R.W., 1974, Maximum Credible Rock Accelerations from Earthquakes in California,
California Division of Mines and Geology.
Hart E.W. and Bryant, W.A., 1997, Fault-Rupture Hazard Zones in California, California Division of Mines
and Geology, Special Publication 42.
Hart, E.W., Smith, D.P. and Saul, R.B., 1979, Summary Report: Fault Evaluation Program, 1978 Area
(Peninsular Ranges-Salton Trough Region), California Division of Mines and Geology, Open-file Report
79-10 SF, 10.
Hauksson, E. and Jones, L.M., 1988, The July 1986 Oceanside (ML=5.3) Earthquake Sequence in the
Continental Borderland, Southern California Bulletin of the Seismological Society of America, v. 78, p. 1885-1906. Hileman, J.A., Allen, C.R. and Nordquist, J.M., 1973, Seismicity of the Southern California Region,
January 1, 1932 to December 31, 1972, Seismological Laboratory, Cal-Tech, Pasadena, California.
Kennedy, M.P. and Tan, S.S., 2007, Geologic Map of the Oceanside 30’x60’ Quadrangle, California,
California Geological Survey, Department of Conservation.
Richter, C.F., 1958, Elementary Seismology, W.H. Freeman and Company, San Francisco, California.
REFERENCES/Page 2
Rockwell, T.K., 2010, The Rose Canyon Fault Zone in San Diego, Proceedings of the Fifth International
Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, Paper No.
7.06C.
Rockwell, T.K., Dawson, T.E., Young Ben-Horin, J. and Seitz, G., 2014, A 21-Event, 4,000-Year History
of Surface Ruptures in the Anza Seismic Gap, San Jacinto Fault, and Implications for Long-term
Earthquake Production on a Major Plate Boundary Fault, Pure and Applied Geophysics, v. 172, 1143–
1165.
Rockwell, T.K., Millman, D.E., McElwain, R.S. and Lamar, D.L., 1985, Study of Seismic Activity by
Trenching Along the Glen Ivy North Fault, Elsinore Fault Zone, Southern California: Lamar-Merifield
Technical Report 85-1, U.S.G.S. Contract 14-08-0001-21376, 19 p.
Ross, Z.E., Hauksson E. and Ben-Zion Y., 2017, Abundant Off-fault Seismicity and Orthogonal Structures
in the San Jacinto Fault Zone, Science Advances, 2017; 3(3): e1601946.
Toppozada, T.R. and Parke, D.L., 1982, Areas Damaged by California Earthquakes, 1900-1949,
California Division of Mines and Geology, Open-file Report 82-17.
U.S. Dept. of Agriculture, 1953, Aerial Photographs AXN-14M-19 and 20.
VICINITY MAP
Garfield Street Condominiums
4008 Garfield Street
Carlsbad, CA.Figure No. I
Job No. 20-12942
SITE
Thomas Guide San Diego County Edition pg 1106-E7
Approximate Locationof Proposed StructureHP-5HP-4HP-3HP-2HP-1HP-5Qop6-7QafQop6-7QafQop6-7QafQop6-7QafQop6-7QafQopQaf6-7Old Paralic Deposits( units 6-7 ) GEOLOGIC LEGENDArtificial FillApproximate Locationof Exploratory Handpit20-12942-P5.aiREFERENCE: This Plot Plan was prepared from an existing undated GRADING PLAN providedPASCO LARET SUITER & ASSOCIATES and from on-site field reconnaissance performed by GEI.NOTE: This Plot Plan is not to be used for legalpurposes. Locations and dimensions are approximate.Actual property dimensions and locations of utilitiesmay be obtained from the Approved Building Plansor the “As-Built” Grading Plans.Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.Figure No. IIJob No. 20-12942Scale: 1” =5’(approximate) (Updated)PLOT PLAN ANDSITE SPECIFICGEOLOGIC MAPGARFIELD STREETCHINQUAPIN AVENUE(updated December 2021)LEGEND
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/WEATHERED OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Dense to very dense.
Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 1.5'
106.9
SM
SM
SM
1.2DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
JOB NUMBERSAMPLE
HP-1
DATE LOGGED
± 67' Mean Sea Level
IIIa
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 1.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes medium dense to dense.
-- 16% passing #200 sieve.
SILTY SANDSTONE. Dense to very dense.
Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes mottled, red-brown and light brown.
Bottom @ 4.5'
106.9
102.4
105.7
120.76.4
SM
SM
SM
2.3
2.5
2.2DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
5
JOB NUMBERSAMPLE
HP-2
DATE LOGGED
± 67' Mean Sea Level
IIIb
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 4.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Dense to very dense.Damp. Light gray-brown.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 3.5'
105.6
SM
SM
SM
1.8DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
JOB NUMBERSAMPLE
HP-3
DATE LOGGED
± 64' Mean Sea Level
IIIc
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 3.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)-- becomes medium dense to dense.
SILTY SANDSTONE. Medium dense to dense.
Damp. Light tan.
OLD PARALIC DEPOSITS (Qop 6-7)
-- becomes very dense.
-- 16% passing #200 sieve.
Bottom @ 5'
102.6
SM
SM
SM
2.4DEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
5
6
JOB NUMBERSAMPLE
HP-4
DATE LOGGED
± 61.5' Mean Sea Level
IIId
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
1
2
SILTY SAND , fine- to medium-grained, withroots and organics. Loose. Dry to damp. Light
brown.
FILL/TOPSOIL (Qaf)
SILTY SAND , very porous. Medium dense.
Damp. Light brown.
RESIDUAL SOIL/
WEATHERED
OLD PARALIC DEPOSITS (Qop 6-7)
SILTY SANDSTONE. Medium dense to dense.
Damp. Light tan.
OLD PARALIC DEPOSITS (Qop 6-7)
Bottom @ 3.5'
SM
SM
SMDEPTH (feet)FIGURE NUMBER
20-12942
GROUNDWATER/ SEEPAGE DEPTH
FIELD DESCRIPTION
ANDCLASSIFICATION
10-27-20
1
2
3
4
JOB NUMBERSAMPLE
HP-5
DATE LOGGED
± 59' Mean Sea Level
IIIe
1
SITE LOCATION
JOB NAME
4008 Garfield Street, Carlsbad, CA
Not Encountered
DIMENSION & TYPE OF EXCAVATION
SAMPLE O.D.(INCHES)Garfield Street Residential ProjectSYMBOL BLOWCOUNTS/FT.REVIEWED BY
HE
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
LDR/JAC
LOGGED BYSURFACE ELEVATION
2' X 2' X 3.5' Handpit
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
EQUIPMENT
LOG No.EXPLORATION LOG 12942 GARFIELD-RINCON.GPJ GEO_EXPL.GDT 11/16/20(%)IN-PLACEMOISTURE (%)MAXIMUM DRYDENSITY (pcf)OPTIMUMMOISTURE (%)EXPAN. +CONSOL. -DENSITY(% of M.D.D.)IN-PLACE DRYDENSITY (pcf)U.S.C.S.
75
80
85
90
95
100
105
110
115
120
125
130
135
0 5 10 15 20 25 30 35 40 45
WATER CONTENT, %
MOISTURE-DENSITY RELATIONSHIP
TEST RESULTS
Maximum Dry Density
Optimum Water Content 6.4
Source of Material
Description of Material
DRY DENSITY, pcfSILTY SAND (SM), Brown
ASTM D1557 Method A
HP-2 @ 2.5'
120.7 PCF
%
Curves of 100% Saturationfor Specific Gravity Equal to:
2.80
2.70
2.60
Test Method
Expansion Index (EI)
Figure Number: IV
Job Name: Garfield Street Residential Project
Site Location: 4008 Garfield Street, Carlsbad, CA
Job Number: 20-12942COMPACTION + EI DARK GRID 12942 GARFIELD-RINCON.GPJ GEI FEB06.GDT 11/16/20
L A B O R A T O R Y R E P O R T
Telephone (619) 425-1993 Fax 425-7917 Established 1928
C L A R K S O N L A B O R A T O R Y A N D S U P P L Y I N C.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Sales Order Number: 50003
Account Number: GEOE.R5
To:
*-------------------------------------------------*
Geotechnical Exploration Inc.
7420 Trade Street
San Diego, Ca 92121
Attention: Hector Estrella
Laboratory Number: SO8034-1 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation:
*-------------------------------------------------*
One soil sample received on 11/30/20 at 12:30pm,
from Garfield marked as HP-2@2-4.
Division of Construction, Method for Estimating the Service Life of
Steel Culverts.
pH 7.2
Water Added (ml)Resistivity (ohm-cm)
10 12000
5 9500
5 7700
5 7000
5 5800
5 6000
5 6200
41 years to perforation for a 16 gauge metal culvert.
53 years to perforation for a 14 gauge metal culvert.
73 years to perforation for a 12 gauge metal culvert.
94 years to perforation for a 10 gauge metal culvert.
114 years to perforation for a 8 gauge metal culvert.
Water Soluble Sulfate Calif. Test 417 <0.003%
Water Soluble Chloride Calif. Test 422 0.003%
_______________
Rosa Bernal
RMB/dbb
Analysis By California Test 643, 1999, Department of Transportation
Date: December 9, 2020
Purchase Order Number: GARFIELD
Figure No. IVb
L A B O R A T O R Y R E P O R T
Telephone (619) 425-1993 Fax 425-7917 Established 1928
C L A R K S O N L A B O R A T O R Y A N D S U P P L Y I N C.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Date: December 9, 2020
Purchase Order Number: GARFIELD
Sales Order Number: 50003
Account Number: GEOE.R5
To:
*-------------------------------------------------*
Geotechnical Exploration Inc.
7420 Trade Street
San Diego, Ca 92121
Attention: Hector Estrella
Laboratory Number: SO8034-2 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation:
*-------------------------------------------------*
One soil sample received on 11/30/20 at 12:30pm,
from Garfield marked as HP-4@3-5.
Analysis By California Test 643, 1999, Department of Transportation
Division of Construction, Method for Estimating the Service Life of
Steel Culverts.
pH 6.9
Water Added (ml)Resistivity (ohm-cm)
10 27000
5 17000
5 13000
5 9800
5 8800
5 9100
5 9600
36 years to perforation for a 16 gauge metal culvert.
47 years to perforation for a 14 gauge metal culvert.
65 years to perforation for a 12 gauge metal culvert.
83 years to perforation for a 10 gauge metal culvert.
101 years to perforation for a 8 gauge metal culvert.
Water Soluble Sulfate Calif. Test 417 <0.003%
Water Soluble Chloride Calif. Test 422 0.001%
_______________
Rosa Bernal
RMB/dbb
Figure No. IVc
Garfield Street Condominiums4008 Garfield StreetCarlsbad, CA.SITEFigure No. V Job No. 20-12942EXCERPT FROMNovember 2020Garfield-Condos-2008-geo.aiPacificOcean
APPENDIX A
UNIFIED SOIL CLASSIFICATION CHART
SOIL DESCRIPTION
Coarse-grained (More than half of material is larger than a No. 200 sieve)
GRAVELS, CLEAN GRAVELS GW Well-graded gravels, gravel and sand mixtures, little
(More than half of coarse fraction or no fines.
is larger than No. 4 sieve size, but
smaller than 3”) GP Poorly graded gravels, gravel and sand mixtures, little
or no fines.
GRAVELS WITH FINES GC Clay gravels, poorly graded gravel-sand-silt mixtures
(Appreciable amount)
SANDS, CLEAN SANDS SW Well-graded sand, gravelly sands, little or no fines
(More than half of coarse fraction
is smaller than a No. 4 sieve) SP Poorly graded sands, gravelly sands, little or no fines. SANDS WITH FINES SM Silty sands, poorly graded sand and silty mixtures.
(Appreciable amount)
SC Clayey sands, poorly graded sand and clay mixtures.
Fine-grained (More than half of material is smaller than a No. 200 sieve)
SILTS AND CLAYS
Liquid Limit Less than 50 ML Inorganic silts and very fine sands, rock flour, sandy silt
and clayey-silt sand mixtures with a slight plasticity
CL Inorganic clays of low to medium plasticity, gravelly
clays, silty clays, clean clays.
OL Organic silts and organic silty clays of low plasticity.
Liquid Limit Greater than 50 MH Inorganic silts, micaceous or diatomaceous fine sandy
or silty soils, elastic silts.
CH Inorganic clays of high plasticity, fat clays.
OH Organic clays of medium to high plasticity.
HIGHLY ORGANIC SOILS PT Peat and other highly organic soils
4008 Garfield Street, Carlsbad, CA
Latitude, Longitude: 33.1470, -117.3425
Date 12/10/2021, 8:16:48 AM
Design Code Reference Document ASCE7-16
Risk Category II
Site Class C - Very Dense Soil and Soft Rock
Type Value Description
SS 1.098 MCER ground motion. (for 0.2 second period)
S1 0.396 MCER ground motion. (for 1.0s period)
SMS 1.317 Site-modified spectral acceleration value
SM1 0.594 Site-modified spectral acceleration value
SDS 0.878 Numeric seismic design value at 0.2 second SA
SD1 0.396 Numeric seismic design value at 1.0 second SA
Type Value Description
SDC D Seismic design category
Fa 1.2 Site amplification factor at 0.2 second
Fv 1.5 Site amplification factor at 1.0 second
PGA 0.486 MCEG peak ground acceleration
FPGA 1.2 Site amplification factor at PGA
PGAM 0.583 Site modified peak ground acceleration
TL 8 Long-period transition period in seconds
SsRT 1.098 Probabilistic risk-targeted ground motion. (0.2 second)
SsUH 1.231 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration
SsD 1.5 Factored deterministic acceleration value. (0.2 second)
S1RT 0.396 Probabilistic risk-targeted ground motion. (1.0 second)
S1UH 0.438 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration.
S1D 0.6 Factored deterministic acceleration value. (1.0 second)
PGAd 0.596 Factored deterministic acceleration value. (Peak Ground Acceleration)
CRS 0.892 Mapped value of the risk coefficient at short periods
CR1 0.904 Mapped value of the risk coefficient at a period of 1 s
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