HomeMy WebLinkAboutCDP 2019-0002; HILLSIDE DRIVE RESIDENTIAL; RESPONSE TO CITY OF CARLSBAD THIRD-PARTY GEOTECHNICAL REVIEW; 2020-11-13
13 November 2020
Jessie Smith Job No. 18-11842
447 Bougher Road
San Marcos, CA 92068
Subject: Response to City of Carlsbad Third-Party Geotechnical Review
Smith Residential Lot
4246 Hillside Drive
Carlsbad, California
References: Hetherington Engineering, Inc. 2020, Third-Party Geotechnical Review (first), Proposed
Single-Family Residence 4246 Hillside Drive Carlsbad California. Project No 9142.1 Log
No. 21002 dated June 19, 2020.
Geotechnical Exploration Inc., 2018, Update Report of Preliminary Geotechnical
Investigation, Smith Residential 4246 Hillside Drive Carlsbad, California. Project No. 18-
11842, dated November 09, 2020 (attached).
Dear Mr. Smith:
In accordance with your request, Geotechnical Exploration, Inc. herein responds to the
City of Carlsbad Third-Party Reviewer comments in a memo with completion date June 19,
2020 (Referenced above), with respect to the planned residential project at the subject
property. For clarity purposes we include the comments and responses to them.
Comment No. 1: The Consultant should provide an updated geotechnical report addressing
the plans, and provide updated seismic, grading and foundation recommendations consistent
with the 2019 California Building Code and ASCE 7-16.
Response: Geotechnical Exploration, Inc. has performed an update report of preliminary
geotechnical investigation for the subject project in Carlsbad, California (Attached). The field
work was performed on March 26, 2018, a recent site visit took place on November 10, 2020
to assess the site conditions and determine if they have changed significantly from the first
site visit.
Comment No. 2: The Consultant should review the project grading and foundation plans,
provide any additional geotechnical recommendations considered necessary, and confirm that
the plans have been prepared in accordance with the geotechnical recommendations provided
in the geotechnical report.
Smith Residential Lot Job No. 18-11842
Carlsbad, California Page 2
Response: Geotechnical Exploration Inc., has reviewed the project grading and foundation
plans. The geotechnical recommendations presented in the attached Update Report of
Preliminary Geotechnical Investigation reflect the updated geotechnical recommendations.
Comment No. 3: The Consultant should provide an updated plot plan utilizing the latest
grading plan for the project and providing a) existing topography, b) proposed topography,
c) existing improvements, d) proposed improvements, e) locations of borings/test pits, etc.
Response: The attached Update Report of Geotechnical Investigation includes an updated
plot plan utilizing the latest grading plan provided to this office by the client for the project
and including a) existing topography, b) proposed topography, c) existing improvements, d)
proposed improvements, e) locations of borings/test pits, etc.
Comment No. 4: The Consultant should provide a detailed description of the site.
Response: The attached Update Report of Geotechnical Investigation provides a detailed
description of the site.
Comment No. 5: The Consultant should provide a detailed description of proposed site
grading, structures/improvements, foundation type, etc.
Response: The attached Update Report of Geotechnical Investigation provides a detailed
description of proposed site grading, structures/improvements, foundation type, etc.
Comment No. 6: The Consultant should discuss regional geologic conditions, geologic
structure, and faulting.
Response: The attached Update Report of Geotechnical Investigation provides a discussion
of the regional geologic conditions, geologic structure, and faulting.
Comment No. 7: The Consultant should provide the ASTM standards used for the laboratory
testing.
Response: The attached Update Report of Geotechnical Investigation provides provide the
ASTM standards used for the laboratory testing.
Comment No. 8: The Consultant should provide the site risk category and seismic design
category.
Response: The attached Update Report of Geotechnical Investigation provides site risk
category and seismic design category.
Comment No. 9: The Consultant should provide a statement regarding impact of the
proposed grading and construction on adjacent properties and improvements.
Response: The attached Update Report of Geotechnical Investigation provides a statement
regarding impact of the proposed grading and construction on adjacent properties and
improvements.
Smith Residential Lot Job No. 18-11842
Carlsbad, California Page 3
Comment No. 10: The Consultant should provide grading recommendations.
Response: The attached Update Report of Geotechnical Investigation provides a discussion
and grading recommendations.
Comment No. 10: The Consultant should provide recommendations for temporary
excavations.
Response: The attached Update Report of Geotechnical Investigation provides
recommendations for temporary excavations.
Comment No. 10: The Consultant should provide a statement that the foundation and slab
recommendations (expansive soils) are consistent with the requirements of the Section
1806.6, 2019 California Building Code or revise accordingly.
Response: As noted in Sections IV and V of the attached Update Report of Geotechnical
Investigation, “Based on our visual classification and our past experience with similar soils, it
is our opinion that the existing fill and formational materials of the Old Paralic Deposits, Units
2-4, 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.
Comment No. 11: The recommendations for foundation pressure, lateral bearing pressure,
and lateral sliding resistance exceed the presumptive values for sandy soils included in the
2019 California Building Code and no strength testing was performed. The Consultant should
provide the basis for the recommended values or revise the values accordingly.
Response: The attached Update Report of Geotechnical Investigation provides revised
recommendations for foundation pressure, lateral bearing pressure, and lateral sliding
resistance based on values for sandy soils included in Table 1806.2 of the 2019 California
Building Code.
Comment No. 12: The Consultant should address expected total and differential settlement
due to soil and foundation loads.
Response: The attached Update Report of Geotechnical Investigation addresses the
expected total and differential settlement due to soil and foundation loads.
Comment No. 13: The Consultant should provide hardscape recommendations (thickness,
reinforcement, joints, etc.).
Response: The attached Update Report of Geotechnical Investigation provides hardscape
recommendations (thickness, reinforcement, joints, etc.).
Comment No. 14: The Consultant should specify the sulfate exposure category (ACI 318)
based on soluble sulfate testing and provide recommendations for sulfate resistant concrete,
if necessary, or default to a severe exposure category, if testing is not available.
Smith Residential Lot Job No. 18-11842
Carlsbad, California Page 4
Response: Geotechnical Exploration Inc., recommends that a soluble sulfate testing be
performed of the near surface soils to be in contact with foundations and concrete elements
after grading is completed, to determine the sulfate exposure category and recommend the
appropriate sulfate resistant concrete prior to pouring concrete. Alternatively, if those
chemical tests are not performed, with have recommended to use concrete with a
compressive strength of 4,500 psi, cement type V, water cement ratio no higher than 0.40.
Comment No. 15: The Consultant should provide a list of recommended observation and
testing during site grading and construction.
Response: The attached Update Report of Geotechnical Investigation provides a discussion
and a list of recommended observation and testing during site grading and construction.
Comment No. 16: The Consultant should provide a list of published maps/reports used in
the preparation of the report.
Response: The attached Update Report of Geotechnical Investigation provides list of
published maps/reports used in the preparation of the report.
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. 18-11842 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
UPDATE REPORT OF PRELIMINARY GEOTECHNICAL
INVESTIGATION
Smith Residential Lot
4246 Hillside Drive
Carlsbad, California
Job No. 18-11842
13 November 2020
Prepared for:
Jessie Smith
13 November 2020
Jessie Smith Job No. 18-11842
447 Bougher Road
San Marcos, CA 92068
Subject: Update Report of Preliminary Geotechnical Investigation
Smith Residential Lot
4246 Hillside Drive
Carlsbad, California
Dear Mr. Smith:
In accordance with your request, Geotechnical Exploration, Inc. has performed
an update report of preliminary geotechnical investigation for the subject project in
Carlsbad, California. The field work was performed on March 26, 2018.
If the conclusions and recommendations presented in this report are incorporated
into the design and construction of the proposed single-family residential structure
with attached garage, concrete driveway 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. 18-11842 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
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 ..................................................... 6
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION ................................... 11
VIII. GEOLOGIC HAZARDS ........................................................................ 12
A. Local and Regional Faults ........................................................... 13
B. Other Geologic Hazards ............................................................. 17
IX. GROUNDWATER ............................................................................... 21
X. CONCLUSIONS & RECOMMENDATIONS ................................................ 23
A. Preparation of Soils for Site Development ..................................... 24
B. Seismic Design Criteria .............................................................. 34
C. Foundation Recommendations .................................................... 35
D. Concrete Slab On-Grade Criteria ................................................. 38
E. Retaining Wall Design Criteria ..................................................... 42
F. Slopes .................................................................................... 45
G. Pavements .............................................................................. 46
H. Site Drainage Considerations ...................................................... 47
I. General Recommendations ......................................................... 49
XI. GRADING NOTES .............................................................................. 50
XII. LIMITATIONS ................................................................................... 51
REFERENCES
FIGURES
I. Vicinity Map
II. Plot Plan
IIIa-d. Exploratory Boring Logs and Laboratory Results
IV. 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
Update Report of Preliminary Geotechnical Investigation
Smith Residential Lot
4246 Hillside Drive
Carlsbad, California
JOB NO. 18-11842
The following report presents the findings and recommendations of Geotechnical
Exploration, Inc. for the subject project.
I. PROJECT SUMMARY
This update report is prepared in response to the City of Carlsbad third-party reviewer
comments dated June 19, 2020. It is our understanding, based on our
communications with the client that the project will consist of the improvement of
the existing undeveloped lot to accommodate a new single-family residential
structure and associated improvements, which will make use of retaining walls,
continuous footings and slab on grade. It is also our understanding that the proposed
residential structure is to be constructed along the eastern portion of the property
with an access driveway off of Hillside Drive to the west.
As part of our investigation, we observed and evaluated the soil conditions at four
locations within the proposed new building areas. The new structure is to be
constructed of standard-type building materials utilizing conventional foundations
with either concrete slab on-grade or raised wood floors. Foundation loads are
expected to be typical for this type of relatively light construction. A preliminary site
plan by Benlund Engineering (undated), has been reviewed by us and used to
understand the scope of the project. We have also reviewed structural plans by DCI
Engineers dated June 11, 2018. If the plans are modified, they should be made
available for our review. Additional or modified recommendations will be provided at
that time if warranted.
Smith Residential Lot Job No. 18-11842
Carlsbad, California Page 2
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.
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 four 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. 207-022-11, in the City of Carlsbad, County
of San Diego, State of California. For the purposes of this report, the proposed
residence is assumed to face westward to Hillside Drive but, in fact, faces west-
southwestward. Refer to Figure No. I, the Vicinity Map, for the site location.
The generally rectangular shaped lot, consisting of 213,282 square feet, is bordered
on the north and south by single-family residential developments at street elevations;
on the west by Hillside Drive; and on the east by single-family residential properties.
Refer to Figure No. II, the Plot Plan.
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Carlsbad, California Page 3
A recent site visit (November 10, 2020) reveals that the existing property is currently
undeveloped; vegetation on the site consists primarily seasonal grasses natural
shrubs and weeds.
The middle of the property has a depression at an approximate elevation of +92 feet
above MSL. From that point the property ascends to the north, south and east to the
adjacent single-family residential properties and ascends to the west to Hillside Drive.
Approximate elevations across the property range from approximately +118 feet
above MSL along the western property line of the site to approximately +116 feet
above MSL at the eastern property line; and elevations of +100 feet and +102 feet
above MSL along the north and south property lines, respectively. Survey
information concerning elevations across the site was obtained from the topographic
survey template of the preliminary site plan by Benlund Engineering, undated (see
Plot Plan, Figure No. II).
IV. FIELD INVESTIGATION, OBSERVATIONS & SAMPLING
The field work, conducted on March 26, 2018, consisted of a surface reconnaissance
and a subsurface exploration program excavating and logging four exploratory test
pits in the location of the proposed new residence, driveway and improvements. The
excavations revealed that the building site is underlain by approximately 1.5 to 6 feet
of loose to medium dense, silty/clayey sand fill soil over medium dense to dense,
silty sand formational materials. The on-site soils are considered to have a low
expansion potential with an Expansion Index of less than 50. The soils encountered
in the exploratory trenches 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, the Plot Plan.
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Carlsbad, California Page 4
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-d.
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-d and IV. The following tests were conducted on representative soil samples:
1. Laboratory Compaction Characteristics (ASTM D1557-12e1)
2. Determination of Percentage of Particles Smaller than #200 Sieve
(ASTM D1140-17)
The test results are presented on the trench logs at the appropriate sample depths
and laboratory test results.
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Carlsbad, California Page 5
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. 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
91 to 130 High
Above 130 Very high
Based on our visual classification and our past experience with similar soils, it is our
opinion that the existing fill and formational materials of the Old Paralic Deposits,
Units 2-4, 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.
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Carlsbad, California Page 6
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 of 33
degrees and cohesion equal to 50 psf, as well as total unit weight of 120 pcf are
based on the soil visual inspection and our experience.
With these values we calculated the ultimate bearing capacity of the soil to be 9285
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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Carlsbad, California Page 7
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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Carlsbad, California Page 8
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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Carlsbad, California Page 9
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.
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Carlsbad, California Page 10
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
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
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Carlsbad, California Page 11
shaking near the epicenter. It was followed by more than 60 aftershocks of M1.3
and greater during the first hour.
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 2-4 (Qop2-4) 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 approximately 1.5 to 6 feet of
loose to medium dense artificial fill soils (Qaf). Site-specific geology is mapped on
Figure No. II, the Plot Plan.
Fill Soil (Qaf): As noted above, the areas of our exploratory excavations are mantled
by approximately 1.5 to 6 feet of fill soil. The encountered fill soil consists of fine- to
medium-grained, damp, red-brown to dark-brown, silty sands (SM) with variable
amounts of roots and rock fragments. The fill soils are loose to medium dense. 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-d for details.
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Carlsbad, California Page 12
Old Paralic Deposits, Unit 2-4 (Qop2-4): Formational materials of Old Paralic Deposits,
Units 2-4 were encountered in all trenches underlying the fill soil at variable depths
from 1.5 to 6 feet. The formational materials consist of fine- to medium-grained,
damp to wet, red-brown silty sands (SM) with areas of moderate cementation and
some roots. The formational materials underlying the site are medium dense to
dense. In our opinion, the medium dense to dense nature of the Old Paralic Deposits,
Units 2-4, makes it suitable in its current condition to support loads from structures
or additional fill. Refer to Figure Nos. IIIa-d 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 2-4,
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. IV, 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. In our explicit professional
opinion, neither an active fault nor a potentially active fault underlies the site.
Newport-Inglewood-Rose Canyon Fault Zone: The Oceanside section of the Newport-
Inglewood-Rose Canyon Fault Zone is mapped approximately 5 miles west-southwest
of the site at its closest point. This fault zone is mapped as trending north-south
from Oceanside to downtown San Diego, from where it appears to head southward
into San Diego Bay, through Coronado and offshore. The Rose Canyon Fault Zone is
considered to be a complex zone of onshore and offshore, en-echelon strike slip,
oblique reverse, and oblique normal faults. The Rose Canyon 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 RCFZ 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
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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.
Coronado Bank Fault Zone: The Coronado Bank - Palos Verdes section of the
Coronado Bank Fault Zone is mapped as located approximately 22.7 miles west of
the site at its closest point. 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.
Elsinore Fault: The Temecula and Julian sections of the Elsinore Fault Zone are
located approximately 23 and 33 miles northeast and east of the site respectively.
The fault extends approximately 200 km (125 miles) from the Mexican border to the
northern end of the Santa Ana Mountains and is divided in several sections. 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.
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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
is a 11 percent probability that an earthquake of M6.7 or greater will occur within 30
years on this fault.
San Jacinto Fault Zone: The Anza and Coyote Creek sections of the San Jacinto Fault
is located approximately 50 to 53 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
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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
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:
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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.
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
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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), indicate there are no known or
suspected ancient landslides located on the site.
Slope Stability: We performed a site reconnaissance and the site slopes gently
descending from Hillside Drive in an easterly direction was measured; from the
available survey map to incline in an approximately 2.8:1.0 (horizontal to vertical).
The eastern ascending slope was measured at approximately 4.0:1.0 (horizontal to
vertical). The site is underlain by relatively stable Old Paralic Deposits, Unit 2-4
formational materials at a depth of 1½ to 6 feet. In our opinion, there is not a slope
stability issue with the site.
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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, saturated sands and silts when they are sufficiently shaken by an
earthquake. On this site, the risk of liquefaction of formational materials due to the
medium dense to 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. As such, liquefaction induced hazards like lateral
spreading, ground lurching and seismic dynamic settlement, are also considered
negligible.
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.
The site is located approximately 1.1 miles from the exposed coastline and at an
elevation of approximately 100 to 116 feet above MSL. There is no risk of tsunami
inundation at the site.
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A seiche is a run-up of water within a lake or embayment triggered by fault- or
landslide-induced ground displacement. The Agua Hedionda body of water is located
at approximately 0.33-mile to the southwest as noted previously the site’s elevations
are approximately +100 to +116 feet above MSL as such it is our opinion that the
possibility of a seiche to affect the subject site is negligible to nonexistent.
Flood Hazard: Based on 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. This statement should
be verified with the County of San Diego (FEMA, 2012).
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, ADUs, retaining walls and associated improvements
provided the recommendations herein are implemented. Furthermore, based on the
available information at this stage, it is our opinion that 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.
No significant geologic hazards are known to exist on the site that would prohibit the
construction of the proposed residential structure 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.
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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 borings to the maximum
depths explored. A more detailed description of the subsurface materials
encountered in our exploratory excavations Figure Nos. IIIa-d.
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.
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
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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-
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.
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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 review of the available references
and proposed construction plans provided to this office during the execution of our
investigation, practical field exploration conducted by our firm, and resulting
laboratory tests, in conjunction with our knowledge and experience with similar soils
in the Carlsbad area. Foundation plans were not available at this time, as such we
recommend that the foundation plans be designed based on the recommendations
presented herein.
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.
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.
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We recommend that the planned residential structure, garage, 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 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 removed and recompacted during
grading to create a building pad and to construct the proposed driveway descending
from Hillside Drive. The existing fill soils are not suitable in their current condition to
support new structures or associated improvements. A full removal and
recompaction of existing fill and top 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.
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 and/or County of San Diego.
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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: 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
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, topsoil and upper weathered formational soils should be
removed and recompacted. The depth of removals across the site will vary
depending on the thickness of unsuitable soils overlying the formational
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materials. It is anticipated that the depth of removal will be up to 6 feet below
existing grade area of the existing house and garage pad (in the general
vicinity of the exploratory excavation HP-2), however, shallower removal
should 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
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.
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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 8 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
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).
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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
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.
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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. After rough grading completion,
representative soil samples from subgrade soils should be tested for soluble
sulfates, chlorides, and Ph to determine their aggressivity to attack concrete
and steel. Otherwise, Type V cement and water cement ratio not higher than
0.40 should be used in concrete, with a minimum compressive strength of
4,500 psi.
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;
d) Verify use of proper materials, densities and ft thicknesses during
placement and compaction of compacted fill prior to placement of
compacted fill, inspect subgrade and verify that site has been prepared
properly
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Section 1705.6 “Soils” statement and Table 1705.6 indicates 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,
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
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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
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
potential problems such as damage to project improvements that could
result from construction on undocumented fill soils.
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• 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.
• All approved changes will then be transferred to the mylars for approval
and signatures by the Deputy City Engineer.
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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. Request 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 Databases: 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 33.151385 degrees and a longitude
of -117.327236 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 Stiff Soils D.
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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
1.043 0.378 1.13 0.725 0.753g 0.484 1.083 1.919 0.459 0.523g 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. 5, 6 and 7.
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.
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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 pounds per square foot (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.
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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. 3 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.
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. Control joints
and reinforcement should be specified by the structural engineer.
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 provided preliminary plans indicate
the construction of variable height retaining walls up to 6 feet in elevation
surrounding the proposed residential structure and driveway. These retaining
wall may be designed with stepped foundations bearing in properly approved
compacted fill or preferably on dense formational soils. 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 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
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surcharge to horizontal uniform pressure. For passive resistance, use the
value of 750 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
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 12 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.
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25. Basement/Retaining Wall Drainage: The preceding design pressures assume
that the walls are backfilled with 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.
Backfill placed behind retaining walls should be compacted to a minimum
degree of compaction of 95 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.
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F. Slopes
24. Temporary Slopes: Based on our subsurface investigation work, laboratory
test results, and engineering analysis, slopes of approximately 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 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.
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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: The referenced grading plans prepared by Benlund
Engineering, indicate the construction of permanent fill slopes of up to
approximately 12 feet to accommodate the proposed new driveway off Hillside
Drive. Prior to construction of this driveway approach, all existing
undocumented fill should be removed and replaced with property compacted,
tested and approved fill following the compaction recommendations presented
in Section A “Preparation of Soils for Site Development”. 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 concrete paving. The concrete should
conform to Section 201 of The Standard Specifications for Public Works
Construction, 2015 Edition, for Class 560-C-3250.
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In order to control shrinkage cracking, we recommend that saw-cut,
weakened-plane joints be provided at about 15-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-feet. 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
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
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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
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
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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.
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
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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 "Update 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
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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.
Smith Residential Lot Job No. 18-11842
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. 18-11842 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. 18-11842
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.
Benlund Engineering, Undated Grading Plans for Smith Residence. Project No. CDP2019-0002, Drawing
No. 512-6A
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.
FEMA, 2019, Flood Map number 06073C0764H effective on 12/20/2019,
https://msc.fema.gov/portal/home
Geotechnical Exploration Inc., 2018, Preliminary Geotechnical Investigation, Smith Residential Lot
South of 4240 Hillside Drive Carlsbad, California. Project No. 18-11842, dated April 09, 2018.
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.
Hetherington Engineering, Inc. 2020, Third-Party Geotechnical Review (first), Proposed Single-Family
Residence 4246 Hillside Drive Carlsbad California. Project No 9142.1 Log No. 21002 dated June 19,
2020.
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.
REFERENCES/Page 2
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.
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
SITESITESITE
Smith Residence
4246 Hillside Drive
Carlsbad, CA.
Figure No. I
Job No. 18-11842
Thomas Bros Guide San Diego County pg 1106-G6
Assumed PropertyBoundaryApproximate Locationof Exploratory HandpitHP-1HP-2HP-3HP-4HP-4(updated October 2020)Smith Residence 4246 Hillside DriveCarlsbad, CA.Figure No. IIJob No. 18-1184218-11842-p3.aiLEGENDSCALE: 1” = 20’(approximate)PLOT PLANREFERENCE: This Plot Plan was prepared from an existing undatedGRADING PLAN by BENLUND ENGINEERING and from on-site field reconnaissance performed by GEI.NOTE: This Plot Plan is not to be used for legalpurposes. Locationss and dimensions are approximate.Actual property dimensions and locations of utilitiesmay be obtained from the Approved Building Plansor the “As-Built” Grading Plans.ExistingDrivewayHouseDrainHILLSIDE
D
R
I
V
EDrainageGarage
SILTY SAND , fine- to medium-grained, withroots and rock fragments. Loose to medium
dense. Dry. Dark brown.
FILL (Qaf)
SILTY SAND , fine- to medium-grained;
moderately cemented. Medium dense to dense.
Dry to damp. Light gray.
OLD PARALIC DEPOSITS (Qop 2-4)
Bottom @ 4'
SM
SM
Vacant Lot - South of 4240 Hillside Dr., Carlsbad, CA1
SITE LOCATION
JKH
SAMPLELOGGED BY
DEPTH (feet)FIGURE NUMBER
18-11842
GROUNDWATER/ SEEPAGE DEPTH
JOB NUMBER
EQUIPMENT
LOG No.
FIELD DESCRIPTION
ANDCLASSIFICATION
IIIa
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
JOB NAME
3-26-18
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
± 115' Mean Sea Level Not Encountered
HP-1
DATE LOGGED
1
2
3
4
5 SYMBOLSURFACE ELEVATION
3' X 3' X 4' Handpit
SAMPLE O.D.(INCHES)Smith Residence BLOWCOUNTS/FT.LDR/JAC
DIMENSION & TYPE OF EXCAVATION
REVIEWED BY
EXPLORATION LOG 11842 SMITH.GPJ GEO_EXPL.GDT 4/9/18DENSITY(% of M.D.D.)(%)U.S.C.S.IN-PLACEMOISTURE (%)OPTIMUMMOISTURE (%)MAXIMUM DRYDENSITY (pcf)IN-PLACE DRYDENSITY (pcf)EXPAN. +CONSOL. -
SILTY SAND , fine- to medium-grained, withsome roots. Loose to medium dense. Damp.
Red-brown.
FILL (Qaf)
-- becomes dark red-brown with white sandstonefragments.
Hand auger from 3'- 7'.
-- 24% passing #200 sieve.
SILTY SAND , fine- to medium-grained;moderately cemented. Medium dense to dense.Damp. Light gray and red-brown.
OLD PARALIC DEPOSITS (Qop 2-4)
Bottom @ 7'
123.3
8098.0
11.5
SM
SM
9.2
Vacant Lot - South of 4240 Hillside Dr., Carlsbad, CA1
SITE LOCATION
JKH
SAMPLELOGGED BY
DEPTH (feet)FIGURE NUMBER
18-11842
GROUNDWATER/ SEEPAGE DEPTH
JOB NUMBER
EQUIPMENT
LOG No.
FIELD DESCRIPTION
ANDCLASSIFICATION
IIIb
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools, Hand Auger
JOB NAME
3-26-18
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
± 105' Mean Sea Level Not Encountered
HP-2
DATE LOGGED
1
2
3
4
5
6
7
8 SYMBOLSURFACE ELEVATION
3' X 3' X 7' Handpit/ Auger Hole
SAMPLE O.D.(INCHES)Smith Residence BLOWCOUNTS/FT.LDR/JAC
DIMENSION & TYPE OF EXCAVATION
REVIEWED BY
EXPLORATION LOG 11842 SMITH.GPJ GEO_EXPL.GDT 4/9/18DENSITY(% of M.D.D.)(%)U.S.C.S.IN-PLACEMOISTURE (%)OPTIMUMMOISTURE (%)MAXIMUM DRYDENSITY (pcf)IN-PLACE DRYDENSITY (pcf)EXPAN. +CONSOL. -
SILTY SAND , fine- to medium-grained, withsome roots. Loose to medium dense. Damp. Dark
brown.
FILL (Qaf)
SILTY SAND , fine- to medium-grained;
moderately well cemented. Dense. Damp.
Red-brown.
OLD PARALIC DEPOSITS (Qop 2-4)
Bottom @ 3'
SM
SM
Vacant Lot - South of 4240 Hillside Dr., Carlsbad, CA1
SITE LOCATION
JKH
SAMPLELOGGED BY
DEPTH (feet)FIGURE NUMBER
18-11842
GROUNDWATER/ SEEPAGE DEPTH
JOB NUMBER
EQUIPMENT
LOG No.
FIELD DESCRIPTION
ANDCLASSIFICATION
IIIc
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
JOB NAME
3-26-18
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
± 94' Mean Sea Level Not Encountered
HP-3
DATE LOGGED
1
2
3
4
5 SYMBOLSURFACE ELEVATION
3' X 3' X 3' Handpit
SAMPLE O.D.(INCHES)Smith Residence BLOWCOUNTS/FT.LDR/JAC
DIMENSION & TYPE OF EXCAVATION
REVIEWED BY
EXPLORATION LOG 11842 SMITH.GPJ GEO_EXPL.GDT 4/9/18DENSITY(% of M.D.D.)(%)U.S.C.S.IN-PLACEMOISTURE (%)OPTIMUMMOISTURE (%)MAXIMUM DRYDENSITY (pcf)IN-PLACE DRYDENSITY (pcf)EXPAN. +CONSOL. -
SILTY SAND , fine- to medium-grained, withsome roots and rock fragments. Loose to medium
dense. Damp. Dark brown.
FILL (Qaf)
-- becomes red-brown.
SILTY SAND , fine- to medium-grained;
moderately well cemented. Medium dense todense. Damp. Red-brown.
OLD PARALIC DEPOSITS (Qop 2-4)
Bottom @ 4'
SM
SM
Vacant Lot - South of 4240 Hillside Dr., Carlsbad, CA1
SITE LOCATION
JKH
SAMPLELOGGED BY
DEPTH (feet)FIGURE NUMBER
18-11842
GROUNDWATER/ SEEPAGE DEPTH
JOB NUMBER
EQUIPMENT
LOG No.
FIELD DESCRIPTION
ANDCLASSIFICATION
IIId
DESCRIPTION AND REMARKS
(Grain size, Density, Moisture, Color)
Hand Tools
JOB NAME
3-26-18
PERCHED WATER TABLE
BULK BAG SAMPLE
IN-PLACE SAMPLE
MODIFIED CALIFORNIA SAMPLE
NUCLEAR FIELD DENSITY TEST
STANDARD PENETRATION TEST
± 105' Mean Sea Level Not Encountered
HP-4
DATE LOGGED
1
2
3
4
5 SYMBOLSURFACE ELEVATION
3' X 3' X 4' Handpit
SAMPLE O.D.(INCHES)Smith Residence BLOWCOUNTS/FT.LDR/JAC
DIMENSION & TYPE OF EXCAVATION
REVIEWED BY
EXPLORATION LOG 11842 SMITH.GPJ GEO_EXPL.GDT 4/9/18DENSITY(% of M.D.D.)(%)U.S.C.S.IN-PLACEMOISTURE (%)OPTIMUMMOISTURE (%)MAXIMUM DRYDENSITY (pcf)IN-PLACE DRYDENSITY (pcf)EXPAN. +CONSOL. -
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 11.5
Source of Material
Description of Material
DRY DENSITY, pcfSILTY SAND (SM), Red-brown
ASTM D1557 Method A
HP-2 @ 3.0'
123.2 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: Smith Residence
Site Location: Vacant Lot - South of 4240 Hillside Dr., Carlsbad, CA
Job Number: 18-11842COMPACTION + EI DARK GRID 11842 SMITH.GPJ GEI FEB06.GDT 4/9/18
REGIONAL GEOLOGIC MAP
(Excerpt)
Proj No.:18-11842
Figure V.
PROPOSED SMITH RESIDENCE
4246 HILLSIDE DR.
CARLSBAD, CA
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
11/9/2020 U.S. Seismic Design Maps
https://seismicmaps.org 1/3
4246 Hillside Dr., Carlsbad CA
4246 Hillside Dr, Carlsbad, CA 92008, USA
Latitude, Longitude: 33.1513481, -117.3272935
Date 11/9/2020, 11:28:43 AM
Design Code Reference Document ASCE7-16
Risk Category II
Site Class D - Stiff Soil
Type Value Description
SS 1.043 MCER ground motion. (for 0.2 second period)
S1 0.378 MCER ground motion. (for 1.0s period)
SMS 1.13 Site-modified spectral acceleration value
SM1 null -See Section 11.4.8 Site-modified spectral acceleration value
SDS 0.753 Numeric seismic design value at 0.2 second SA
SD1 null -See Section 11.4.8 Numeric seismic design value at 1.0 second SA
Type Value Description
SDC null -See Section 11.4.8 Seismic design category
Fa 1.083 Site amplification factor at 0.2 second
Fv null -See Section 11.4.8 Site amplification factor at 1.0 second
PGA 0.459 MCEG peak ground acceleration
FPGA 1.141 Site amplification factor at PGA
PGAM 0.523 Site modified peak ground acceleration
TL 8 Long-period transition period in seconds
SsRT 1.043 Probabilistic risk-targeted ground motion. (0.2 second)
SsUH 1.165 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration
SsD 1.5 Factored deterministic acceleration value. (0.2 second)
S1RT 0.378 Probabilistic risk-targeted ground motion. (1.0 second)
S1UH 0.417 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration.
S1D 0.6 Factored deterministic acceleration value. (1.0 second)
PGAd 0.534 Factored deterministic acceleration value. (Peak Ground Acceleration)
CRS 0.895 Mapped value of the risk coefficient at short periods
11/9/2020 U.S. Seismic Design Maps
https://seismicmaps.org 2/3
Type Value Description
CR1 0.907 Mapped value of the risk coefficient at a period of 1 s
11/9/2020 U.S. Seismic Design Maps
https://seismicmaps.org 3/3
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