HomeMy WebLinkAboutSDP 2023-0025; GRAND HOPE MEDICAL OFFICE; PRELIMINARY GEOTECHNICAL INVESTIGATION; 2023-07-27TABLE 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 ...................................................... 7
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION ..................................... 7
A. Stratigraphy ................................................................................ 7
B. Structure .................................................................................... 9
VIII. GEOLOGIC HAZARDS ........................................................................... 9
A. Local and Regional Faults ............................................................ 10
B. Other Geologic Hazards .............................................................. 11
IX. GROUNDWATER ................................................................................ 14
X. CONCLUSIONS & RECOMMENDATIONS ................................................. 16
A. Preparation of Soils for Site Development ...................................... 17
8. Seismic Design Criteria ............................................................... 24
C. Foundation Recommendations .... , ........................ , , ...................... 26
D. Concrete Slab On-Grade Criteria .................................................. 28
E. Retaining Wall Design Criteria ..................................................... , 30
F. Temporary Slopes ...................................................................... 32
G. Pavements .................................................................. , ............ , 33
H. Site Drainage Considerations ................................................ ,, ..... 33
I. General Recommendations ....................... ,, ................................. 35
XI. GRADING NOTES ............................................................................... 36
XII. LIMITATIONS .................................................................................... 37
REFERENCES
FIGURES
I. Vicinity Map
II. Plot Plan with Site Specific Geologic Map
llla-e. Exploratory Excavation Logs
IVa-c. Laboratory Data
V. Geologic Map Excerpt and Legend
APPENDICES
A. Unified Soil Classification System
B. Regional Geologic Descriptions
C. ASCE Seismic Summary Report
D. Slab Moisture Information
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It is also our explicit opinion, based on our field investigation, review of pertinent
geologic literature and analysis of geological maps, that neither an active nor a
potentially active fault or landslide underlies the subject site.
II. SCOPE OF WORK
The scope of work performed for this investigation was based on the Conceptual Site
Plan prepared by Kirk Moeller Architects, Inc., dated July 27, 2023. Our work
included site observations and a subsurface exploration program under the direction
of our geologist, with placement, logging and sampling of five (5) exploratory
excavations utilizing hand tools and a thin-walled hand driven sampler. In addition,
we reviewed available published information pertaining to site geology, evaluated the
bearing characteristics of the encountered surficial fill and formational material,
performed geotechnical engineering analysis of the field data, and prepared this
report.
The data obtained and the analyses performed were for the purpose of providing
geotechnical design parameters, recommendations, and construction criteria for the
development of the proposed new medical office building structure and associated
improvements.
III. SITE DESCRIPTION
The site is more particularly known as Assessor's Parcel No. 203-202-13-00, Lot 26
of Carlsbad Tract Map No. 2145, and is located at 2879-2885 Hope Avenue in
Carlsbad, California. Refer to Figure No. I, the Vicinity Map, for the site location.
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Representative soil samples were obtained from the exploratory hand pits at selected
depths appropriate to the investigation. Soil sampling included in-place samples and
bulk samples collected from the exploratory hand pits to aid in classification and for
appropriate laboratory testing, All samples were returned to our laboratory for
evaluation and testing.
Exploratory hand pit logs have been prepared based on our observations and
laboratory test results and are attached as Figure Nos. IIIa-e. The exploratory hand
pit logs and related information reveal 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
explored locations. Also, the passage of time may result in changes in the subsurface
conditions due to environmental changes.
V. LABORATORY TESTING & SOIL INFORMATION
Laboratory tests were performed on the soil samples in order to evaluate their
physical and mechanical properties and their ability to support the proposed new
medical building and associated improvements. The test results are presented at
their respective depths on Figure Nos. II!a-e and IVa-c. The following tests were
conducted on representative soil samples:
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1. Moisture Content (ASTM D2216-19)
2. Density Measurements (ASTM D2937-17e2)
3. Standard Test Method for Bulk Specific Gravity and Density of Com-
pacted Bituminous Mixtures using Coated Samples (ASTM D1188-07)
4, Laboratory Compaction Characteristics (ASTM D1557-12e1)
5. Determination of Percentage of Particles Smaller than # 200
Sieve (ASTM D1140-17)
6. Expansion Index (ASTM D4829-19)
7. Resistivity and pH Analysis (Department of Transportation
California Test 643)
8. Water Soluble Sulfate (Dept of Transportation California Test 417)
9. Water Soluble Chloride (Dept of Transportation California Test 422)
Moisture content and density measurements were performed by ASTM methods
D2216-19 and D2937-17e2 respectively, in conjunction with D1188-07 to establish
the in-situ moisture and density of samples retrieved from the exploratory
excavations. Density measurements were also performed by ASTM method D1188-
07, the bulk specific gravity utilizing paraffin-coated specimens. This method helps
to establish the in-situ density of chunk samples retrieved from the excavations. The
test results are presented on the handpit logs at the appropriate sample depths.
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 handpit logs at the appropriate sample depths and on Figure No. IV, 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
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concrete and ferrous metals. Refer to Recommendation No. 7 and Figure No. IVc for
test results.
VI. REGIONAL GEOLOGIC PESCRipJION
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
Peninsular Ranges with primarily Cenozoic sedimentary rocks to the west and east of
this central mountain range (Demere, 1997).
descriptions, refer to Appendix B.
For more detailed geologic
VII. SITE-SPECIFIC SOIL & GEOLOGIC DESCRIPTION
Review of the Geologic Map of Oceanside, 30'x60' Quadrangle, CA by Kennedy and
Tan, 2007, ind'1cates that the subject site is located in an area underlain by Old Paralic
Deposits (Qop5-7). An excerpt of this geologic map and legend is included as Figure
No. V.
A. stratiaraDhv
Our field investigation, reconnaissance, and review of the geologic map by Kennedy
and Tan, 2007, "Geologic Map of the Oceanside 30'x60' Quadrangle, California"
indicate that the site is underlain at depth by late to middle Pleistocene-Aged Old
Paralic Deposits, Units 6-7 (Qop6-7) formational materials. The geologic map
indicates that the Para lie Deposits are underlain at depth by the Tertiary-age Santiago
Formation (Tsa). An excerpt of the geologic map is included as Figure No. V. Our
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exploratory handpits indicate the formational materials are overlain across the site
by a thin veneer of artificial fill soils (Qaf). Site-specific geology is shown on Figure
No. II, the Plot Plan and Site-Specific Geologic Map.
Fill Soil (Oaf): Our site investigation indicates that the areas in the general vicinity
of our exploratory handpits at the site are overlain by 1 to 1.5 feet of fill soil. The
encountered fill soil consists of slightly moist to moist, brown to dark brown, fine-to
medium-grained silty sand (SM). The fill soils are generally medium dense with some
loose areas. In our opinion, due to the variable density 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. Illa-e for details.
Old paralic Deposits, Unit 6-7 (Qop6.zl;_ The encountered formational materials are
described in the literature as Quaternary (late to middle Pleistocene) Old Paralic
Deposits, Units 6-7. These formational materials were encountered in handpits HP-
1 through HP-5 underlying the fill soil at depths from 1 to 1.5 feet. The formational
materials consist of fine-to medium-grained, damp to moist, red-brown silty sands
(SM) with some iron oxide/manganese nodules. The formational Old Paralic materials
underlying the site are medium dense and become dense at approximately 2.5 feet
in depth. In our opinion, the dense nature of the Old Paralic Deposits, Units 6-7,
makes it suitable in its current condition to support loads from structures or additional
fill. Refer to Figure Nos. Illa-e for details.
A review of the "Geologic Map of the Oceanside 30'x60' Quadrangle, California" by
Kennedy and Tan, 2007, indicates that the Old Paralic Deposits, Units 6-7,
formational materials underlie the entire site at depth. The aforementioned Old
Paralic Deposit Units are described as "Poorly sorted, moderately permeable, reddish-
brown, interfingered strandline, beach, estuarine and colluvial deposits composed of
siltstone, sandstone and conglomerate." According to the map, there are no faults
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known to pass through the site (refer to Figure No. V, Geologic Map Excerpt and
Legend).
8. Structure
Visible geologic structure was not identified during our field investigation. The Old
Paralic Deposits (Qop6-1) formation was noted to be massive in our exploratory
excavations. As shown on the geologic map the Old Paralic Deposits are underlain
at depth by the Tertiary Santiago Formation (Tsa). The essentially horizontal contact
of Old Paralic Deposits over the Santiago Formation indicates no significant structural
deformation has occurred in the area of the project. It is our opinion that the geologic
structure of the site does not represent a hazard to the site and is stable from a
geotechnical perspective.
VIII. GEOLOGIC HAZARDS
Our field work, as well as the references cited, indicate a favorable geologic structure
at the site. Based on our reconnaissance and the data obtained in our field
investigation, review of pertinent geological literature and analysis of geological maps
and aerial photographs, it is our opinion that the area of study has favorable geologic
structure and is low risk from a geologic hazard perspective. There are no known
active landslide deposits underlying the site. Based on review of available geologic
and fault hazards maps and reports, it is our opinion that neither an active nor
potentially active fault underlies the site in the area of the proposed new medical
office building structure and improvements.
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 Reaional 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. As noted previously, in our
professional opinion, neither an active fault nor a potentially active fault underlies
the site in the area of the proposed construction.
A brief description of the nearby active faults, including distances from the mapped
fault to the subject site at the closest point (based on the USGS Earthquake Hazards-
Interactive Fault Map), is presented below.
• Rose Canyon Fault Zone: Mapped approximately 5.3 miles northwest of the site,
considered capable of a M6.9 earthquake (Singleton et al., 2019; EERI, 2021).
• Newport-Inglewood Fault Zone: The Oceanside section of the Newport-
Inglewood fault is mapped approximately 5.2 miles west of the site, estimated
to be capable of producing a M6.0 to M7.4 earthquake (Grant Ludwig and
Shearer, 2004; SCEDC, 2022).
• Coronado Bank Fault Zone: Mapped approximately 21.3 miles west-southwest
of the site, estimated to be to be capable of a M7 .6 earthquake.
• Elsinore Fault Zone: Mapped approximately 24 miles northeast of the site,
estimated to be capable of a M6.0 to M7.0 (Rockwell et al. 1985) and M7.S
(Greensfelder, 1974).
•
•
San Diego Trough Fault Zone: Mapped approximately 29.5 miles west-
southwest of the site. Most recent surface rupture is of Holocene age (SCEDC,
2022).
San Jacinto Fault Zone: Mapped approximately 46.5 to 59.2 miles east-
northeast of the site, estimated to have a 31 percent probability of a M6.7 or
greater earthquake within the next 30 years (Working Group on California
Earthquake Probabilities, 2008).
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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 0.6-mile from the exposed coastline and at an
elevation of approximately 61 to 62 feet above MSL Review of the Tsunami
Inundation Map for Emergency Planning, Encinitas Quadrangle, the site is located
outside the inundation area. There is no risk of tsunami inundation at the site.
A seiche is a run-up of water within a lake or embayment triggered by fault-or
landslide-induced ground displacement. The site is located near a coastal lagoon that
is not considered capable of producing a seiche and inundating the subject site.
Flood Hazard: Review of the FEMA flood maps number 06073C0764H, effective on
12/20/2019, the project site is located within the Special Flood Hazard Area (SFHA)
X. Zone Xis described as minimal flood hazard. The civil engineer should verify this
statement with the City of Carlsbad and County of San Diego (FEMA, 2019).
Geologic Hazards Summary: No significant geologic hazards are known to exist on
the site that would prohibit the construction of the proposed medical office building
structure and associated improvements. Ground shaking from earthquakes on active
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southern California faults and active faults in northwestern Mexico is the greatest
geologic hazard at the property. Design of the proposed structure and associated
improvements in accordance with the current building codes would reduce the
potential for injury or loss of human life. Structures constructed in accordance with
current building codes may suffer significant damage but should not undergo total
collapse.
It is our opinion, based upon a review of the available maps, our research, and our
site investigation, that the proposed structure and associated improvements would
not destabilize neighboring properties or induce the settlement of adjacent structures
or right-of-way improvements if designed and constructed in accordance with our
recommendations.
In our professional opinion, no active or potentially active fault or landslide underlies
the site in the area of the proposed construction.
IX. GROUNDWATER
Groundwater was not encountered in any of our exploratory excavations. 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.
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
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appearances of groundwater may have to be dealt with on a site-specific basis.
Proper functional surface drainage should be implemented and maintained at the
property,
x. CONCLUSIONS & RECOMMENDATIONS
The following recommendations are based upon the practical field investigations
conducted by our firm, and resulting laboratory tests, in conjunction with our
knowledge and experience with similar soils in the Carlsbad area. The opinions,
conclusions, and recommendations presented in this report are contingent upon
Geotechnical Exploration, Inc. being retained to review the final plans and
specifications as they are developed and to observe the site earthwork and
installation of foundations. Accordingly, we recommend that the following paragraph
be included on the grading and foundation plans for the project.
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.
Existing fill soils extend to relatively shallow depths of 1 to 1.5 feet across much of
the lot as encountered at the explored locations. The fill soils and upper 1 to 2 feet
of paralic deposits are, in general, loose to medium dense, slightly moist to moist,
with a generally very low expansion potential. The fill soils and upper paralic deposits
are not suitable in their current condition to support the proposed new medical office
building structure and associated improvements. Removal and recompaction of all
existing fill soils and upper paralic deposits down to adequate bearing formational
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materials at an approximate depth of 2 to 3 feet will be required to support structures
and associated site improvements.
It is our opinion, based on our current understanding of the proposed construction,
that the area of study is suitable for the planned new two-story structure and
associated improvements, provided the recommendations herein are incorporated
during design and construction.
A. Preaaration of Soils for Site Develoement
1. General: Grading should conform to the guidelines presented in the 2022
California Building Code (CBC), as well as the requirements of the City of
Carlsbad.
During earthwork construction, removals and reprocessing of loose to medium
dense materials, as well as general grading procedures of the contractor,
should be observed and 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 prepared 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, they should be approved in
writing by this office.
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2. Clearing and Stripping: In areas to receive the new medical office building
structure and exterior hardscape improvements, the ground surface should be
stripped of existing vegetation within the areas of proposed new construction.
Once the required excavations have been made down to suitable soils, 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 the
Recommendations below. Prior to any filling operations, the cleared and
stripped vegetation and debris should be disposed of off-site.
3. Excavation: After the pertinent areas of the site have been cleared and
stripped, the existing fill soils or soft, loose soils in the area of the new
structure and exterior hardscape improvements should be removed and
recompacted. It ls anticipated that the depth of removal will be 2 to 3 feet
below existing grade.
Based on our exploratory excavations, unsuitable fill soils in all areas to receive
structural improvements that are proposed to bear on compacted fill soils must
be removed to expose suitable formational soils and replaced with compacted
fill soils to reach final grades.
Based on our experience with similar materials in the project area, it is our
opinion that the existing fill soils and formational 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 excavation 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
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4.
area. Undercutting may be recommended at time of grading if shallow portions
of fill removal are encountered in an area and deeper fills in another area under
the proposed structures or improvements.
The areal extent required to remove the surficial soils and existing fill 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 foundation of the new structure bearing on fHI soils and any areas
to receive exterior improvements where feasible, or to the depth of excavation
or fill at that location, whichever is greater.
Subqrade Preparation: A~er the project site area has been cleared, stripped,
and the required excavations made, the exposed approved subgrade soils in
areas to receive new fill and/or slab on-grade improvements should be
scarified to a depth of 6 inches, moisture conditioned, and compacted to the
requirements for structural fill. While not anticipated, in the event that planned
cuts expose any medium to highly expansive soil materials in the building
areas, they should be scarified and moisture conditioned to at least 5 percent
for medium and highly expansive soils (where encountered).
5. Material for Fill: Existing on-site low-expansion potential (Expansion Index of
50 or less (per ASTM D4829-19) granular 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. During
building pad preparation, and if encountered, all rock over 6 inches in diameter
should be removed from the excavated soils. In addition, imported (if
necessary) 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
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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.
The on-site, low expansive soils can be used as structural fill and as retaining
wall backfill (if proposed). Backfill material to be placed behind retaining walls
should be low expansive soils (E.I. less than 50), with rocks no larger than 3
inches in diameter.
6. Structural Fifi 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 D1557-12el. Fill material should
be spread and compacted in uniform horizontal lifts not exceeding 8 inches in
uncompacted thickness. When using lightweight compaction equipment, the
thickness of loose soils layers to be compacted shall be no more than 5 inches.
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. Low
expansive granular soils should be moisture conditioned to 3 percent above
optimum moisture content.
Soil compaction testing by nuclear method ASTM D6938-17a or sand cone
method ASTM 01556-lSel should be performed every 2 feet or less of fill
placement by a representative of Geotechnical Exploration, Inc.
Furthermore, our representative should perform necessary observation of fill
placement during grading operations throughout the project.
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Any rigid improvements founded on the existing undocumented fill soils can
be expected to undergo movement and possible damage. Geotechnlcal
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. If
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.
7. Chloride and Soluble Sulfate Testing: Large concentrations of chlorides will
adversely affect any ferrous metals such as iron and steel. Soil with a chloride
concentration greater than or equal to 500 ppm (0.05 percent) or more is
considered corrosive to ferrous metals. The chloride content of the tested soil
measured at approximately 10 ppm or 0.0010 percent, indicating that, at this
site, chloride is not a major factor in corrosion to ferrous metals. Test results
should be evaluated by an engineer specializing in soil corrosivity.
The primary cause of deterioration of concrete in foundations and other below
ground structures is the corrosive attack by soluble sulfates present in the soil
and groundwater. The results of water-soluble sulfate testing performed on a
representative sample of the near surface soils in the general area of the
proposed structure, yielded a soluble sulfate content of less than 30 ppm or
0.003 percent, indicating that the proposed cement-concrete structures that
are in contact with the underlying soils are anticipated to be affected with a
negligible sulfate exposure. Test results should be evaluated by an engineer
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8.
specializing in soil corrosivity. The most common factor in determining soils
corrosivity to ferrous metals is electrical resistivity. As soils' resistivity
decreases, its corrosivity to ferrous metals increases. The tested soil yielded
high resistivity of 18,000 Ohm-cm, indicating that the tested soils are not
corrosive to ferrous metals.
Soils and fluids are considered neutral when pH is measured at 7, acidic when
pH is measured at <7 and alkaline when measured at >7. Soils are considered
corrosive when the pH gets down to around 5.5 or less. Results of the
laboratory testing yielded a pH value of 7 .5 indicating that pH is not a
significant factor in soil corrosivity to metals.
It is noted that Geotechnical Exploration Inc., does not practice corrosion
engineering and our assessment here should be construed as an aid to the
owner or owner's representative. A corrosion specialist should be consulted
for any specific design requirement.
Trench Backfill: All utility trenches should be backfilled with properly
compacted imported fill or low expansive on-site soils, but capped (upper 8
inches) with properly compacted on-site soils. Imported 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 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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9.
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.
Observations and Testing: As stated in CBC 2022, 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 shaft
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 geotechnica/ 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 thicknesses during
placement and compaction of compacted fill prior to placement of
compacted fill, inspect subgrade and verify that site has been prepared
properly.
Section 1705.6 "Soils" statement and Table 1705.6 indicate that it is
mandatory that a representative of this firm (responsible geotechnical
engineering firm), perform observations and fill compaction testing during
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Grand Hope Medical Office Building
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Job No. 23-14312
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11. Seismic Design Criteria: The proposed structure should be designed in
accordance with the 2022 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 33.163497 degrees and a longitude
of -117.345523 degrees, utilizing a program titled "Seismic Design Map Toof"
and provided by the USGS through SEAOC, which provides a solution for ASCE
7-16 utilizing digitized files for the Spectral Acceleration maps. Refer to
Appendix C for the ASCE Seismic Summary Report.
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 D, Stiff Soils, which considers the dense soils or foundations
bearing in dense formational soils.
13. Spectral Acceleration and Design Values: The structural seismic design, when
applicable, should be based on the following seismic soil parameter values,
which are based on the site location, soil characteristics, and seismic maps by
USGS, as required by the 2022 CBC. Seismic design soil parameters were
obtained with the SEAOC Seismic Design Map Tool and they are presented in
summarized form below. A full computer printout is presented as Appendix C.
TABLE I
Mapped Spectral Acceleration Values and Design Parameters
Ss I 51 I SMs l SM1 I Sos I 501 Fa Fv PGA PGAM SDC
1.066 I 0.38611.14410.73910.76310.492 I 1.074 1.913 0.469 0.531 D
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c. Foundation Recommendations
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14. Footings: Based on our field exploration and the encountered variable density
surficial fill soils at the explored locations of the site where the proposed
structure and new foundations are planned, we recommend that the new
footings be supported on continuous spread or isolated foundations bearing on
properly compacted fill soils or dense formational soils.
No footings should be underlain by existing loose or undocumented fill soils.
All structure footings should be founded on formational soils or properly
compacted fill prepared as recommended in the above Recommendations. All
footings for the two-story structure should be founded at least 18 inches into
dense formational soils or properly compacted fill 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.
15. Bearing Values: At the recommended depths previously discussed, footings
on compacted fill or formational soils may be designed for allowable bearing
pressures of 2,500 psf for combined dead and live loads and 3,325 psf, 33
percent increase, for all loads including wind or seismic. The footings should,
however, have a minimum width of 15 inches and depth of 18 inches into
dense formation or properly compacted fill. An increase in soil allowable static
bearing can be used as follows: 1,000 psf for each additional foot over 1.5
feet in depth and 600 psf for each additional foot in width to a total static
bearing capacity not exceeding 5,000 psf. As previously indicated, all of the
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may be used in design provided the footings are poured neat against dense
soils or properly compacted fill materials. These lateral resistance values
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 from
retaining walls and from the bottom of foundation for regular building
foundations. Retaining walls supporting surcharge loads or affected by upper
foundations should consider the effect of those upper loads.
18. Settlement: Settlement under structural design loads is expected to be within
tolerable limits for the proposed structure. For footings designed in accordance
with the recommendations presented in the preceding paragraphs, we
anticipate that total settlement should be within allowable tolerance not exceed
1 inch and angular rotation should be less than 1/240.
D. Concrete Slab On-Grade Criteria
Slabs on-grade may only be used on new, properly compacted fill or when bearing
on medium dense to 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 sufficient reinforcing steel to
reduce the separation of cracks, should they occur. Slab subgrade soil should
be verified by a Geotechnlcal Exploration, Inc. representative to have the
proper moisture content within 48 hours prior to placement of the vapor barrier
and pouring of concrete.
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Grand Hope Medical Office Building
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to schedule a pre-construction meeting and to coordinate a review, in-person
or digital, of the vapor barrier installation.
22. Exterior Slab Thickness and Reinforcement: Exterior slab reinforcement and
control joints should be designed by the project Structural Engineer. As a
minimum for protection of on-site improvements, we recommend that all
exterior concrete slabs be at least 4 inches thick, reinforced with No. 3 bars at
15-inch centers, both ways at the center of the slab, and contain adequate
isolation and control joints. Control joints should be spaced no farther than 15
feet apart and at reentrant corners.
The performance of on-site improvements can be greatly affected by soil base
preparation and the quality of construction. It is therefore important that all
improvements are properly designed and constructed for the existing soil
conditions. The improvements should not be built on loose soils or fills placed
without our observation and testing. The subgrade of exterior improvements
should be verified as properly prepared within 48 hours prior to concrete
placement.
E. Retaining Wall Design Criteria
It is our understanding that no retaining walls are currently planned for the site.
However, if needed, retaining wall recommendations for walls higher than 3 feet that
retain more than 3 feet of soil are presented below.
23. Design Parameters -Unrestrained: The active earth pressure to be utilized in
the design of any cantilever site retaining walls, utilizing on-site low-expansive
[EI less than 50] or imported very low-to low-expansive soils [EI less than
SO] as backfill should be based on an Equivalent Fluid Weight of 38 pcf (for
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Grand Hope Medical Office Building
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level backfill only). For 2.0: 1.0 sloping low expansive backfill, the cantilever
site retaining walls should be designed with an equivalent fluid pressure of 52
pcf.
Unrestrained retaining walls should be backfilled with properly compacted very
low to low expansive soils. Unrestrained retaining walls should be designed
when vertical load surcharged for a conversion load factor of 0.31 to convert
vertical uniform surcharge loads to uniform horizontal lateral surcharge loads.
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 14 pcf. This seismic increment is waived for restrained retaining
walls. If the walls are designed as unrestrained walls, the seismic load should
be added to the static soil pressure.
25. Retaining Wall Drainage: The preceding design pressures assume that the
walls are backfilled wlth properly compacted low expansion potential materials
(Expansion Index less than SO) 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 ]-Drain 200/220 and J-Drain SWD, or equivalent. No
perforated pipes or gravel are required with the ]-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. Waterproofing should extend from the bottom to the top of
the wall.
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F.
Backfill placed behind retaining walls should be compacted to a minimum
degree of compaction of 90 percent using light compaction equipment. If
heavy equipment is used, the walls should be appropriately temporarily
braced. Crushed rock gravel may only be used as backfill in areas where
access is too narrow to place compacted soils. Behind shoring walls sand slurry
backfill may be used behind lagging.
Geotechnical Exploration, Inc. will assume no liability for damage to
structures or improvements that is attributable to poor drainage. The
architectural plans should clearly indicate that subdrains for any lower-level
walls be placed at an elevation at least 1 foot below the bottom of the lower-
level slabs.
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,
Temporary Slopes
Due to the limited 2-to 3-foot depths of removal and recompaction grading
operations, no significant slopes or temporary slopes should be produced during site
preparation. Perimeter property line 2-to 3-foot cuts made during grading will be
observed by geotechnical staff and site-specific recommendations given if warranted
at that ti me.
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26. Temporary Slope Observations: A representative of Geotechnical
Exploration, Inc. must observe temporary slopes during construction. In the
event that soils comprising a temporary slope are not as anticipated, any
required slope design changes would be presented at that time.
G. eavements
27. Concrete Pavement: We recommend that new driveways subject only to
automobile and light truck traffic be at least 6 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 within 48 hours prior to paving. The
concrete should conform to Section 201 of The Standard Specifications for
Public Works Construction, 2021 Edition, for Class 560-C-3250.
In order to control shrinkage cracking, we recommend that saw-cut,
weakened-plane joints be provided at about 12-foot centers both ways and at
re-entrant 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 shrinkage control joint should be one-quarter of the slab thickness and its
width should not exceed 0.02-foot. Reinforcing steel is not necessary unless
it is desired to increase the joint spacing recommended above. Control joints
should be sealed with concrete pavement sealant.
H. Site Draioaae CoositferatiPns
28. 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.
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29. Surface Drainage: Adequate measures should be taken to properly finish-
grade the lot after the structures and other improvements are in place.
Drainage waters from this site and adjacent properties should be directed away
from the footings, floor slabs, and slopes, onto the natural drainage direction
for this area or into properly designed and approved drainage facilities by the
City of Carlsbad to be indicated by the project Civil Engineer.
Roof gutters and downspouts should be installed on the structure with the
runoff directed away from the foundation 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 2 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.
30. 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
S percent within 5 feet of 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 structure or other improvements or
anywhere on the site.
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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 deaning any such
debris that may be in the street at the end of each work day or after a storm
event that causes breach in the installed construction BMPs.
All stockpiles of uncompacted soil and/or building materials that are intended
to be left unprotected for a period greater than 7 days are to be provided with
erosion and sediment controls. Such soil must be protected each day when
the probability of rain is 40% or greater. A concrete washout should be
provided on all projects that propose the construction of any concrete
improvements that are to be poured in place. All erosion/sediment control
devices should be maintained in working order at all times. All slopes that are
created or disturbed by construction activity must be protected against erosion
and sediment transport at all times. The storage of all construction materials
and equipment must be protected against any potential release of pollutants
into the environment.
XI. GRADING NOTES
Geotechnica/ Exploration, Inc. recommends that we be retained to verify the
actual soil conditions revealed during site grading work and footing excavation to be
as anticipated in this Report of Preliminary Geotechnical Investigation for the project.
In addition, the placement and compaction of any fill or backfill soils during site
grading work must be observed and tested by the soil engineer.
It is the responsibility of the grading contractor and general contractor to comply with
the requirements on the grading plans as well as the local grading ordinance. All
retaining wall and trench backfill should be properly compacted. Geotechnica/
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Grand Hope Medical Office Building
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Job No. 23-14312
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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.
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
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Grand Hope Medical Office Building
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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.
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 Geotechnlcal 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.
Ii
REFERENCES
JOB NO. 23-14312
July 2023
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.
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.
California Geological Survey, 2021a, Earthquake Zones of Required Investigation, La Jolla Quadrangle,
Earthquake Fault Zones, Official Map.
California Geological Survey, 2021b, Earthquake Zones of Required Investigation, Point Loma
Quadrangle, Earthquake Fault Zones, Official Map.
Crowell, J.C., 1962, Displacement Along the San A.ndreas, 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.
Department of Conservation, California Geological Survey, 2018, Earthquake Fault Zones A Guide for
Government Agencies, Property Owners/Developers, and Geoscience Practitioners for Assessing Fault
Rupture Hazards in California, Special Publication 42.
DeFrisco, M., 2021, The Rose Canyon Fault Zone in The Point Loma and la Jolla 7.5 Minute Quadrangles
San Diego County, California, California Geological Survey, Fault Evaluation Report 265.
Earthquake Engineering Research Institute (EERI), 2021.
Geo Tracker, 2021, https:/ /geotracker. waterboards.ca .gov/
Grant Ludwig, L.B. and Shearer, P.M., 2004, Activity of the Offshore Newport-Inglewood Rose Canyon
Fault Zone, Coastal Southern California, from Relocated Microseismicity, Bulletin of the Seismological
Society of America, 94(2), 747-752.
Greene, H.G., Bailey, K.A., Clarke, S.H., Ziony, J.I. and Kennedy, M.P., 1979, Implications of fault
patterns of the inner California continental borderland between San Pedro and San Diego, in Abbott,
P.L., and Elliot, W.J., eds., Earthquakes and other perils, San Diego region: San Diego Association of
Geologists, Geological Society of America field trip, p. 21-28.
Greensfelder, R.W., 1974, Maximum Credible Rock Accelerations from Earthquakes in California,
California Division of Mines and Geology.
Hart, E.W. and Bryant, W.A., 1997, Fault-Rupture Hazard Zones in California, California Division of Mines
and Geology, Special Publication 42.
Hart, E.W., Smith, D.P. and Saul, R.B., 1979, Summary Report: Fault Evaluation Program, 1978 Area
(Peninsular Ranges-Salton Trough Region), California Division of Mines and Geology, Open-file Report
79-10 SF, 10.
;,1
REFERENCES/Page 2
Hauksson, E. and Jones, LM., 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., et.al., 1975, Character and Recency of Faulting San Diego Metropolitan Area, California,
DMG Special Report 123.
Kennedy, M. P. and Clarke, S.H., 1999, Analysis of Late Quaternary Faulting ·in San Diego Bay and
Hazard to the Coronado Bridge, DMG Open File Report 97-lOA.
Kennedy, M.P. and Tan, S.S., 2008, Geologic Map of the San Diego 30'x60' Quadrangle, California.
California Geological Survey, Regional Geologic Map No. 3 Scale: 1:100,000.
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): el601946.
Southern California Earthquake Data Center, 2022, Earthquake information, Fault Name Index,
https : // scedc. ca ltech . ed u/ earthquake/fa u Its. html.
Toppozada, T.R. and Parke, D.L., 1982, Areas Damaged by Cal'lfornia Earthquakes, 1900-1949,
California Division of Mines and Geology, Open-file Report 82-17.
11A
L A B O R A T O R Y REPORT
Telephone {619) 425-1993 Fax 425-7917 Established 1928
CLARKSON LABORATORY AND SUPPLY INC.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Date: July 13, 2023
Purchase Order Number: Grand Hope
Sales Order Number: 60295
Account Number: GEOE.R5
To: *-------------------------------------------------*
Geotechnical Exploration Inc.
7420 Trade Street
San Diego, Ca 92121
Attention: Rector Estrella
Laboratory Number: S09700 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation: *-------------------------------------------------* One soil sample received on 07/06/23 at 11:10am,
marked as Grand Hope.
Analysis By California Test 643, 1999, Department of Transportation
Division of Construction, Method for Estimating the Service Life of
Steel Culverts.
pH 7.5
Water Added (ml)
10
5
5
5
5
Resistivity (ohm-cm)
18000
12000
10000
11000
12000
79 years to perforation for a 16 gauge metal culvert.
102 years to perforation for a 14 gauge metal culvert.
141 years to perforation for a 12 gauge metal culvert.
181 years to perforation for a 10 gauge metal culvert.
220 years to perforation for a 8 gauge metal culvert.
Water Soluble Sulfate Calif. Test 417
Water Soluble Chloride Calif. Test 422
<0.003%
0.001%
Rosa Bernal
RMB/js
Figure No. JVc
Job No. 23-14312
APPENDIX B
REGIONAL GEOLOGIC DESCRIPTION
In the Coastal Plain region, 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 Naci6n 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 forms 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 metasedimenta.ry rocks remain as roof pendants of marble, schist, slate,
quartzite and gneiss throughout the Peninsular Ranges. Locally, Miocene-age
volcanic rocks and flows have also accumulated within these mountains (e.g.,
Jacumba Valley). Regional tectonic forces and erosion over time have uplifted and
unroofed these granitic rocks to expose them at the surface (Demere, 1997).
The Salton Trough is the northerly extension of the Gulf of California. This zone is
undergoing active deformation related to faulting along the Elsinore and San Jacinto
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).
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
D
REFERENCES/Page 2
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 (CGS), an "active" fault, described by CGS (2018) as a
Holocene-Active fault, is one that has had (ground) surface displacement within
Holocene time, the last 11,700. In addition, "potentially active fault" has been
amended to Pre-Holocene fault: a fault whose recency of past movement is older
than 11,700 years, and thus does not meet the criteria of Holocene-Active fault as
defined in the State Mining and Geology Board regulations.
A three-tier fault classification is used as follows:
• Holocene-Active Faults have surface displacement within Holocene time, where
Holocene time is the geological epoch that began 11,700 years before present.
• Pre-Holocene Faults have demonstrable displacement older than Holocene time.
• Age-Undetermined Faults are faults whose age of most recent movement is not
known or is unconstrained by dating methods or by limitations in stratigraphic
resolution.
During recent history, prior to April 2010, the San Diego County area has been
relatively quiet seismically. The youngest paleoearthquake that cuts the early
historical living surface is likely the 1862 San Diego earthquake that had an estimated
magnitude of M6 (Legg and Agnew, 1979; Singleton et al., 2019). Paleoseismic
trenches at the Presidio Hills Golf Course on the main trace of the Rose Canyon Fault
contained evidence for historical ground rupturing earthquakes as recently as 1862
and the mid-1700s. Results of the study also suggest the Rose Canyon Fault has a
~700-800-year recurrence interval (Singleton et al., 2019).
On June 15, 2004, a MS.3 earthquake occurred approximately 45 miles southwest of
downtown San Diego (26 miles west of Rosarito, Mexico). Another widely felt
earthquake on a distant southern California fault was a MS.4 event that took place
on July 29, 2008, west-southwest of the Chino Hills area of Riverside County.
Several earthquakes ranging from MS.Oto M6.0 occurred in northern Baja California,
centered in the Gulf of California on August 3, 2009. A MS.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.
On April 04, 2010, a large earthquake occurred in Baja California, Mexico. It was
widely felt throughout the southwest including Phoenix, Arizona and San Diego in
California. This M7 .2 event, the Sierra El Mayor earthquake, occurred in northern
Baja California, approximately 40 miles south of the Mexico-USA border at shallow
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depth along the principal plate boundary between the North American and Pacific
plates. According to the U.S. Geological Survey this is an area with a high level of
historical seismicity, and it has recently also been seismically active, although this is
the largest event to strike in this area since 1892. The April 04, 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.
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. Ground
motions for the April 04, 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 07, 2010, a MS.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. It was followed by more than 60 aftershocks of Ml.3 and greater during
the first hour.
In the last 50 years, there have been four other earthquakes in the magnitude MS.0
range within 20 kilometers of the Coyote Creek segment: MS.8 in 1968, MS.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.
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APPENDIX D
SLAB MOISTURE INFORMATION
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 E1745-09 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.ZR-06 Guide for
Concrete Slabs that Receive Moisture-Sensitive Flooring Materials; and ACI 302.ZR-
06 Guide to Concrete Floor and Slab Construction.
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 El 745 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 E1745-09 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.
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
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(grade beam, wall, or slab) using the manufacturer's recommended accessory for
sealing the vapor retarder to pre-existing or freshly placed concrete.
Additionally, in actual practice, stakes are often driven through the retarder material,
equipment is dragged or rolled across the retarder, overlapping or jointing is not
properly implemented, etc. All these construction deficiencies reduce the retarder's
effectiveness. In no case should retarder/barrier products be punctured or gaps be
allowed to form prior to or during concrete placement. Vapor barrier-safe screeding
and forming systems should be used that will not leave puncture holes in the vapor
barrier, such as Beast Foot (by Stego Industries) or equivalent.
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.
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.
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