HomeMy WebLinkAboutTechnical Report 6 - R-8 Site GeotechnicalGEOTECHNICAL INVESTIGATION
OTAY RANCH VILLAGE 7
NEIGHBORHOOD R-8
CHULA VISTA, CALIFORNIA
PREPARED FOR
NOVEMBER 18, 2021
REVISED MAY 9, 2024
PROJECT NO. 06862-52-67
GROCON
INCORPORATED
GEOTECHNICAL • ENVIRONMENTAL MATERIALSO
6960 Flanders Drive • San Diego, California 92121-2974 • Telephone 858.558.6900 • Fax 858.558.6159
Project No. 06862-52-67
November 18, 2021
Revised May 9, 2024
Baldwin & Sons, Inc.
20 Corporate Plaza
Newport Beach, California 92660
Attention: Ms. Maria Miller
Subject: GEOTECHNICAL INVESTIGATION
OTAY RANCH VILLAGE 7
NEIGHBORHOOD R-8
CHULA VISTA, CALIFORNIA
Dear Ms. Miller:
In accordance with your request and authorization of our Proposal No. LG-19506 dated December 27,
2019, we herein submit the results of our geotechnical investigation for the subject project. We
performed our investigation to evaluate the underlying soil and geologic conditions and potential
geologic hazards, and to assist in the design of the proposed development and associated improvements.
We have revised this report to address the 3rd party comments prepared by Michael Baker International.
The accompanying report presents the results of our study and conclusions and recommendations
pertaining to geotechnical aspects of the proposed project. The site is suitable for the proposed
development and improvements provided the recommendations of this report are incorporated into the
design and construction of the planned project.
Should you have questions regarding this report, or if we may be of further service, please contact the
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
Kenneth W. Haase
CEG 2775
Shawn Foy Weedon
GE 2714
KWH:SFW:arm
(e-mail) Addressee
TABLE OF CONTENTS
1.PURPOSE AND SCOPE ................................................................................................................. 1
2.SITE AND PROJECT DESCRIPTION ........................................................................................... 2
3.PREVIOUS GRADING ................................................................................................................... 3
4.GEOLOGIC SETTING .................................................................................................................... 4
5.SOIL AND GEOLOGIC CONDITIONS ........................................................................................ 55.1 Topsoil (Unmapped) .............................................................................................................. 55.2 Previously Placed Fill (Qpf) .................................................................................................. 55.3 San Diego Formation (Unmapped) ........................................................................................ 55.4 Otay Formation (To, Tob) ..................................................................................................... 6
6.GEOLOGIC STRUCTURE ............................................................................................................. 6
7.GROUNDWATER .......................................................................................................................... 6
8.GEOLOGIC HAZARDS ................................................................................................................. 78.1 Regional Faulting and Seismicity .......................................................................................... 78.2 Ground Rupture ..................................................................................................................... 88.3 Liquefaction ........................................................................................................................... 88.4 Storm Surge, Tsunamis, and Seiches ..................................................................................... 98.5 Landslides .............................................................................................................................. 98.6 Slope Stability ........................................................................................................................ 98.7 Erosion ................................................................................................................................. 10
9.CONCLUSIONS AND RECOMMENDATIONS ......................................................................... 119.1 General ................................................................................................................................. 119.2 Excavation and Soil Characteristics .................................................................................... 129.3 Grading ................................................................................................................................ 139.4 Earthwork Grading Factors .................................................................................................. 179.5 Slope Stability Analyses ...................................................................................................... 179.6 Temporary Excavations ....................................................................................................... 189.7 Seismic Design Criteria ....................................................................................................... 199.8 Foundation and Concrete Slabs-On-Grade Recommendations ........................................... 219.9 Exterior Concrete Flatwork ................................................................................................. 279.10 Retaining Walls ................................................................................................................... 289.11 Lateral Loading .................................................................................................................... 319.12 Preliminary Pavement Recommendations ........................................................................... 329.13 Site Drainage and Moisture Protection ................................................................................ 369.14 Grading and Foundation Plan Review ................................................................................. 369.15 Testing and Observation Services During Construction ...................................................... 36
LIMITATIONS AND UNIFORMITY OF CONDITIONS
MAPS AND ILLUSTRATIONS Figure 1, Geologic Map Figure 2, Geologic Cross Sections
APPENDIX A FIELD INVESTIGATION
APPENDIX B LABORATORY TESTING
APPENDIX C SLOPE STABILITY ANALYSES
APPENDIX D RECOMMENDED GRADING SPECIFICATIONS
LIST OF REFERENCES
Geocon Project No. 06862-52-67 - 1 - November 18, 2021
Revised May 9, 2024
GEOTECHNICAL INVESTIGATION
1. PURPOSE AND SCOPE
This report presents the results of our geotechnical investigation for a new residential development at
Otay Ranch Village 7, Neighborhood R-8 in the City of Chula Vista, California as shown on the Vicinity
Map.
Vicinity Map
The purpose of the geotechnical investigation is to evaluate the surface and subsurface soil conditions
and general site geology, and to identify geotechnical constraints that may affect development of the
property including faulting, liquefaction and seismic shaking based on the 2022 CBC seismic design
criteria. In addition, we provided recommendations for remedial grading, shallow foundations, concrete
slab-on-grade, concrete flatwork, pavement and retaining walls.
We reviewed the following plans and reports in preparation of this report:
1.Final Report of Testing and Observation Services Performed During Site Grading, Otay Ranch Village 7, Neighborhood R-2, Chula Vista, California, prepared by Geocon Incorporated, dated April 12, 2006 (Project No. 06862-52-03A).
2.Geotechnical Investigation, Otay Ranch Village 7, R-2 and Village 4 Community Park, Chula Vista, California, prepared by Geocon Incorporated, dated May 5, 2004 (Project No. 06862-52-03).
3.Conceptual Site Plan, Otay Ranch Village 7 – Neighborhood R-8, City of Chula Vista, California, prepared by ARKArchitects, Inc., dated September 22, 2023.(Project No. 2022-114)
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Revised May 9, 2024
The scope of this investigation included reviewing readily available published and unpublished geologic
literature (see List of References), performing engineering analyses and preparing this report. We also
advanced 3 exploratory borings to a maximum depth of about 60 feet, sampled soil and performed
laboratory testing. Appendix A presents the exploratory boring logs and details of the field investigation.
The details of the laboratory tests and a summary of the test results are shown in Appendix B and on the
boring logs in Appendix A. The slope stability analyses are shown in Appendix C and the Recommended
Grading Specifications are shown in Appendix D.
2. SITE AND PROJECT DESCRIPTION
The property is an irregularly shaped parcel location south of the Otay Ranch Village 7 development
and a storm water drainage channel, east of La Media Road, west of a communications tower (Vortac
Site) and north of Santa Luna Street. The site slopes from an elevation of about 540 feet Mean Sea Level
(MSL) at the eastern limits to 400 feet MSL at the northwest limits. The area was previously graded
during the development of Otay Ranch Village 7 and the installation of La Media Road. The Existing
Site Plan shows the current site conditions.
Existing Site Plan
We understand the planned development will consist of a multi-family residential development with
accommodating utilities, landscaping, storm water management devices, driveways and surface parking
areas. A recreation area will be installed on the southern portion of the site near the neighborhood access
point. Cut and fill slopes are planned on the east and north/west, respectively, with heights of up to about
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Revised May 9, 2024
70 feet. The Proposed Site Plan shows the preliminary layout of the planned buildings and
improvements.
Proposed Site Plan
The locations, site descriptions, and proposed development are based on our site reconnaissance, review
of published geologic literature, field investigations, and discussions with project personnel. If
development plans differ from those described herein, Geocon Incorporated should be contacted for
review of the plans and possible revisions to this report.
3. PREVIOUS GRADING
The site is located within an area that was previously graded as part of the Otay Ranch Village 7,
Neighborhood R-2 development in 2005 and 2006. The central portion of the site is situated over a
previous shallow canyon that was filled in during grading operations. The previous grading operations
consisted of removing unsuitable materials (i.e. surficial soil and vegetation) prior to the placement of
compacted fill. We provided the testing and observation services during grading operations that
consisted of performing laboratory and compaction testing. The field density test results indicate that
the fill soil was placed at a dry density of at least 90 percent of the laboratory maximum dry density.
The results of the density tests are shown in the referenced report dated April 12, 2006. Fill within the
canyon ranges between 3 and 15 feet in depth. Due to the presence of an approximately 1-foot thick
layer of bentonite claystone, the constructed slopes were graded at inclinations of about 4:1 (horizontal
to vertical) to achieve a suitable stability rather than constructing stability fill buttress slopes at steeper
inclinations.
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4. GEOLOGIC SETTING
The site is located in the eastern portion of the coastal plain within the southern portion of the Peninsular
Ranges Geomorphic Province of southern California. The Peninsular Ranges is a geologic and
geomorphic province that extends from the Imperial Valley to the Pacific Ocean and from the Transverse
Ranges to the north and into Baja California to the south. The coastal plain of San Diego County is
underlain by a thick sequence of relatively undisturbed and non-conformable sedimentary rocks that
thicken to the west and range in age from Upper Cretaceous through the Pleistocene with intermittent
deposition. The sedimentary units are deposited on bedrock Cretaceous to Jurassic age igneous and
metavolcanic rocks. Geomorphically, the coastal plain is characterized by a series of 21, stair-stepped
marine terraces (younger to the west) that have been dissected by west flowing rivers. The coastal plain
is a relatively stable block that is dissected by relatively few faults consisting of the potentially active
La Nacion Fault Zone and the active Rose Canyon Fault Zone. The Peninsular Ranges Province is also
dissected by the Elsinore Fault Zone that is associated with and sub-parallel to the San Andreas Fault
Zone, which is the plate boundary between the Pacific and North American Plates. The site consists of
Oligocene-age (Tertiary) Otay Formation that generally consists of sandstones with interbeds of
claystones and siltstones with a reported maximum thickness of roughly 400 feet. The Otay Formation
contains multiple layers of bentonitic claystone that is highly expansive and has low shear strength. The
Regional Geologic Map shows the geologic units in the area of the site. During our investigation, we
encountered previously placed fill (Qpf) in the western and central portion of the site as shown on the .
Geologic Map, Figure 1. The following Regional Geologic Map is an excerpt from published geologic
maps and is not updated to show the current conditions.
Regional Geologic Map
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Revised May 9, 2024
5. SOIL AND GEOLOGIC CONDITIONS
We encountered two surficial soil units (consisting of topsoil and previously placed fill) and one
formational unit (consisting of the Otay Formation). The occurrence, distribution, and description of
each unit encountered is shown on the Geologic Map, Figure 1 and on the boring logs in Appendix A.
The Geologic Cross-Sections, Figure 2, show the approximate subsurface relationship between the
geologic units. We prepared the geologic cross-sections using interpolation between exploratory
excavations and observations; therefore, actual geotechnical conditions may vary from those illustrated
and should be considered approximate. The surficial soil and geologic units are described herein in order
of increasing age.
5.1 Topsoil (Unmapped)
We encountered topsoil in Boring B-2 to a depth of approximately 3½ feet. In general, topsoil is located
at the surface overlying the Otay Formation and consists of loose to medium dense, damp to moist,
clayey sand and possesses a “very low” to “medium” expansion index (expansion index of 90 or less).
We expect the thickest areas of topsoil are located within the higher portions of the site that were left as
natural ground during previous grading. The topsoil is not considered suitable in its current condition
for the support of foundations or structural fill, and remedial grading will be required.
5.2 Previously Placed Fill (Qpf)
We encountered previously placed compacted fill in Borings B-1 and B-3 ranging from about 3 to 5½
feet thick. Based on the referenced grading report, the previously placed fill at the site ranges up to 15
feet thick. In general, the fill consists of loose (near the surface) to medium dense, damp to moist, clayey
sand and stiff sandy clay and possesses a “very low” to “medium” expansion index (expansion index of
90 or less). The upper portions of the previously placed fill is not considered suitable in its current
condition for the support of foundations or structural fill and remedial grading will required. The
previously placed fill can be reused for new compacted fill during grading operations provided it is
generally free of roots and debris.
5.3 San Diego Formation (Unmapped)
Tertiary-age San Diego Formation was previously mapped in the eastern portion of the site. The San
Diego Formation rests unconformably above the Otay Formation when present and generally consists
of weakly to well-cemented cemented, micaceous, moist to wet, light gray to light yellowish brown,
brownish yellow, and strong brown, fine- to medium-grained sandstone and siltstone with zones of
cemented gravel and cobble beds. This unit was not encountered during our field investigation. If present
and or/encountered in the eastern cut slope during construction, a stability fill will likely need to be
constructed due to the relatively cohesionless nature of the unit. The San Diego Formation possesses a
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Revised May 9, 2024
“very low” to “low” expansion potential (expansion index of 50 or less). The San Diego Formation is
considered suitable for support of structural loads but may require stabilization if encountered in
proposed cut slopes.
5.4 Otay Formation (To, Tob)
Tertiary-age Otay Formation (To) is exposed across the site and located below the topsoil and previously
placed fill. This unit consists of interbeds of dense to very dense, slightly cemented, silty to clayey
sandstone and hard, siltstone and claystone layers. Excavations will generally be possible with heavy-
duty grading equipment with heavy effort; however, moderately to highly cemented zones may create
very difficult ripping and generate oversize cemented cobbles and boulders. The Otay Formation is
suitable for the support of proposed fill and structural loads.
In addition, a laterally extensive bed of bentonite claystone (Tob) with a variable thickness of
approximately 1 to 1½ feet exists at an approximate elevation of 440 to 443 feet MSL. Bentonite layers
have been mapped as underlying the majority of Otay Ranch and its occurrence is well documented in
the geologic literature (Cleveland, 1960). The bentonitic claystone beds consist of highly expansive
clays (expansion index greater than 130), which typically exhibit low shear strength. The Geologic Map,
Figure 1, shows the approximate elevation of the bentonite layer as encountered in the borings and
previous grading operations. The bentonite claystone will require slope stabilization at the locations
shown on the Geologic Map.
6. GEOLOGIC STRUCTURE
Bedding attitudes observed within formational materials encountered during the investigation are nearly
horizontal to slightly dipping toward the northwest and southwest. The regional dip of sedimentary units
in the eastern Chula Vista area is generally 1 to 5 degrees toward the southwest. The granular portions
of the formational units are typically massive with bedding not discernible. Shear zones create a
possibility for slope instability and, where encountered during grading, should be evaluated for the
necessity of remedial grading. High-angle contacts between formational units are not uncommon;
however, it is our opinion that adverse geologic structure does not present a significant geologic hazard
to the proposed development of the site if the recommendations of this report are incorporated into
design and construction.
7. GROUNDWATER
We did not encounter groundwater during our site investigation; however, we did encounter minor
seepage in Boring B-3. It is not uncommon for seepage conditions to develop where none previously
existed when sites are irrigated or infiltration is implemented. Seepage is dependent on seasonal
precipitation, irrigation, land use, among other factors, and varies as a result. Proper surface drainage
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Revised May 9, 2024
will be important to future performance of the project. We expect groundwater is deeper than about 100
feet below existing grade. We do not expect groundwater to be encountered during construction of the
proposed development.
8. GEOLOGIC HAZARDS
8.1 Regional Faulting and Seismicity
A review of the referenced geologic materials and our knowledge of the general area indicate that the
site is not underlain by active, potentially active, or inactive faults. An active fault is defined by the
California Geological Survey (CGS) as a fault showing evidence for activity within the last
11,700 years. The site is not located within a State of California Earthquake Fault Zone.
The USGS has developed a program to evaluate the approximate location of faulting in the area of
properties. The following figure shows the location of the existing faulting in the San Diego County and
Southern California region. The fault traces are shown as solid, dashed and dotted that represent well-
constrained, moderately constrained and inferred, respectively. The fault line colors represent faults with
ages less than 150 years (red), 15,000 years (orange), 130,000 years (green), 750,000 years (blue) and
1.6 million years (black).
Faults in Southern California
The San Diego County and Southern California region is seismically active. The following figure
presents the occurrence of earthquakes with a magnitude greater than 2.5 from the period of 1900
through 2015 according to the Bay Area Earthquake Alliance website.
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Revised May 9, 2024
Considerations important in seismic design include the frequency and duration of motion and the soil
conditions underlying the site. Seismic design of structures should be evaluated in accordance with the
California Building Code (CBC) guidelines currently adopted by the local agency.
Earthquakes in Southern California
8.2 Ground Rupture
Ground surface rupture occurs when movement along a fault is sufficient to cause a gap or rupture where
the upper edge of the fault zone intersects the ground surface. The potential for ground rupture is
considered to be very low due to the absence of active faults at the subject site.
8.3 Liquefaction
Liquefaction typically occurs when a site is located in a zone with seismic activity, onsite soils are
cohesionless or silt/clay with low plasticity, groundwater is encountered within 50 feet of the surface
and soil densities are less than about 70 percent of the maximum dry densities. If the four previous
criteria are met, a seismic event could result in a rapid pore water pressure increase from the earthquake-
generated ground accelerations. Due to the lack of a permanent, near-surface groundwater table and the
very dense nature of the underlying fill and Otay Formation, liquefaction potential for the site is
considered very low.
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8.4 Storm Surge, Tsunamis, and Seiches
Storm surges are large ocean waves that sweep across coastal areas when storms make landfall. Storm surges
can cause inundation, severe erosion and backwater flooding along the water front. The site is located greater
than 9 miles from the Pacific Ocean and is at an elevation of about 400 feet or greater above Mean Sea Level
(MSL). Therefore, the potential of storm surges affecting the site is considered very low.
A tsunami is a series of long period waves generated in the ocean by a sudden displacement of large
volumes of water. Causes of tsunamis include underwater earthquakes, volcanic eruptions, or offshore
slope failures. The potential for the site to be affected by a tsunami is negligible due to the distance from
the Pacific Ocean and the site elevation.
A seiche is a run-up of water within a lake or embayment triggered by fault- or landslide-induced ground
displacement. The site is not located in the vicinity of or downstream from such bodies of water.
Therefore, the risk of seiches affecting the site is negligible.
8.5 Landslides
While a bentonite claystone layer is present at the site, we did not observe evidence of previous or
incipient slope instability at the site during previous grading or this study. Published geologic mapping
indicates landslides are not present on or adjacent to the site. Therefore, we opine the potential for future
landsliding adversely affecting the proposed improvements is low provided the grading
recommendations presented herein are followed.
8.6 Slope Stability
We evaluated the maximum proposed cut and fill slope heights, as depicted on the Geologic Map, Figure
1, to evaluate both surficial and global stability based on the current geologic information. The portions
of the site planned for grading are generally underlain by Tertiary-age Otay Formation. The unit most
likely to be subject to slope instability is the bentonitic claystone layer within the Otay Formation
encountered at the site. Slope stability analyses using the two-dimensional computer program GeoStudio
2018 developed by Geo-Slope International Ltd. Are presented in Appendix C. The proposed slopes
have calculated factors of safety greater than 1.5 for global and shallow sloughing conditions provided
our recommendations for grading and drainage are incorporated into the design and construction of the
proposed slopes.
In general, permanently graded fill slopes constructed of granular soil and cut slopes excavated within
the Otay Formation at the site with gradients of 2:1 (horizontal to vertical) or flatter will possess Factors
of Safety of 1.5 or greater. However, buttress and stability fills will be required during grading
operations on the northern and western portion of the site where bentonite is located within the slope
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Revised May 9, 2024
zone (see Geologic Cross-Sections, Figure 2). The eastern slope should be buttresses due to the existing
claystones within the Otay Formation. The buttress widths will range from 15 feet to 20 feet, as
calculated. The Geologic Map and Cross-Sections provide the required width of the buttresses for the
planned development.
Grading of cut and fill slopes should be designed in accordance with the requirements of the local
building codes of the City of Chula Vista and the 2022 California Building Code (CBC). Mitigation of
unstable cut slopes can be achieved by the use of drained stability or buttress fills.
Table 8.6 presents the surficial slope stability analysis for the proposed sloping conditions.
TABLE 8.6
SURFICIAL SLOPE STABILITY EVALUATION
Parameter Value
Slope Condition Cut Slope Fill Slope
Slope Height, H ∞ ∞
Vertical Depth of Saturation, Z 3 Feet 3 Feet
Slope Inclination, I (Horizontal to Vertical) 2:1 (26.6 Degrees) 2:1 (26.6 Degrees)
Total Soil Unit Weight, γ 125 pcf 125 pcf
Water Unit Weight, γW 62.4 pcf 62.4 pcf
Friction Angle, 33 Degrees 28 Degrees
Cohesion, C 325 psf 300 psf
Factor of Safety = (C+(γ+γW )Zcos2I tan)/(γZsinI cosI) 2.8 2.5
Slopes should be landscaped with drought-tolerant vegetation having variable root depths and requiring
minimal landscape irrigation. In addition, slopes should be drained and properly maintained to reduce
erosion.
8.7 Erosion
The site is relatively gently sloping to west but is not located adjacent to the Pacific Ocean coast or a
free-flowing drainage where active erosion is occurring. The site is located south of an existing
controlled drainage area. Provided the engineering recommendations herein are followed and the project
civil engineer prepares the grading plans in accordance with generally-accepted regional standards, we
do not expect erosion to be a major impact to site development. In addition, we expect the proposed
development would not increase the potential for erosion if properly designed.
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9. CONCLUSIONS AND RECOMMENDATIONS
9.1 General
9.1.1 We did not encounter soil or geologic conditions during our exploration or previous grading
operations that would preclude the proposed development, provided the recommendations
presented herein are followed and implemented during design and construction. We will
provide supplemental recommendations if we observe variable or undesirable conditions
during construction, or if the proposed construction will differ from that anticipated herein.
9.1.2 With the exception of possible moderate to strong seismic shaking and slope instability, we
did not observe or know of significant geologic hazards to exist on the site that would
adversely affect the proposed project.
9.1.3 The topsoil, upper weathered portions of the Otay Formation, and upper portions of the
previously placed fill are potentially compressible and unsuitable in their present condition
for the support of compacted fill or settlement-sensitive improvements. Remedial grading of
these materials should be performed as discussed herein. The dense portions of the previously
placed fill and Otay Formation are considered suitable for the support of proposed fill and
structural loads.
9.1.4 The bentonite claystone layer at the site should be stabilized using designed buttresses, as
shown on the Geologic Map and Geologic Cross-Sections, Figures 1 and 2, respectively.
9.1.5 We did not encounter groundwater during our subsurface exploration and we do not expect it
to be a constraint to project development. However, seepage within surficial soils and within
the formational materials was observed during our investigation and may be encountered
during grading operations, especially during the rainy season.
9.1.6 Excavation of the topsoil, previously placed fill and the Otay Formation should generally be
possible with moderate to very heavy effort using conventional, heavy-duty equipment during
grading and trenching operations. We expect possible refusal in localized areas for
excavations into strongly cemented portions of the Otay Formation.
9.1.7 Proper drainage should be maintained in order to preserve the engineering properties of the
fill in both the building pads and slope areas. Recommendations for site drainage are provided
herein.
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9.1.8 Based on our review of the project plans, we opine the planned development can be
constructed in accordance with our recommendations provided herein. We do not expect the
planned development will destabilize or result in settlement of adjacent properties if properly
constructed.
9.1.9 Surface settlement monuments and canyon subdrains will not be required on this project.
9.2 Excavation and Soil Characteristics
9.2.1 Excavations of the in-situ soil should be possible with moderate to heavy effort using
conventional heavy-duty equipment. Excavation of the formational materials will require very
heavy effort and may generate oversized material using conventional heavy-duty equipment
during the grading operations. Oversized rock (rocks greater than 12-inches in maximum
dimension) generated during excavation of The Otay Formation can be incorporated within
deep compacted fill areas, if available.
9.2.2 The soil encountered during previous grading operations is considered to be non-expansive”
and “expansive” (expansion index [EI] of 20 or less and greater than 20, respectively) as
defined by 2022 California Building Code (CBC) Section 1803.5.3. We expect a majority of
the soil encountered possess a “very low” to “medium” expansion potential (EI of 90 or less)
in accordance with ASTM D 4829. The bentonitic claystone possesses a “high” to “very high”
expansion potential (EI greater than 90) in accordance with ASTM D 4829. Table 9.2 presents
soil classifications based on the expansion index.
TABLE 9.2
EXPANSION CLASSIFICATION BASED ON EXPANSION INDEX
Expansion Index (EI) ASTM D 4829 Expansion
Classification
2022 CBC Expansion
Classification
0 – 20 Very Low Non-Expansive
21 – 50 Low
Expansive 51 – 90 Medium
91 – 130 High
Greater Than 130 Very High
9.2.3 Laboratory tests performed during previous grading operations indicate the on-site materials
at the locations tested possess “S0” sulfate exposure to concrete structures as defined by 2022
CBC Section 1904 and ACI 318-19 Chapter 19. The presence of water-soluble sulfates is not
a visually discernible characteristic; therefore, other soil samples from the site could yield
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different concentrations. Additionally, over time landscaping activities (i.e., addition of
fertilizers and other soil nutrients) may affect the concentration.
9.2.4 Geocon Incorporated does not practice in the field of corrosion engineering. Therefore, further
evaluation by a corrosion engineer may be performed if improvements susceptible to
corrosion are planned.
9.3 Grading
9.3.1 Grading should be performed in accordance with the recommendations provided in this report,
the Recommended Grading Specifications contained in Appendix D and the City of Chula
Vista’s Grading Ordinance. Geocon Incorporated should observe the grading operations on a
full-time basis and provide testing during the fill placement.
9.3.2 Prior to commencing grading, a preconstruction conference should be held at the site with the
regulatory agency, developer, grading/underground contractors, civil engineer and
geotechnical engineer in attendance. Special soil handling and/or the grading plans can be
discussed at that time.
9.3.3 Site preparation should begin with the removal of deleterious material, debris and vegetation.
The depth of vegetation removal should be such that material exposed in cut areas or soil to
be used as fill is relatively free of organic matter. Material generated during stripping and/or
site demolition should be exported from the site. Asphalt and concrete should not be mixed
with the fill soil unless approved by the Geotechnical Engineer.
9.3.4 Topsoil, the upper portions of the formational materials, and the upper 2 to 3 feet of the
previously placed fill within the limits of grading should be removed to expose firm,
competent material. The actual depth of removal should be evaluated in the field during
grading operations.
9.3.5 We do not expect to observe bentonitic claystone near the proposed finish pad grade
elevations for the proposed development. Bentonitic claystone layers that occur within 5 feet
of finish grade, if observed, should be removed and replaced with properly compacted fill that
possesses a “very low” to “medium” expansion potential (EI of 90 or less). The undercut
within the building pads should be sloped at least 2 percent toward the adjacent street or deep
fill area.
9.3.6 Bentonitic claystone layers encountered during the normal excavation or undercutting of
building pads, streets, or slopes should be mixed with granular materials in a ratio of at least
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two parts sand to one part bentonite clay and compacted to a dry density of at least 90 percent
of the laboratory maximum dry density at or slightly above optimum moisture. The mixed
bentonite clay should be placed at least 5 feet below finish grade, at least 15 feet from the face
of a fill slope, and not within buttress or stability fill slopes.
9.3.7 The upper 3 feet of cut and cut/fill transition lots should be over excavated and replaced with
properly compacted fill due to the very dense and cemented nature of the formational
materials. The bottom of the excavations should be sloped at least one percent toward the
adjacent deeper fill areas or adjacent roadways to reduce the potential for subsurface water to
saturate fill materials.
9.3.8 The City of Chula Vista requires additional removals and grading requirements within the
street and right-of-way areas. Based on the City of Chula Vista, the upper 5 feet of fill and
upper 3 feet of formational materials within the public right of way areas should possess an
expansion index of 90 or less. Additional removals of formational materials may be required
if the expansion index is greater than 90.
9.3.9 We should observe the grading operations and the removal bottoms to check the exposure of
the formational materials prior to the placement of compacted fill. Deeper excavations may
be required if highly weathered formational materials are present at the base of the removals.
Table 9.3.1 provides a summary of the grading recommendations.
TABLE 9.3.1
SUMMARY OF GRADING RECOMMENDATIONS
Area Removal Requirements
Site Development
Remove to Competent Formational Materials or
Competent Previously Placed Fill
Undercut 3 Feet Below Finish Grade Cut or
Cut/Fill Transitions
Street and Right-Of-Way Upper 5 Feet of Fill/3 Feet of Formation
Expansion Index of 90 or Less
Exposed Bottoms of Remedial Grading Scarify Upper 12 Inches
Slope 1 Percent to Adjacent Street or Deepest Fill
9.3.10 Some areas of overly wet and saturated soil could be encountered due to the existing landscape
and pavement areas. The saturated soil would require additional effort prior to placement of
compacted fill or additional improvements. Stabilization of the soil would include scarifying
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and air-drying, removing and replacement with drier soil, use of stabilization fabric (e.g.
Tensar TX7 or other approved fabric), or chemical treating (i.e. cement or lime treatment).
9.3.11 Slope stability analysis utilizing drained direct shear strength parameters based on our
experience with similar soil types in nearby areas and laboratory test results indicates that the
proposed fill slopes, constructed of on-site materials, should have calculated factors of safety
of at least 1.5 under static conditions for both deep-seated failure and shallow sloughing
conditions. Cut slopes that are not impacted by bentonitic clay layers were also found to
possess a calculated factor of safety in excess of 1.5 for a deep-seated failure condition.
However, some of the proposed slopes will require buttressing to obtain a factor of safety of
at least 1.5. These slopes are shown on the Geologic Map (Figure 1) and should be graded
with buttresses varying from approximately 15 to 20 feet wide. The design buttress widths
are shown on the Geologic Map.
9.3.12 Due to the expansive and blocky nature of the Otay Formation, we recommend that a stability
fill is constructed along the face of the descending cut slope on the east side of the site.
9.3.13 The Typical Buttress and Stability Fill Detail should be used for design and construction of
slope buttresses, where required. The backcut for the buttress should commence at least 10
feet from the top of the proposed finish-graded slope and should extend at least 3 feet below
adjacent pad grade or below the bentonite layer. The base of the key should be slopes at least
5 percent to the drain, into slope. Stability fills may also be required on cut slopes that expose
the San Diego Formation where cohesionless sand is encountered.
Typical Buttress and Stability Fill Detail
9.3.14 The slope backcut should be a 1:1 and in accordance with OSHA requirements. Chimney drains
should be installed along the backcut that are 4 feet wide, 20-foot on center and provide dual-sided
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drainage. Closer spacing may be required where seepage is encountered. The collector pipe at the
base of the backcut should consists of a minimum 4-inch diameter, perforated, Schedule 40 PVC
pipe drained at a minimum of 1 percent. The pipe should be surrounded by ¾-inch gravel wrapped
in an approved filter fabric (Mirafi 140N or equivalent).
9.3.15 Cut slope excavations including buttresses and shear keys should be observed during grading
operations to check that soil and geologic conditions do not differ significantly from those
expected. During the construction of buttresses, there is a risk that the temporary backcut
slopes will become unstable. This risk can be reduced by grading the buttress fill in short
segments and/or flattening the inclination of the temporary slope.
9.3.16 The site should then be brought to final subgrade elevations with fill compacted in layers. In
general, soil native to the site is suitable for use from a geotechnical engineering standpoint
as fill if relatively free from vegetation, debris and other deleterious material. Layers of fill
should be about 6 to 8 inches in loose thickness and no thicker than will allow for adequate
bonding and compaction. Fill, including backfill and scarified ground surfaces, should be
compacted to a dry density of at least 90 percent of the laboratory maximum dry density near
to slightly above optimum moisture content in accordance with ASTM Test Procedure
D 1557. Fill materials placed below optimum moisture content may require additional
moisture conditioning prior to placing additional fill. The upper 12 inches of subgrade soil
underlying vehicular pavement should be compacted to a dry density of at least 95 percent of
the laboratory maximum dry density near to slightly above optimum moisture content shortly
before paving operations.
9.3.17 Import fill (if necessary) should consist of the characteristics presented in Table 9.3.2. Geocon
Incorporated should be notified of the import soil source and should perform laboratory
testing of import soil prior to its arrival at the site to determine its suitability as fill material.
TABLE 9.3.2
SUMMARY OF IMPORT FILL RECOMMENDATIONS
Soil Characteristic Values
Expansion Potential “Very Low” to “Medium” (Expansion Index of 90 or less)
Particle Size Maximum Dimension Less Than 3 Inches
Generally Free of Debris
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9.4 Earthwork Grading Factors
9.4.1 Estimates of shrink-swell factors are based on comparing laboratory compaction tests with
the density of the material in its natural state and experience with similar soil types. Variations
in natural soil density and compacted fill render shrinkage value estimates very approximate.
As an example, the contractor can compact fill to a density of 90 percent or higher of the
laboratory maximum dry density. Thus, the contractor has at least a 10 percent range of
control over the fill volume. Based on the work performed to date in the Otay Ranch area and
considering the discussion herein, the earthwork factors in Table 9.4 may be used as a general
basis for estimating how much the on-site soils may shrink or swell when removed from their
natural state and placed as compacted fill.
TABLE 9.4
SHRINKAGE AND BULK FACTORS
Soil Unit Shrink/Bulk Factor
Topsoil (unmapped) 10% to 15% Shrink
Previously Placed Fill (Qpf) 2% Shrink to 1% Bulk
Otay Formation (To) 4% to 8% Bulk
9.5 Slope Stability Analyses
9.5.1 We performed slope stability analyses using the two-dimensional computer program
GeoStudio created by Geo-Slope International Ltd. We calculated the factor of safety for the
planned slopes for rotational-mode and block-mode analyses using the Spencer’s method.
Output of the computer program including the calculated factor of safety and the failure
surface is presented in Appendix C.
9.5.2 We used average drained direct shear strength parameters based on laboratory tests and our
experience with similar soil types in nearby areas for the slope stability analyses. Our calculations
indicate the proposed slopes, constructed of on-site materials, should have calculated factors of
safety (FOS) of at least 1.5 under static conditions, for both deep-seated failure and shallow
sloughing conditions when the recommendations of this report are followed.
9.5.3 We selected Cross-Sections A-A’, B-B’, C-C’ and D-D’ to perform the slope stability
analyses. Appendix C presents the results of the slope stability analyses.
9.5.4 Among the slopes analyzed for acceptable calculated factors of safety, Cross-Sections A-A’
and C-C’ will require buttresses due to the presence of bentonite claystone layers. Buttress
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designs have assumed a 1:1 (horizontal to vertical) frontcut and backcut extending down
through the critical bentonite claystone layers.
9.5.5 Due to the very light loads expected from the planned homes and improvements, the loads are
considered negligible with no appreciable impact to the slope stability analyses and, therefore
were not incorporated into the analyses.
9.5.6 Planned buttress keys and proposed subdrains should be surveyed during construction with their
approximate locations depicted on the Geologic Map using the 40-scale grading plans (Figure 1).
The buttresses will require the construction of a subdrain located at the heel of the buttress (toe of
the backcut) and should be as-built and surveyed by the project civil engineer.
9.5.7 Excavations including buttresses, shear keys, and stability fills should be observed during
grading by an engineering geologist with Geocon to evaluate whether soil and geologic
conditions do not differ significantly from those expected or identified in this report.
9.5.8 We performed the slope stability analyses based on the interpretation of geologic conditions
encountered during our field investigation. We should evaluate the geologic conditions during
the grading operations to check if the conditions observed during grading are consistent with
our interpretations. Additional slope stability analyses and modifications to the proposed
buttresses may be required during the grading operations.
9.5.9 The buttress excavations are not planned adjacent to existing improvements or residences. If
excavation failures were to occur, the failures would be limited to within the property limits
and outside improvements/structures would not be affected. In addition, the grading
contractor would be required to remove the volume of soil that failed and evaluate the
additional excavation procedures.
9.5.10 Slopes should be landscaped with drought-tolerant vegetation having variable root depths and
requiring minimal landscape irrigation. In addition, slopes should be drained and properly
maintained to reduce erosion.
9.6 Temporary Excavations
9.6.1 The recommendations included herein are provided for stable excavations. It is the
responsibility of the contractor and their competent person to ensure all excavations,
temporary slopes and trenches are properly constructed and maintained in accordance with
applicable OSHA guidelines in order to maintain safety and the stability of the excavations
and adjacent improvements. These excavations should not be allowed to become saturated or
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Revised May 9, 2024
to dry out. Surcharge loads should not be permitted to a distance equal to the height of the
excavation from the top of the excavation. The top of the excavation should be a minimum of
15 feet from the edge of existing improvements. Excavations steeper than those recommended
or closer than 15 feet from an existing surface improvement should be stored in accordance
with applicable OSHA codes and regulations.
9.6.2 The stability of the excavations is dependent on the design and construction of the shoring
system and site conditions. Therefore, Geocon Incorporated cannot be responsible for site
safety and the stability of the proposed excavations.
9.7 Seismic Design Criteria
9.7.1 Table 9.7.1 summarizes site-specific design criteria obtained from the 2022 California
Building Code (CBC; Based on the 2021 International Building Code [IBC] and ASCE 7-16),
Chapter 16 Structural Design, Section 1613 Earthquake Loads. We used the computer
program U.S. Seismic Design Maps, provided by the Structural Engineers Association (SEA)
to calculate the seismic design parameters. The short spectral response uses a period of 0.2
second. We evaluated the Site Class based on the discussion in Section 1613.2.2 of the 2022
CBC and Table 20.3-1 of ASCE 7-16. The buildings and improvements should be designed
using a Site Class C where the fill thickness is 20 feet or less or a Site Class D where the fill
is thicker than 20 feet. The values presented herein are for the risk-targeted maximum
considered earthquake (MCER). Sites designated as Site Class D, E and F may require
additional analyses if requested by the project structural engineer and client.
TABLE 9.7.1
2022 CBC SEISMIC DESIGN PARAMETERS
Parameter Value 2022 CBC Reference
Site Class C D Section 1613.2.2
Fill Thickness, T (feet) T<20 T>20 --
MCER Ground Motion Spectral Response
Acceleration – Class B (short), SS 0.766g 0.766g Figure 1613.2.1(1)
MCER Ground Motion Spectral Response
Acceleration – Class B (1 sec), S1 0.278g 0.278g Figure 1613.2.1(2)
Site Coefficient, FA 1.200 1.200 Table 1613.2.3(1)
Site Coefficient, FV 1.500* 2.044* Table 1613.2.3(2)
Site Class Modified MCER Spectral Response
Acceleration (short), SMS 0.920g 1.920g Section 1613.2.3 (Eqn
16-36)
Site Class Modified MCER Spectral Response
Acceleration – (1 sec), SM1 0.417g* 0.568g* Section 1613.2.3 (Eqn
16-37)
5% Damped Design
Spectral Response Acceleration (short), SDS 0.613g 0.613g Section 1613.2.4 (Eqn
16-38)
5% Damped Design
Spectral Response Acceleration (1 sec), SD1 0.278g* 0.379g* Section 1613.2.4 (Eqn
16-39)
*See following paragraph..
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9.7.2 Using the code-based values presented in the previous table, in lieu of performing a ground
motion hazard analysis, requires the exceptions outlined in ASCE 7-16 Section 11.4.8 be
followed by the project structural engineer. Per Section 11.4.8 of ASCE/SEI 7-16, a ground
motion hazard analysis should be performed for projects for Site Class “D” sites with S1
greater than 0.2g. Section 11.4.8 also provides exceptions which indicate that the ground
motion hazard analysis may be waived provided the exceptions are followed. Supplement 3
of ASCE 7-16 provides an exception stating that that the GMHA may be waived provided
that the parameter SM1 is increased by 50% for all applications of SM1. The values for
parameters SM1 and SD1 presented herein above have not been increased in accordance with
Supplement 3 of ASCE 7-16.
9.7.3 Table 9.7.2 presents the mapped maximum considered geometric mean (MCEG) seismic
design parameters for projects located in Seismic Design Categories of D through F in
accordance with ASCE 7-16.
TABLE 9.7.2
2022 CBC SITE ACCELERATION DESIGN PARAMETERS
Parameter Value ASCE 7-16
Site Class C D --
Fill Thickness, T (Feet) T<20 T>20 --
Mapped MCEG
Peak Ground Acceleration, PGA 0.333g 0.333g Figure 22-9
Site Coefficient, FPGA 1.200 1.267 Table 11.8-1
Site Class Modified MCEG
Peak Ground Acceleration, PGAM
0.400g 0.422g Section 11.8.3 (Eqn 11.8-1)
9.7.4 Conformance to the criteria in Tables 9.7.1 and 9.7.2 for seismic design does not constitute
any kind of guarantee or assurance that significant structural damage or ground failure will
not occur in the event of a large earthquake. The primary goal of seismic design is to protect
life, not to avoid all damage, since such design may be economically prohibitive.
9.7.5 The project structural engineer and architect should evaluate the appropriate Risk Category
and Seismic Design Category for the planned structures. The values presented herein assume
a Risk Category of II and resulting in a Seismic Design Category D. Table 9.7.3 presents a
summary of the risk categories in accordance with ASCE 7-16.
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TABLE 9.7.3
ASCE 7-16 RISK CATEGORIES
Risk
Category Building Use Examples
I Low risk to Human Life at Failure Barn, Storage Shelter
II
Nominal Risk to Human Life at
Failure (Buildings Not Designated as
I, III or IV)
Residential, Commercial and Industrial
Buildings
III Substantial Risk to Human Life at
Failure
Theaters, Lecture Halls, Dining Halls,
Schools, Prisons, Small Healthcare
Facilities, Infrastructure Plants, Storage
for Explosives/Toxins
IV Essential Facilities
Hazardous Material Facilities,
Hospitals, Fire and Rescue, Emergency
Shelters, Police Stations, Power
Stations, Aviation Control Facilities,
National Defense, Water Storage
9.8 Foundation and Concrete Slabs-On-Grade Recommendations
9.8.1 The foundation recommendations herein are for proposed residential structures. The
foundation recommendations have been separated into three categories based on either the
maximum and differential fill thickness or expansion index. The foundation category criteria
are presented in Table 9.8.1. We will provide final foundation categories for each building or
lot after finish pad grades have been achieved and we perform laboratory testing of the
subgrade soil.
TABLE 9.8.1
FOUNDATION CATEGORY CRITERIA
Foundation
Category
Maximum Fill
Thickness, T (Feet)
Differential Fill
Thickness, D (Feet) Expansion Index (EI)
I T<20 -- EI<50
II 20<T<50 10<D<20 50<EI<90
III T>50 D>20 90<EI<130
9.8.2 Table 9.8.2 presents minimum foundation and interior concrete slab design criteria for
conventional foundation systems.
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TABLE 9.8.2
CONVENTIONAL FOUNDATION RECOMMENDATIONS BY CATEGORY
Foundation
Category
Minimum Footing
Embedment
Depth, D (inches)
Minimum Continuous
Footing
Reinforcement
Minimum Footing
Width (Inches)
I 12 Two No. 4 bars, one top
and one bottom
12 – Continuous, WC
24 – Isolated, WI
II 18 Four No. 4 bars, two top
and two bottom
III 24 Four No. 5 bars, two top
and two bottom
9.8.3 The foundations should be embedded in accordance with the recommendations herein and the
Wall/Column Footing Dimension Detail. The embedment depths should be measured from
the lowest adjacent pad grade for both interior and exterior footings. Footings should be
deepened such that the bottom outside edge of the footing is at least 7 feet horizontally from
the face of the slope (unless designed with a post-tensioned foundation system as discussed
herein).
Wall/Column Footing Dimension Detail
9.8.4 The proposed structures can be supported on a shallow foundation system founded in the
compacted fill/formational materials. Table 9.8.3 provides a summary of the foundation
design recommendations.
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TABLE 9.8.3
SUMMARY OF FOUNDATION RECOMMENDATIONS
Parameter Value
Allowable Bearing Capacity 2,000 psf
Estimated Total Settlement: Foundation Loads 1 Inch
Estimated Differential Settlement: Foundation Loads ½ Inch in 40 Feet
9.8.5 The bearing capacity values presented herein are for dead plus live loads and may be increased
by one-third when considering transient loads due to wind or seismic forces.
9.8.6 The concrete slab-on-grades should be a designed in accordance with Table 9.8.4.
TABLE 9.8.4
CONVENTIONAL SLAB-ON-GRADE RECOMMENDATIONS BY CATEGORY
Foundation
Category
Minimum Concrete
Slab Thickness
(inches)
Interior Slab
Reinforcement
Typical Slab
Underlayment
I 4 6 x 6 – 10/10 welded wire
mesh at slab mid-point
3 to 4 Inches of
Sand/Gravel/Base II 4 No. 3 bars at 24 inches on
center, both directions
III 5 No. 3 bars at 18 inches on
center, both directions
9.8.7 Slabs that may receive moisture-sensitive floor coverings or may be used to store moisture-
sensitive materials should be underlain by a vapor retarder. The vapor retarder design should be
consistent with the guidelines presented in the American Concrete Institute’s (ACI) Guide for
Concrete Slabs that Receive Moisture-Sensitive Flooring Materials (ACI 302.2R-06). The
vapor retarder used should be specified by the project architect or developer based on the type
of floor covering that will be installed and if the structure will possess a humidity controlled
environment.
9.8.8 The bedding sand thickness should be determined by the project foundation engineer,
architect, and/or developer. However, we should be contacted to provide recommendations if
the bedding sand is thicker than 6 inches. It is common to see 3 inches and 4 inches of sand
below the concrete slab-on-grade for 5-inch and 4-inch thick slabs, respectively, in the
southern California area. The foundation design engineer should provide appropriate concrete
mix design criteria and curing measures to assure proper curing of the slab by reducing the
potential for rapid moisture loss and subsequent cracking and/or slab curl. We suggest that
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the foundation design engineer present the concrete mix design and proper curing methods on
the foundation plans. It is critical that the foundation contractor understands and follows the
recommendations presented on the foundation plans.
9.8.9 As an alternative to the conventional foundation recommendations, consideration should be
given to the use of post-tensioned concrete slab and foundation systems for the support of the
proposed structures. The post-tensioned systems (foundation dimensions and embedment
depths, slab thickness and steel placement) should be designed by a structural engineer
experienced in post-tensioned slab design and design criteria of the Post-Tensioning Institute
(PTI) DC 10.5-12 Standard Requirements for Design and Analysis of Shallow Post-Tensioned
Concrete Foundations on Expansive Soils or WRI/CRSI Design of Slab-on-Ground
Foundations, as required by the 2022 California Building Code (CBC Section 1808.6.2).
Although this procedure was developed for expansive soil conditions, it can also be used to
reduce the potential for foundation distress due to differential fill settlement. The post-
tensioned design should incorporate the geotechnical parameters presented in Table 9.8.3 for
the particular Foundation Category designated. The parameters presented in Table 9.8.5 are
based on the guidelines presented in the PTI DC 10.5 design manual.
TABLE 9.8.5
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PTI) DC10.5 Design
Parameters
Foundation Category
I II III
Thornthwaite Index -20 -20 -20
Equilibrium Suction 3.9 3.9 3.9
Edge Lift Moisture Variation Distance, eM (Feet) 5.3 5.1 4.9
Edge Lift, yM (Inches) 0.61 1.10 1.58
Center Lift Moisture Variation Distance, eM (Feet) 9.0 9.0 9.0
Center Lift, yM (Inches) 0.30 0.47 0.66
9.8.10 The foundations for the post-tensioned slabs should be embedded in accordance with the
recommendations of the structural engineer. If a post-tensioned mat foundation system is
planned, the slab should possess a thickened edge with a minimum width of 12 inches and
extend below the clean sand or crushed rock layer.
9.8.11 If the structural engineer proposes a post-tensioned foundation design method other than PTI,
DC 10.5:
The deflection criteria presented in Table 9.8.5 are still applicable.
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Interior stiffener beams should be used for Foundation Categories II and III.
The width of the perimeter foundations should be at least 12 inches.
The perimeter footing embedment depths should be at least 12 inches, 18 inches and
24 inches for foundation categories I, II, and III, respectively. The embedment depths
should be measured from the lowest adjacent pad grade.
9.8.12 Our experience indicates post-tensioned slabs may be susceptible to excessive edge lift from
tensioning, regardless of the underlying soil conditions. Placing reinforcing steel at the bottom
of the perimeter footings and the interior stiffener beams may mitigate this potential. The
structural engineer should design the foundation system to reduce the potential of edge lift
occurring for the proposed structures.
9.8.13 During the construction of the post-tension foundation system, the concrete should be placed
monolithically. Under no circumstances should cold joints form between the footings/grade
beams and the slab during the construction of the post-tension foundation system unless
designed by the structural engineer.
9.8.14 Isolated footings outside of the slab area, if present, should have the minimum embedment
depth and width recommended for conventional foundations for a particular Foundation
Category. The use of isolated footings, which are located beyond the perimeter of the building
and support structural elements connected to the building, are not recommended for Category
III. Where this condition cannot be avoided, the isolated footings should be connected to the
building foundation system with grade beams in both directions. In addition, consideration
should be given to connecting patio slabs, which exceed 5 feet in width, to the building
foundation to reduce the potential for future separation to occur.
9.8.15 Interior stiffening beams should be incorporated into the design of the foundation system in
accordance with the PTI design procedures.
9.8.16 Special subgrade presaturation is not deemed necessary prior to placing concrete; however,
the exposed foundation and slab subgrade soil should be moisture conditioned, as necessary,
to maintain a moist condition as would be expected in any such concrete placement.
9.8.17 Where buildings or other improvements are planned near the top of a slope 3:1 (horizontal to
vertical) or steeper, special foundation and/or design considerations are recommended due to
the tendency for lateral soil movement to occur.
For fill slopes less than 20 feet high or cut slopes regardless of height, footings should
be deepened such that the bottom outside edge of the footing is at least 7 feet
horizontally from the face of the slope.
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When located next to a descending 3:1 (horizontal to vertical) fill slope or steeper,
the foundations should be extended to a depth where the minimum horizontal distance
is equal to H/3 (where H equals the vertical distance from the top of the fill slope to
the base of the fill soil) with a minimum of 7 feet but need not exceed 40 feet. The
horizontal distance is measured from the outer, deepest edge of the footing to the face
of the slope. A post-tensioned slab and foundation system or mat foundation system
can be used to reduce the potential for distress in the structures associated with strain
softening and lateral fill extension. Specific design parameters or recommendations
for either of these alternatives can be provided once the building location and fill
slope geometry have been determined.
If swimming pools are planned, Geocon Incorporated should be contacted for a
review of specific site conditions.
Swimming pools located within 7 feet of the top of cut or fill slopes are not
recommended. Where such a condition cannot be avoided, the portion of the
swimming pool wall within 7 feet of the slope face be designed assuming that the
adjacent soil provides no lateral support. This recommendation applies to fill
slopes up to 30 feet in height and cut slopes regardless of height. For swimming pools
located near the top of fill slopes greater than 30 feet in height, additional recom-
mendations may be required and Geocon Incorporated should be contacted for a
review of specific site conditions.
Although other improvements, which are relatively rigid or brittle, such as concrete
flatwork or masonry walls, may experience some distress if located near the top of a
slope, it is generally not economical to mitigate this potential. It may be possible,
however, to incorporate design measures which would permit some lateral soil
movement without causing extensive distress. Geocon Incorporated should be
consulted for specific recommendations.
9.8.18 The recommendations of this report are intended to reduce the potential for cracking of slabs
and foundations due to expansive soil (if present), differential settlement of fill soil with
varying thicknesses. However, even with the incorporation of the recommendations presented
herein, foundations, stucco walls, and slabs-on-grade placed on such conditions may still
exhibit some cracking due to soil movement and/or shrinkage. The occurrence of concrete
shrinkage cracks is independent of the supporting soil characteristics. Their occurrence may
be reduced by limiting the slump of the concrete, proper concrete placement and curing, and
by the placement of crack control joints at periodic intervals, in particular, where re-entrant
slab corners occur.
9.8.19 Concrete slabs should be provided with adequate crack-control joints, construction joints
and/or expansion joints to reduce unsightly shrinkage cracking. The design of joints should
consider criteria of the American Concrete Institute when establishing crack-control spacing.
Additional steel reinforcing, concrete admixtures and/or closer crack control joint spacing
should be considered where concrete-exposed finished floors are planned.
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9.8.20 Geocon Incorporated should be consulted to provide additional design parameters as required
by the structural engineer.
9.8.21 We should observe the foundation excavations prior to the placement of reinforcing steel to
check that the exposed soil conditions are similar to those expected and that they have been
extended to the appropriate bearing strata. If unexpected soil conditions are encountered,
foundation modifications may be required.
9.9 Exterior Concrete Flatwork
9.9.1 Exterior concrete flatwork not subject to vehicular traffic should be constructed in accordance
with the recommendations presented in Table 9.9. The recommended steel reinforcement
would help reduce the potential for cracking.
TABLE 9.9
MINIMUM CONCRETE FLATWORK RECOMMENDATIONS
Expansion
Index, EI Minimum Steel Reinforcement* Options Minimum
Thickness
EI < 90 6x6-W2.9/W2.9 (6x6-6/6) welded wire mesh 4 Inches No. 3 Bars 18 inches on center, Both Directions
*In excess of 8 feet square.
9.9.2 The subgrade soil should be properly moisturized and compacted prior to the placement of
steel and concrete. The subgrade soil should be compacted to a dry density of at least 90
percent of the laboratory maximum dry density near to slightly above optimum moisture
content in accordance with ASTM D 1557.
9.9.3 Even with the incorporation of the recommendations of this report, the exterior concrete
flatwork has a potential to experience some uplift due to expansive soil beneath grade. The
steel reinforcement should overlap continuously in flatwork to reduce the potential for vertical
offsets within flatwork. Additionally, flatwork should be structurally connected to the curbs,
where possible, to reduce the potential for offsets between the curbs and the flatwork.
9.9.4 Concrete flatwork should be provided with crack control joints to reduce and/or control
shrinkage cracking. Crack control spacing should be determined by the project structural
engineer based upon the slab thickness and intended usage. Criteria of the American Concrete
Institute (ACI) should be taken into consideration when establishing crack control spacing.
Subgrade soil for exterior slabs not subjected to vehicle loads should be compacted in
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Revised May 9, 2024
accordance with criteria presented in the grading section prior to concrete placement.
Subgrade soil should be properly compacted and the moisture content of subgrade soil should
be verified prior to placing concrete. Base materials will not be required below concrete
improvements.
9.9.5 Where exterior flatwork abuts the structure at entrant or exit points, the exterior slab should
be dowelled into the structure’s foundation stemwall. This recommendation is intended to
reduce the potential for differential elevations that could result from differential settlement or
minor heave of the flatwork. Dowelling details should be designed by the project structural
engineer.
9.9.6 The recommendations presented herein are intended to reduce the potential for cracking of
exterior slabs as a result of differential movement. However, even with the incorporation of
the recommendations presented herein, slabs-on-grade will still crack. The occurrence of
concrete shrinkage cracks is independent of the soil supporting characteristics. Their
occurrence may be reduced and/or controlled by limiting the slump of the concrete, the use of
crack control joints and proper concrete placement and curing. Crack control joints should be
spaced at intervals no greater than 12 feet. Literature provided by the Portland Concrete
Association (PCA) and American Concrete Institute (ACI) present recommendations for
proper concrete mix, construction, and curing practices, and should be incorporated into
project construction.
9.10 Retaining Walls
9.10.1 Retaining walls should be designed using the values presented in Table 9.10.1. Soil with an
expansion index (EI) of greater than 90 should not be used as backfill material behind
retaining walls.
TABLE 9.10.1
RETAINING WALL DESIGN RECOMMENDATIONS
Parameter Value
Active Soil Pressure, A (Fluid Density, Level Backfill) 40 pcf
Active Soil Pressure, A (Fluid Density, 2:1 Sloping Backfill) 55 pcf
Seismic Pressure, S 12H psf
At-Rest/Restrained Walls Additional Uniform Pressure (0 to 8 Feet High) 7H psf
At-Rest/Restrained Walls Additional Uniform Pressure (8+ Feet High) 13H psf
Expected Expansion Index for the Subject Property EI<90
H equals the height of the retaining portion of the wall
Geocon Project No. 06862-52-67 - 29 - November 18, 2021
Revised May 9, 2024
9.10.2 The project retaining walls should be designed as shown in the Retaining Wall Loading
Diagram.
Retaining Wall Loading Diagram
9.10.3 Unrestrained walls are those that are allowed to rotate more than 0.001H (where H equals the
height of the retaining portion of the wall) at the top of the wall. Where walls are restrained from
movement at the top (at-rest condition), an additional uniform pressure should be applied to the
wall. For retaining walls subject to vehicular loads within a horizontal distance equal to two-thirds
the wall height, a surcharge equivalent to 2 feet of fill soil should be added.
9.10.4 The structural engineer should determine the Seismic Design Category for the project in
accordance with Section 1613.3.5 of the 2022 CBC or Section 11.6 of ASCE 7-10. For
structures assigned to Seismic Design Category of D, E, or F, retaining walls that support
more than 6 feet of backfill should be designed with seismic lateral pressure in accordance
with Section 1803.5.12 of the 2022 CBC. The seismic load is dependent on the retained height
where H is the height of the wall, in feet, and the calculated loads result in pounds per square
foot (psf) exerted at the base of the wall and zero at the top of the wall.
9.10.5 Retaining walls should be designed to ensure stability against overturning sliding, and
excessive foundation pressure. Where a keyway is extended below the wall base with the
intent to engage passive pressure and enhance sliding stability, it is not necessary to consider
active pressure on the keyway.
Geocon Project No. 06862-52-67 - 30 - November 18, 2021
Revised May 9, 2024
9.10.6 Drainage openings through the base of the wall (weep holes) should not be used where the seepage
could be a nuisance or otherwise adversely affect the property adjacent to the base of the wall. The
recommendations herein assume a properly compacted granular (EI of 90 or less) free-draining
backfill material with no hydrostatic forces or imposed surcharge load. The retaining wall should
be properly drained as shown in the Typical Retaining Wall Drainage Detail. If conditions
different than those described are expected, or if specific drainage details are desired, Geocon
Incorporated should be contacted for additional recommendations.
Typical Retaining Wall Drainage Detail
9.10.7 The retaining walls may be designed using either the active and restrained (at-rest) loading
condition or the active and seismic loading condition as suggested by the structural engineer.
Typically, it appears the design of the restrained condition for retaining wall loading may be
adequate for the seismic design of the retaining walls. However, the active earth pressure
combined with the seismic design load should be reviewed and also considered in the design
of the retaining walls.
9.10.8 In general, wall foundations should be designed in accordance with Table 9.10.2. The proximity
of the foundation to the top of a slope steeper than 3:1 could impact the allowable soil bearing
pressure. Therefore, retaining wall foundations should be deepened such that the bottom outside
edge of the footing is at least 7 feet horizontally from the face of the slope.
TABLE 9.10.2
SUMMARY OF RETAINING WALL FOUNDATION RECOMMENDATIONS
Parameter Value
Minimum Retaining Wall Foundation Width 12 inches
Minimum Retaining Wall Foundation Depth 12 Inches
Minimum Steel Reinforcement Per Structural Engineer
Allowable Bearing Capacity 2,000 psf
Estimated Total Settlement 1 Inch
Estimated Differential Settlement ½ Inch in 40 Feet
Geocon Project No. 06862-52-67 - 31 - November 18, 2021
Revised May 9, 2024
9.10.9 The recommendations presented herein are generally applicable to the design of rigid concrete
or masonry retaining walls. In the event that other types of walls (such as mechanically
stabilized earth [MSE] walls, soil nail walls, or soldier pile walls) are planned, Geocon
Incorporated should be consulted for additional recommendations.
9.10.10 It is common to see retaining walls constructed in the areas of the elevator pits. The retaining
walls should be properly drained and designed in accordance with the recommendations
presented herein. If the elevator pit walls are not drained, the walls should be designed with an
increased active pressure with an equivalent fluid density of 90 pcf. It is also common to see
seepage and water collection within the elevator pit. The pit should be designed and properly
waterproofed to prevent seepage and water migration into the elevator pit.
9.10.11 Unrestrained walls will move laterally when backfilled and loading is applied. The amount of
lateral deflection is dependent on the wall height, the type of soil used for backfill, and loads
acting on the wall. The retaining walls and improvements above the retaining walls should be
designed to incorporate an appropriate amount of lateral deflection as determined by the
structural engineer.
9.10.12 Soil contemplated for use as retaining wall backfill, including import materials, should be
identified in the field prior to backfill. At that time, Geocon Incorporated should obtain samples
for laboratory testing to evaluate its suitability. Modified lateral earth pressures may be necessary
if the backfill soil does not meet the required expansion index or shear strength. City or regional
standard wall designs, if used, are based on a specific active lateral earth pressure and/or soil
friction angle. In this regard, on-site soil to be used as backfill may or may not meet the values for
standard wall designs. Geocon Incorporated should be consulted to assess the suitability of the on-
site soil for use as wall backfill if standard wall designs will be used.
9.11 Lateral Loading
9.11.1 Table 9.11 should be used to help design the proposed structures and improvements to resist
lateral loads for the design of footings or shear keys. The allowable passive pressure assumes
a horizontal surface extending at least 5 feet, or three times the surface generating the passive
pressure, whichever is greater. The upper 12 inches of material in areas not protected by floor
slabs or pavement should not be included in design for passive resistance.
Geocon Project No. 06862-52-67 - 32 - November 18, 2021
Revised May 9, 2024
TABLE 9.11
SUMMARY OF LATERAL LOAD DESIGN RECOMMENDATIONS
Parameter Value
Passive Pressure Fluid Density 350 pcf
Coefficient of Friction (Concrete and Soil) 0.35
Coefficient of Friction (Along Vapor Barrier) 0.2 to 0.25*
*Per manufacturer’s recommendations.
9.11.2 The passive and frictional resistant loads can be combined for design purposes. The lateral
passive pressures may be increased by one-third when considering transient loads due to wind
or seismic forces.
9.12 Preliminary Pavement Recommendations
9.12.1 We calculated the flexible pavement sections in general conformance with the Caltrans
Method of Flexible Pavement Design (Highway Design Manual, Section 608.4) using an
estimated Traffic Index (TI) of 5.0, 5.5, 6.0, and 7.0 for parking stalls, driveways, medium
truck traffic areas, and heavy truck traffic areas, respectively. The project civil engineer and
owner should review the pavement designations to determine appropriate locations for
pavement thickness. The final pavement sections for the parking lot should be based on the
R-Value of the subgrade soil encountered at final subgrade elevation. We have assumed an
R-Value of 10 (based on our experience in the area) and 78 for the subgrade soil and base
materials, respectively, for the purposes of this preliminary analysis. Table 9.12.1 presents the
preliminary flexible pavement sections.
TABLE 9.12.1
PRELIMINARY FLEXIBLE PAVEMENT SECTION
Location
Assumed
Traffic
Index
Assumed
Subgrade
R-Value
Asphalt
Concrete
(inches)
Class 2
Aggregate
Base (inches)
Parking stalls for automobiles
and light-duty vehicles 5.0 10 3 9
Driveways for automobiles
and light-duty vehicles 5.5 10 3 11
Medium truck traffic areas 6.0 10 3.5 12
Driveways for heavy truck traffic 7.0 10 4 15
9.12.2 Prior to placing base materials, the upper 12 inches of the subgrade soil should be scarified,
moisture conditioned as necessary, and recompacted to a dry density of at least 95 percent of
the laboratory maximum dry density near to slightly above optimum moisture content as
Geocon Project No. 06862-52-67 - 33 - November 18, 2021
Revised May 9, 2024
determined by ASTM D 1557. Similarly, the base material should be compacted to a dry
density of at least 95 percent of the laboratory maximum dry density near to slightly above
optimum moisture content. Asphalt concrete should be compacted to a density of at least 95
percent of the laboratory Hveem density in accordance with ASTM D 2726.
9.12.3 Base materials should conform to Section 26-1.028 of the Standard Specifications for The
State of California Department of Transportation (Caltrans) with a ¾-inch maximum size
aggregate. The asphalt concrete should conform to Section 203-6 of the Standard
Specifications for Public Works Construction (Greenbook).
9.12.4 The base thickness can be reduced if a reinforcement geogrid is used during the installation
of the pavement. Geocon should be contact for additional recommendations, if required.
9.12.5 A rigid Portland cement concrete (PCC) pavement section should be placed in roadway aprons
and cross gutters. We calculated the rigid pavement section in general conformance with the
procedure recommended by the American Concrete Institute report ACI 330-21 Commercial
Concrete Parking Lots and Site Paving Design and Construction – Guide. Table 9.12.2 provides
the traffic categories and design parameters used for the calculations for 20-year design life.
TABLE 9.12.2
TRAFFIC CATEGORIES
Traffic
Category Description Reliability
(%)
Slabs Cracked at End
of Design Life (%)
A Car Parking Areas and Access Lanes 60 15
B Entrance and Truck Service Lanes 60 15
E Garbage or Fire Truck Lane 75 15
9.12.6 We used the parameters presented in Table 9.12.3 to calculate the pavement design sections.
We should be contacted to provide updated design sections, if necessary.
TABLE 9.12.3
RIGID PAVEMENT DESIGN PARAMETERS
Design Parameter Design Value
Modulus of subgrade reaction, k 100 pci
Modulus of rupture for concrete, MR 500 psi
Concrete Compressive Strength 3,000 psi
Concrete Modulus of Elasticity, E 3,150,000
Geocon Project No. 06862-52-67 - 34 - November 18, 2021
Revised May 9, 2024
9.12.7 Based on the criteria presented herein, the PCC pavement sections should have a minimum
thickness as presented in Table 9.12.4.
TABLE 9.12.4
RIGID VEHICULAR PAVEMENT RECOMMENDATIONS
Traffic Category Trucks Per Day Portland Cement
Concrete, T (Inches)
A = Car Parking Areas and Access Lanes 10 5½
B = Entrance and Truck Service Lanes 10 6
50 6½
E = Garbage or Fire Truck Lanes 5 6½
10 7
9.12.8 The PCC vehicular pavement should be placed over subgrade soil that is compacted to a dry
density of at least 95 percent of the laboratory maximum dry density near to slightly above
optimum moisture content. Base materials will not be required below concrete improvements.
9.12.9 Adequate joint spacing should be incorporated into the design and construction of the rigid
pavement in accordance with Table 9.12.5.
TABLE 9.12.5
MAXIMUM JOINT SPACING
Pavement Thickness, T (Inches) Maximum Joint Spacing (Feet)
4<T<5 10
5<T<6 12.5
6<T 15
9.12.10 The rigid pavement should also be designed and constructed incorporating the parameters
presented in Table 9.12.6.
Geocon Project No. 06862-52-67 - 35 - November 18, 2021
Revised May 9, 2024
TABLE 9.12.6
ADDITIONAL RIGID PAVEMENT RECOMMENDATIONS
Subject Value
Thickened Edge
1.2 Times Slab Thickness Adjacent to Structures
1.5 Times Slab Thickness Adjacent to Soil
Minimum Increase of 2 Inches
4 Feet Wide
Crack Control Joint
Depth
Early Entry Sawn = T/6 to T/5, 1.25 Inch Minimum
Conventional (Tooled or Conventional Sawing) = T/4 to T/3
Crack Control Joint
Width
¼-Inch for Sealed Joints and Per Sealer Manufacturer’s
Recommendations
1/16- to 1/4-Inch is Common for Unsealed Joints
9.12.11 Reinforcing steel will not be necessary within the concrete for geotechnical purposes with the
possible exception of dowels at construction joints as discussed herein.
9.12.12 To control the location and spread of concrete shrinkage cracks, crack-control joints
(weakened plane joints) should be included in the design of the concrete pavement slab.
Crack-control joints should be sealed with an appropriate sealant to prevent the migration of
water through the control joint to the subgrade materials. The depth of the crack-control joints
should be in accordance with the referenced ACI guide.
9.12.13 To provide load transfer between adjacent pavement slab sections, a butt-type construction
joint should be constructed. The butt-type joint should be thickened by at least 20 percent at
the edge and taper back at least 4 feet from the face of the slab.
9.12.14 Concrete curb/gutter should be placed on soil subgrade compacted to a dry density of at least
90 percent of the laboratory maximum dry density near to slightly above optimum moisture
content. Cross-gutters that receives vehicular should be placed on subgrade soil compacted to
a dry density of at least 95 percent of the laboratory maximum dry density near to slightly
above optimum moisture content. Base materials should not be placed below the curb/gutter,
or cross-gutters so water is not able to migrate from the adjacent parkways to the pavement
sections. Where flatwork is located directly adjacent to the curb/gutter, the concrete flatwork
should be structurally connected to the curbs to help reduce the potential for offsets between
the curbs and the flatwork.
Geocon Project No. 06862-52-67 - 36 - November 18, 2021
Revised May 9, 2024
9.13 Site Drainage and Moisture Protection
9.13.1 Adequate site drainage is critical to reduce the potential for differential soil movement,
erosion and subsurface seepage. Under no circumstances should water be allowed to pond
adjacent to footings. The site should be graded and maintained such that surface drainage is
directed away from structures in accordance with 2022 CBC 1804.4 or other applicable
standards. In addition, surface drainage should be directed away from the top of slopes into
swales or other controlled drainage devices. Roof and pavement drainage should be directed
into conduits that carry runoff away from the proposed structure.
9.13.2 In the case of basement walls or building walls retaining landscaping areas, a water-proofing
system should be used on the wall and joints, and a Miradrain drainage panel (or similar)
should be placed over the waterproofing. The project architect or civil engineer should
provide detailed specifications on the plans for all waterproofing and drainage.
9.13.3 Underground utilities should be leak free. Utility and irrigation lines should be checked
periodically for leaks, and detected leaks should be repaired promptly. Detrimental soil
movement could occur if water is allowed to infiltrate the soil for prolonged periods of time.
9.13.4 Landscaping planters adjacent to paved areas are not recommended due to the potential for
surface or irrigation water to infiltrate the pavement’s subgrade and base course. Area drains
to collect excess irrigation water and transmit it to drainage structures or impervious above-
grade planter boxes can be used. In addition, where landscaping is planned adjacent to the
pavement, construction of a cutoff wall along the edge of the pavement that extends at least 6
inches below the bottom of the base material should be considered.
9.13.5 We should prepare a storm water infiltration feasibility report of storm water management
devices are planned.
9.14 Grading and Foundation Plan Review
9.14.1 Geocon Incorporated should review the grading and building foundation plans for the project
prior to final design submittal to evaluate if additional analyses and/or recommendations are
required.
9.15 Testing and Observation Services During Construction
9.15.1 Geocon Incorporated should provide geotechnical testing and observation services during
the grading operations, foundation construction, utility installation, retaining wall backfill
Geocon Project No. 06862-52-67 - 37 - November 18, 2021
Revised May 9, 2024
and pavement installation. Table 9.15 presents the typical geotechnical observations we
would expect for the proposed improvements.
TABLE 9.15
EXPECTED GEOTECHNICAL TESTING AND OBSERVATION SERVICES
Construction Phase Observations Expected Time Frame
Grading
Base of Removal Part Time
Geologic Logging Part Time to Full Time
Fill Placement and Soil Compaction Full Time
Buttress Construction Full Time
Foundations Foundation Excavation Observations Part Time to Full Time
Utility Backfill Fill Placement and Soil Compaction Part Time to Full Time
Retaining Wall Backfill Fill Placement and Soil Compaction Part Time to Full Time
Subgrade for Sidewalks,
Curb/Gutter and Pavement Soil Compaction Part Time
Pavement Construction
Base Placement and Compaction Part Time
Asphalt Concrete Placement and
Compaction Full Time
Geocon Project No. 06862-52-67 November 18, 2021
Revised May 9, 2024
LIMITATIONS AND UNIFORMITY OF CONDITIONS
1. The firm that performed the geotechnical investigation for the project should be retained to
provide testing and observation services during construction to provide continuity of
geotechnical interpretation and to check that the recommendations presented for geotechnical
aspects of site development are incorporated during site grading, construction of improvements,
and excavation of foundations. If another geotechnical firm is selected to perform the testing
and observation services during construction operations, that firm should prepare a letter
indicating their intent to assume the responsibilities of project geotechnical engineer of record.
A copy of the letter should be provided to the regulatory agency for their records. In addition,
that firm should provide revised recommendations concerning the geotechnical aspects of the
proposed development, or a written acknowledgement of their concurrence with the
recommendations presented in our report. They should also perform additional analyses deemed
necessary to assume the role of Geotechnical Engineer of Record.
2. The recommendations of this report pertain only to the site investigated and are based upon the
assumption that the soil conditions do not deviate from those disclosed in the investigation. If
any variations or undesirable conditions are encountered during construction, or if the proposed
construction will differ from that anticipated herein, Geocon Incorporated should be notified so
that supplemental recommendations can be given. The evaluation or identification of the
potential presence of hazardous or corrosive materials was not part of the scope of services
provided by Geocon Incorporated.
3. This report is issued with the understanding that it is the responsibility of the owner or his
representative to ensure that the information and recommendations contained herein are brought
to the attention of the architect and engineer for the project and incorporated into the plans, and
the necessary steps are taken to see that the contractor and subcontractors carry out such
recommendations in the field.
4. The findings of this report are valid as of the present date. However, changes in the conditions
of a property can occur with the passage of time, whether they be due to natural processes or
the works of man on this or adjacent properties. In addition, changes in applicable or appropriate
standards may occur, whether they result from legislation or the broadening of knowledge.
Accordingly, the findings of this report may be invalidated wholly or partially by changes
outside our control. Therefore, this report is subject to review and should not be relied upon
after a period of three years.
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APPROXIMATE
SITE LIMITS
·
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························································
W=15'
W=20'
FITNESS
CLU
B
H
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U
S
E
POOL
AREA
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 - 2974
PHONE 858 558-6900 - FAX 858 558-6159 SHEET OF
PROJECT NO.
SCALE DATE
FIGURE
Plotted:05/08/2024 2:37PM | By:JONATHAN WILKINS | File Location:Y:\PROJECTS\06862-52-67 Otay Ranch Village 7 - Vortex\SHEETS\06862-52-67 GeologicMAP.dwg
GEOTECHNICAL ENVIRONMENTAL MATERIALS
1" =
GEOLOGIC 1AP
OTAY RANCH VILLAGE 7 - SOUTH
CHULA VISTA, CALIFORNIA
50'05 - 09 - 2024
06862 - 52 - 67
1 1 1
B-3
GEOCON LEGEND
........PREVIOUSLY PLACED FILL (2005-2006)Qpf
........APPROX. LOCATION OF GEOTECHNICAL BORING
........APPROX. SURFACE EXPOSURE OF BENTONITE CLAYSTONE BED
........APPROX. LOCATION OF GEOLOGIC CONTACT
........APPROX. LOCATION OF GEOLOGIC CROSS-SECTION
D D'
........APPROX. ELEVATION AT BASE OF FILL (In Feet, MSL)540
........ALLUVIUM (Dotted Where Buried)Qal
........OTAY FORMATION (Dotted Where Buried)To
........APPROX. AREA OF BURIED BENTONITE CLAYSTONE BED
........APPROX. WIDTH OF BUTTRESS (In Feet)
........APPROX. LOCATION OF PROPOSED BUTTRESS
W=20'
........APPROX. LOCATION OF PROPOSED STABILITY FILL
EL
E
V
A
T
I
O
N
(
M
S
L
)
EL
E
V
A
T
I
O
N
(
M
S
L
)
DISTANCE (FEET)
SCALE: 1" = 50' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION A-A'
350
400
450
500
550
350
400
450
500
550
0 50 100 150 200 250 300 350
EL
E
V
A
T
I
O
N
(
M
S
L
)
EL
E
V
A
T
I
O
N
(
M
S
L
)
DISTANCE (FEET)
SCALE: 1" = 50' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION B-B'
300
350
400
450
500
550
300
350
400
450
500
550
0 50 100 150 200 250 300 350 400 450
EL
E
V
A
T
I
O
N
(
M
S
L
)
EL
E
V
A
T
I
O
N
(
M
S
L
)
DISTANCE (FEET)
SCALE: 1" = 50' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION D-D'
400
450
500
550
600
400
450
500
550
600
0 50 100 150 200 250 300
EL
E
V
A
T
I
O
N
(
M
S
L
)
EL
E
V
A
T
I
O
N
(
M
S
L
)
DISTANCE (FEET)
SCALE: 1" = 50' (Vert. = Horiz.)
GEOLOGIC CROSS-SECTION C-C'
350
400
450
500
550
350
400
450
500
550
0 50 100 150 200 250 290
A A'
B B'
C DC'D'
EXISTING GRADE
EXISTING GRADE
EXISTING GRADE
PROPOSED GRADE
···········································································
To
To
To
SITE
LIMITS
N87E
·······················································
SITE
LIMITS
PROPOSED GRADE
To
To
To
PROPOSED
PVT. DRIVE D
AND PARKING
STALLS
N22W
·······································································
SITE
LIMITS
To
To
To
N3W
PROPOSED GRADE
LA MEDIA RD
EXISTING GRADE
··················································
SITE
LIMITSTo
To To
PROPOSED GRADE
W=20'
PROPOSED BUTTRESS
W=15'PROPOSED BUTTRESS
PROPOSED PVT. DRIVE C
AND PARKING STALLS
PROPOSED
BLDG. 8
FG=472.4
PROPOSED
BLDG. 9
FG=471.1
PROPOSED BLDG. 7
FG=472.3
PROPOSED 8'
CMU WALL
PROPOSED BLDG. 3
FG=466.3
PROPOSED
PVT. DRIVE A
APPROXIMATE
STABILITY FILL
PROPOSED
PVT. DRIVE A
PROPOSED
BLDG. 1
FG=463.6
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 - 2974
PHONE 858 558-6900 - FAX 858 558-6159 SHEET OF
PROJECT NO.
SCALE DATE
FIGURE
Plotted:05/09/2024 7:42AM | By:JONATHAN WILKINS | File Location:Y:\PROJECTS\06862-52-67 Otay Ranch Village 7 - Vortex\SHEETS\06862-52-67 Geologic Cross-Section.dwg
GEOTECHNICAL ENVIRONMENTAL MATERIALS
1" =
GEOLOGIC CROSS - SEC8IONS
OTAY RANCH VILLAGE 7 - SOUTH
CHULA VISTA, CALIFORNIA
50'05 - 09 - 2024
06862 - 52 - 67
1 1 2
GEOCON LEGEND
........OTAY FORMATIONTo
........APPROX. ELEVATION OF BENTONITE CLAYSTONE
APPENDIX A
Geocon Project No. 06862-52-67 November 18, 2021
Revised May 9, 2024
APPENDIX A
FIELD INVESTIGATION
We performed the drilling operations on October 7 and 8, 2021 with Dave’s Drilling using an EZ Bore
120 drill rig equipped with a 30-inch diameter bucket-auger. Borings extended to maximum depth of
approximately 60 feet. The locations of the current exploratory borings are shown on the Geologic Map,
Figure 1. The boring logs are presented in this Appendix. We located the borings in the field using a
measuring tape and existing reference points; therefore, actual boring locations may deviate slightly.
We obtained samples during our subsurface exploration in the borings using a California sampler that
is composed of steel and is driven to obtain ring samples. The California sampler has an inside diameter
of 2.5 inches and an outside diameter of 3 inches. Up to 18 rings are placed inside the sampler that is
2.4 inches in diameter and 1 inch in height. We obtained ring samples at appropriate intervals, placed
them in moisture-tight containers, and transported them to the laboratory for testing. The type of sample
is noted on the exploratory boring logs.
The large-diameter boring sampler was driven up to 12 inches into the bottom of the excavation with
the use of a telescoping Kelly bar. The weight of the Kelly bar (4,500 pounds maximum) drives the
sampler and varies in weight and depth. The height of drop is usually 18 inches. Blow counts are
recorded for every 12 inches the sampler is driven. The penetration resistance values shown on the
boring logs are shown in terms of blow per foot. These values are not be taken as N-values and
adjustments have not been applied. We obtained ring samples at appropriate intervals, placed them in
moisture-tight containers, and transported them to the laboratory for testing.
We visually examined, classified, and logged the soil encountered in the borings in general accordance
with American Society for Testing and Materials (ASTM) practice for Description and Identification of
Soils (Visual-Manual Procedure D 2488). The logs depict the soil and geologic conditions observed and
the depth at which samples were obtained.
PREVIOUSLY PLACED FILL (Qpf)
Loose to medium dense, damp to moist, Clayey, fine to medium SAND
Stiff, moist, dark brown, fine to medium, Sandy CLAY
OTAY FORMATION (To)
Hard, moist, light olive to light gray, Sandy SILTSTONE; micaceous, weakly
cemented
-Less olive
-Becomes moderately cemented
Hard, moist, olive brown, Sandy CLAYSTONE
Very dense, moist, light olive gray, Silty, fine- grained SANDSTONE;
moderately cemented, massive
Hard, moist, olive brown, fine- grained, Sandy CLAYSTONE
Very dense, moist, olive, Silty, fine- to medium- grained SANDSTONE;
massive, moderately cemented
-Becomes light gray, finer grained, weakly cemented
SC
CL
ML
CL
SM
CL
SM
104.2
114.6
19.6
15.2
B1-1
B1-2
6
7
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
0
2
4
6
8
10
12
14
16
18
20
22
24
Figure A-1,
Log of Boring B 1, Page 1 of 3
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 1
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-07-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)486'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
-Becomes coarse grained
Hard, moist, olive, Sandy CLAYSTONE; abrupt contact with unit above,
N55E, 2°NW
Very dense, moist, light gray, Silty, fine- grained SANDSTONE; poorly
cemented, micaceous
Hard, moist, olive, CLAYSTONE
43.4 feet to 45 feet: BENTONITE CLAYSTONE; gray to white to pink,
blocky, intact. Layer is continuous around hole; N60E at 3°NW
Very dense, moist, olive brown, Clayey, fine- to medium- grained
SANDSTONE; very well cemented; massive
CL
SM
CL
CH
SC
116.2
117.7
119.9
14.7
12.1
12.8
B1-3
B1-4
B1-5
B1-6
B1-7
15
15
15/6"
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
26
28
30
32
34
36
38
40
42
44
46
48
Figure A-1,
Log of Boring B 1, Page 2 of 3
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 1
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-07-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)486'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
-Becomes coarser grained
BOTTOM OF HOLE AT 60 FEET
No groundwater or seepage encountered
No caving
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
50
52
54
56
58
60
Figure A-1,
Log of Boring B 1, Page 3 of 3
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 1
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-07-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)486'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
TOPSOIL
Loose to medium dense, damp to moist, dark brown, Clayey, fine to medium
SAND; little roots
OTAY FORMATION (To)
Very dense, damp, light gray, Sandy SILTSTONE; highly weathered
Hard, moist, olive to reddish brown CLAYSTONE
Very dense, moist, olive brown, Silty, fine- grained SANDSTONE;
interbedded thin claystone layers, moderately cemented
-Becomes light grayish brown, well cemented
Hard, moist, olive, Sandy CLAYSTONE
Very dense, moist, light gray, Silty, fine- grained SANDSTONE; well
cemented; massive
SC
ML
CL
SM
CL
SM
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
0
2
4
6
8
10
12
14
16
18
20
22
24
Figure A-2,
Log of Boring B 2, Page 1 of 2
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 2
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-07-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)512'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
Hard, moist, brown, CLAYSTONE
Very dense, moist, light olive to light gray, Silty, fine- grained SANDSTONE
BOTTOM OF HOLE AT 35 FEET
No groundwater or seepage encountered
No caving
CL
SM
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
26
28
30
32
34
Figure A-2,
Log of Boring B 2, Page 2 of 2
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 2
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-07-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)512'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
PREVIOUSLY PLACED FILL (Qpf)
Loose, damp, brown, Sandy CLAY, trace of organics
OTAY FORMATION (To)
Dense, damp to moist, light gray, Silty, fine- to medium- grained
SANDSTONE; friable, moderately cemented, massive
Stiff, moist, brown, Sandy CLAYSTONE; highly fractured (bedding at N47E
at 4°NW)
Dense, moist, light gray, Clayey, fine- to medium- grained SANDSTONE;
moderately cemented
-Becomes coarser grained
-Becomes olive gray
21.2 feet to 22.3 feet: BENTONITE CLAYSTONE; gray to white to pink,
blocky, fractured, waxy. Layer is continuous around hole; N70E at 4°NW
Dense, moist, olive gray, Clayey, fine- to coarse- grained SANDSTONE; trace
gravel, moderately cemented, massive
CL
SM
CL
SC
CH
SC
117.6
111.0
107.9
10.8
17.7
19.0
B3-1
B3-2
B3-3
B3-4
B3-5
6
10
10
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
0
2
4
6
8
10
12
14
16
18
20
22
24
Figure A-3,
Log of Boring B 3, Page 1 of 3
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 3
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-08-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)461'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
-Becomes very dense, difficult drilling
-Becomes very coarse grained, gravelly
-Minor seepage
-Becomes finer grained
-Minor seepage
124.1
128.2
129.6
10.2
7.7
9.0
B3-6
B3-7
B3-8
12
30/6"
30/6"
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
26
28
30
32
34
36
38
40
42
44
46
48
Figure A-3,
Log of Boring B 3, Page 2 of 3
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 3
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-08-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)461'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
-No recovery
-Difficult drilling
BORING TERMINATED AT 55 FEET
No groundwater encountered. Minor seepage encountered at 39 and 47 feet
No caving
B3-9 30/2"
... DISTURBED OR BAG SAMPLE
GEOCON
DEPTH
IN
FEET
50
52
54
Figure A-3,
Log of Boring B 3, Page 3 of 3
DR
Y
D
E
N
S
I
T
Y
(P
.
C
.
F
.
)
... DRIVE SAMPLE (UNDISTURBED)
EZ-BORE W/ 30" BUCKET AUGER PE
N
E
T
R
A
T
I
O
N
RE
S
I
S
T
A
N
C
E
(B
L
O
W
S
/
F
T
.
)
BORING B 3
... CHUNK SAMPLE
DATE COMPLETED
... SAMPLING UNSUCCESSFUL
SOIL
CLASS
(USCS)
GR
O
U
N
D
W
A
T
E
R
K. HAASE CO
N
T
E
N
T
(
%
)
SAMPLE
NO.10-08-2021
SAMPLE SYMBOLS
MO
I
S
T
U
R
E
BY:EQUIPMENT
ELEV. (MSL.)461'
06862-52-67.GPJ
MATERIAL DESCRIPTION
LI
T
H
O
L
O
G
Y
... STANDARD PENETRATION TEST
... WATER TABLE OR ... SEEPAGE
NOTE:
PROJECT NO.
THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED.
IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.
06862-52-67
APPENDIX B
Geocon Project No. 06862-52-67 November 18, 2021
Revised May 9, 2024
APPENDIX B
LABORATORY TESTING
We performed laboratory tests in accordance with generally accepted test methods of the American Society
for Testing and Materials (ASTM) or other suggested procedures. We tested selected soil samples for in-
place dry density/moisture content, plasticity index, unconfined compressive strength, gradation and
residual shear strength. The results of our current laboratory tests are presented herein. The in-place dry
density and moisture content of the samples tested are presented on the boring logs in Appendix A.
SUMMARY OF LABORATORY UNCONFINED COMPRESSIVE STRENGTH TEST RESULTS
ASTM D 1558
Sample No. Depth (feet) Geologic Unit
Hand Penetrometer Reading/Unconfined
Compression Strength (tsf) and Undrained Shear
Strength (ksf)
B1-1 10 To 4.5+
B1-2 20 To 4.5+
B1-3 30 To 4.5+
B1-4 40 To 4.5+
B1-7 44 To 4.5+
B3-1 10 To 4.5+
B3-2 15 To 4.5+
B3-4 20 To 4.5+
B3-6 25 To 4.5+
B3-7 30 To 4.5+
B3-8 40 To 4.5+
PREVIOUS GRADING LABORATORY TEST RESULTS
SUMMARY OF LABORATORY MAXIMUM DRY DENSITY
AND OPTIMUM MOISTURE CONTENT TEST RESULTS
ASTM D 1557
Sample
No. Description
Maximum
Dry Density
(pcf)
Optimum
Moisture Content
(% dry wt.)
3 Grayish brown, fine to medium, Sandy SILT 106.9 18.9
10 Light olive brown, fine, Sandy CLAY 112.2 15.8
15 Light brown, Silty SAND 115.2 14.3
Tob
D10 (mm) D30 (mm) D60 (mm)
--0.00282 0.01598
GEOLOGIC UNIT:
21'
B3-5
SAMPLE DEPTH (FT.):
SAMPLE NO.:
SIEVE ANALYSES - ASTM D 135 & D 422
OTAY RANCH VILLAGE 7, R-8
PROJECT NO.:
Cc
--
Cu
--
06862-52-67
SOIL DESCRIPTION
CLAY
TEST DATA
U.S. STANDARD SIEVE SIZE
3"2"1½
"
1 ¾"½"⅜"
#4 #8
#1
0
#1
6
#2
0
#3
0
#4
0
#5
0
#6
0
#8
0
#1
0
0
#2
0
0
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.1110100
PE
R
C
E
N
T
P
A
S
S
I
N
G
PARTICLE SIZE (mm)
SILT OR CLAY
GRAVEL SAND
COARSEFINECOARSE MEDIUM FINE
SAMPLE
NO.
GEOLOGIC
UNIT
LIQUID
LIMIT
PLASTIC
LIMIT
PLASTICITY
INDEX SOIL TYPE
B3-5 Tob @ 21' 82 37 45 CH
#NUM! #DIV/0! #NUM! #NUM!
#NUM! #DIV/0! #NUM! #NUM!
#NUM! #DIV/0! #NUM! #NUM!
#NUM! #DIV/0! #NUM! #NUM!
PLASTICITY INDEX - ASTM D 4318
OTAY RANCH VILLAGE 7, R-8
PROJECT NO.: 06862-52-67
TEST RESULTS
SOIL TYPE DESCRIPTION
CH
CL
ML
ML-OL
MH-OH High-Plasticity Silt to High-Plasticity, Organic Silt
CL-ML
High-Plasticity Clay
Low-Plasticity Clay
Low-Plasticity Silt
Low-Plasticity Clay to Low-Plasticity Silt
Low-Plasticity Silt to Low-Plasticity, Organic Silt
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80 90 100 110 120
PL
A
S
T
I
C
I
T
Y
I
N
D
E
X
LIQUID LIMIT
B3-5
CH
MH-OH
ML-OL
CL
ML
CL-ML
HIGH PLASTICITYLOW PLASTICITY
4 K 2 K 1 K AVERAGE
4000 2000 1000 --
44.3 44.3 44.3 44.3
68.3 68.3 68.3 68.3
4 K 2 K 1 K AVERAGE
53.7 53.7 53.7 53.7
1732 1063 764 --
1625 975 673 --
430
18
350
18
DRY DENSITY (PCF):
OTAY RANCH VILLAGE 7, R-8
06862-52-67
DIRECT SHEAR - ASTM D 3080
NORMAL STRESS TEST LOAD
WATER CONTENT (%):
PEAK SHEAR STRESS (PSF):
ULT.-E.O.T. SHEAR STRESS (PSF):
RESULTS
PEAK COHESION, C (PSF)
PROJECT NO.:
Tob
N
SAMPLE NO.:
SAMPLE DEPTH (FT):
B3-5
21
GEOLOGIC UNIT:
NATURAL/REMOLDED:
INITIAL CONDITIONS
FRICTION ANGLE (DEGREES)
ULTIMATE COHESION, C (PSF)
FRICTION ANGLE (DEGREES)
NORMAL STRESS TEST LOAD
ACTUAL NORMAL STRESS (PSF):
WATER CONTENT (%):
AFTER TEST CONDITIONS
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 0.05 0.1 0.15 0.2 0.25 0.3
SH
E
A
R
S
T
R
E
S
S
(
P
S
F
)
HORIZONTAL DEFORMATION (IN)
4 K 2 K 1 K
4 K PEAK 2 K PEAK 1 K PEAK
4 K ULTIMATE 2 K ULTIMATE 1 K ULTIMATE
1 K
2 K
4 K
0
1000
2000
3000
4000
5000
6000
7000
0 1000 2000 3000 4000 5000 6000
SH
E
A
R
S
T
R
E
S
S
(
P
S
F
)
NORMAL STRESS (PSF)
0
1000
2000
3000
4000
5000
6000
7000
0 1000 2000 3000 4000 5000 6000
SH
E
A
R
S
T
R
E
S
S
(
P
S
F
)
NORMAL STRESS (PSF)
APPENDIX C
Geocon Project No. 06862-52-67 - C-1 - November 18, 2021
Revised May 9, 2024
APPENDIX C
SLOPE STABILITY ANALYSIS
We performed slope stability analyses using a two-dimensional computer software GeoStudio 2018
developed by Geo-Slope International Ltd. We analyzed the critical modes of potential slip surfaces
including rotational-mode and block-mode based on Spencer’s method. The soil parameters used, case
conditions, and the calculated factors of safety were presented herein. Plots of analyses results, including
the soil stratigraphy, potential failure surfaces, and calculated Factors of Safety, are included in this
appendix.
Shear strength characters of the existing geologic units were estimated based on laboratory direct shear tests
on samples obtained during our field investigation in accordance with ASTM D 3080 (see Appendix B)
and based on empirical data obtained from the referenced geotechnical literature. Table C-I presents the
soil parameters used for the stability analyses.
TABLE C-I
SUMMARY OF SOIL PROPERTIES USED FOR SLOPE STABILITY ANALYSES
Geologic Unit/Material Density (pcf) Cohesion (psf) Friction Angle (degrees)
Compacted Fill (Qcf) 130 300 28
Otay Formation (To) 130 325 33
Otay Formation Bentonite (Tob) 130 50 10
We selected Geologic Cross-Sections A-A’ through D-D’ to perform the slope stability analyses. Table C-
II provides a summary of cases analyzed and calculated factors of safety. A minimum Factor of Safety of
1.5 under static conditions is currently required by the City of Chula Vista for slope stability. Results of
slope stability analyses generated by GeoStudio 2018 are plotted herein. As discussed herein, we
encountered claystone layers in several of the exploratory borings within the Otay Formation. The claystone
possesses relatively low shear strengths and may be prone to slope instability if exposed in near cut and
natural slopes. Surficial slope stability calculations are presented herein.
Geocon Project No. 06862-52-67 - C-2 - November 18, 2021
Revised May 9, 2024
TABLE C-II
SUMMARY OF SLOPE STABILITY ANALYSES
Cross
Section File Name Condition of Slope Stability Analyses Calculated
Factor of Safety
A-A’
A-A_Case 1 Minimum FOS, Tob Plane, Block–Mode Analysis,
Static Condition 1.30
A-A_Case 2 Minimum FOS, Tob Plane, Block–Mode Analysis,
Static Condition – 20-foot buttress 1.57
A-A_Case 2 Minimum Factor of Safety (FOS), Rotational–Mode
Analysis, Static Condition 2.00
B-B’
B-B_Case 1 Minimum FOS, Tob Plane, Block–Mode Analysis,
Static Condition 1.53
B-B_Case 1 Minimum Factor of Safety (FOS), Rotational–Mode
Analysis, Static Condition 1.81
C-C’
C-C_Case 1 Minimum FOS, Tob Plane, Block–Mode Analysis,
Static Condition 1.42
C-C_Case 2 Minimum FOS, Tob Plane, Block–Mode Analysis,
Static Condition – 15-Foot Buttress 1.55
C-C_Case 2 Minimum Factor of Safety (FOS), Rotational–Mode
Analysis, Static Condition 2.04
D-D’
D-D_Case 1 Minimum FOS, Tob Plane, Block–Mode Analysis,
Static Condition 1.90
D-D_Case 1 Minimum Factor of Safety (FOS), Rotational–Mode
Analysis, Static Condition 2.08
1.30
Distance, Ft.
0 50 100 150 200 250 300 350
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
ToTo
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: A-A_Case 1.gszDate: 11/09/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section A-A'
Name: A-A_Case 1.gsz
Date: 11/09/2021 Time: 07:52:06 AM
Qcf Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing GradeProposed Grade
Tob
El. = 438' MSL
To
Site Limits
1.57
Distance, Ft.
0 50 100 150 200 250 300 350
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
ToTo
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: A-A_Case 2.gszDate: 11/09/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section A-A'
Name: A-A_Case 2.gsz
Date: 11/09/2021 Time: 07:58:31 AM
Qcf Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing GradeProposed Grade
Tob
El. = 438' MSL
To
Site Limits
20-ft Buttress
2.00
Distance, Ft.
0 50 100 150 200 250 300 350
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
ToTo
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: A-A_Case 2.gszDate: 11/09/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section A-A'
Name: A-A_Case 2.gsz
Date: 11/09/2021 Time: 08:30:28 AM
Qcf Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing GradeProposed Grade
Tob
El. = 438' MSL
To
Site Limits
20-ft Buttress
1.53
Distance, Ft.
0 50 100 150 200 250 300 350 400 450
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
To
To
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: B-B_Case 1.gszDate: 11/09/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section B-B'
Name: B-B_Case 1.gsz
Date: 11/09/2021 Time: 08:37:20 AM
Qcf
Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing Grade
Proposed Grade
Tob
El. = 440' MSL
To
1.81
Distance, Ft.
0 50 100 150 200 250 300 350 400 450
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
To
To
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: B-B_Case 1.gszDate: 11/09/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section B-B'
Name: B-B_Case 1.gsz
Date: 11/09/2021 Time: 08:37:37 AM
Qcf
Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing Grade
Proposed Grade
Tob
El. = 440' MSL
To
1.42
Distance, Ft.
0 50 100 150 200 250 300
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
To
To
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: C-C_Case 1.gszDate: 11/10/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section C-C'
Name: C-C_Case 1.gsz
Date: 11/10/2021 Time: 09:17:02 AM
QcfQcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing Grade
Proposed Grade
Tob
El. = 441' MSL
To
Site Limits
1.55
Distance, Ft.
0 50 100 150 200 250 300
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
To
To
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: C-C_Case 3-Proposed-Block.gszDate: 05/07/2024
Otay Ranch V7 - South
Project No. 06862-52-67
Section C-C'
Name: C-C_Case 3-Proposed-Block.gsz
Date: 05/07/2024 Time: 02:47:57 PM
Qcf
Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing Grade
Proposed Grade
Tob
El. = 441' MSL
To
Site Limits
15' Buttress
2.04
Distance, Ft.
0 50 100 150 200 250 300
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
To
To
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: C-C_Case 3-Proposed-Cir.gszDate: 05/07/2024
Otay Ranch V7 - South
Project No. 06862-52-67
Section C-C'
Name: C-C_Case 3-Proposed-Cir.gsz
Date: 05/07/2024 Time: 02:11:05 PM
Qcf
Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
Qcf 130 300 28
To 130 325 33
Tob 130 50 10
Existing Grade
Proposed Grade
Tob
El. = 441' MSL
To
Site Limits
15' Buttress
1.90
Distance, Ft.
-50 0 50 100 150 200 250 300 350
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
To
To
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: D-D_Case 1.gszDate: 11/11/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section D-D'
Name: D-D_Case 1.gsz
Date: 11/11/2021 Time: 11:38:10 AM
Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
To 130 325 33
Tob 130 50 10
Existing Grade
Proposed Grade
Tob
El. = 440' MSL
To
2.08
Distance, Ft.
-50 0 50 100 150 200 250 300 350
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
El
e
v
a
t
i
o
n
,
F
t
.
M
S
L
350
400
450
500
550
To
To
Directory: S:\Engineering and Geology\ENGINEER PROGRAMS, GUIDES, ETC\EngrgPrg\GEO-SLOPE2018\06862-52-67 OTR V7 S\File Name: D-D_Case 1.gszDate: 11/11/2021
Otay Ranch V7 - South
Project No. 06862-52-67
Section D-D'
Name: D-D_Case 1.gsz
Date: 11/11/2021 Time: 11:38:10 AM
Qcf
Material Properties:
Color Name Unit
Weight
(pcf)
Cohesion'
(psf)
Phi'
(°)
To 130 325 33
Tob 130 50 10
Existing Grade
Proposed Grade
Tob
El. = 440' MSL
To
APPENDIX D
APPENDIX D
RECOMMENDED GRADING SPECIFICATIONS
FOR
OTAY RANCH VILLAGE 7 SOUTH
CHULA VISTA, CALIFORNIA
PROJECT NO. 06862-52-67
GI rev. 07/2015
RECOMMENDED GRADING SPECIFICATIONS
1. GENERAL
1.1 These Recommended Grading Specifications shall be used in conjunction with the
Geotechnical Report for the project prepared by Geocon. The recommendations contained
in the text of the Geotechnical Report are a part of the earthwork and grading specifications
and shall supersede the provisions contained hereinafter in the case of conflict.
1.2 Prior to the commencement of grading, a geotechnical consultant (Consultant) shall be
employed for the purpose of observing earthwork procedures and testing the fills for
substantial conformance with the recommendations of the Geotechnical Report and these
specifications. The Consultant should provide adequate testing and observation services so
that they may assess whether, in their opinion, the work was performed in substantial
conformance with these specifications. It shall be the responsibility of the Contractor to
assist the Consultant and keep them apprised of work schedules and changes so that
personnel may be scheduled accordingly.
1.3 It shall be the sole responsibility of the Contractor to provide adequate equipment and
methods to accomplish the work in accordance with applicable grading codes or agency
ordinances, these specifications and the approved grading plans. If, in the opinion of the
Consultant, unsatisfactory conditions such as questionable soil materials, poor moisture
condition, inadequate compaction, and/or adverse weather result in a quality of work not in
conformance with these specifications, the Consultant will be empowered to reject the
work and recommend to the Owner that grading be stopped until the unacceptable
conditions are corrected.
2. DEFINITIONS
2.1 Owner shall refer to the owner of the property or the entity on whose behalf the grading
work is being performed and who has contracted with the Contractor to have grading
performed.
2.2 Contractor shall refer to the Contractor performing the site grading work.
2.3 Civil Engineer or Engineer of Work shall refer to the California licensed Civil Engineer
or consulting firm responsible for preparation of the grading plans, surveying and verifying
as-graded topography.
2.4 Consultant shall refer to the soil engineering and engineering geology consulting firm
retained to provide geotechnical services for the project.
GI rev. 07/2015
2.5 Soil Engineer shall refer to a California licensed Civil Engineer retained by the Owner,
who is experienced in the practice of geotechnical engineering. The Soil Engineer shall be
responsible for having qualified representatives on-site to observe and test the Contractor's
work for conformance with these specifications.
2.6 Engineering Geologist shall refer to a California licensed Engineering Geologist retained
by the Owner to provide geologic observations and recommendations during the site
grading.
2.7 Geotechnical Report shall refer to a soil report (including all addenda) which may include
a geologic reconnaissance or geologic investigation that was prepared specifically for the
development of the project for which these Recommended Grading Specifications are
intended to apply.
3. MATERIALS
3.1 Materials for compacted fill shall consist of any soil excavated from the cut areas or
imported to the site that, in the opinion of the Consultant, is suitable for use in construction
of fills. In general, fill materials can be classified as soil fills, soil-rock fills or rock fills, as
defined below.
3.1.1 Soil fills are defined as fills containing no rocks or hard lumps greater than
12 inches in maximum dimension and containing at least 40 percent by weight of
material smaller than ¾ inch in size.
3.1.2 Soil-rock fills are defined as fills containing no rocks or hard lumps larger than
4 feet in maximum dimension and containing a sufficient matrix of soil fill to allow
for proper compaction of soil fill around the rock fragments or hard lumps as
specified in Paragraph 6.2. Oversize rock is defined as material greater than
12 inches.
3.1.3 Rock fills are defined as fills containing no rocks or hard lumps larger than 3 feet
in maximum dimension and containing little or no fines. Fines are defined as
material smaller than ¾ inch in maximum dimension. The quantity of fines shall be
less than approximately 20 percent of the rock fill quantity.
3.2 Material of a perishable, spongy, or otherwise unsuitable nature as determined by the
Consultant shall not be used in fills.
3.3 Materials used for fill, either imported or on-site, shall not contain hazardous materials as
defined by the California Code of Regulations, Title 22, Division 4, Chapter 30, Articles 9
GI rev. 07/2015
and 10; 40CFR; and any other applicable local, state or federal laws. The Consultant shall
not be responsible for the identification or analysis of the potential presence of hazardous
materials. However, if observations, odors or soil discoloration cause Consultant to suspect
the presence of hazardous materials, the Consultant may request from the Owner the
termination of grading operations within the affected area. Prior to resuming grading
operations, the Owner shall provide a written report to the Consultant indicating that the
suspected materials are not hazardous as defined by applicable laws and regulations.
3.4 The outer 15 feet of soil-rock fill slopes, measured horizontally, should be composed of
properly compacted soil fill materials approved by the Consultant. Rock fill may extend to
the slope face, provided that the slope is not steeper than 2:1 (horizontal:vertical) and a soil
layer no thicker than 12 inches is track-walked onto the face for landscaping purposes. This
procedure may be utilized provided it is acceptable to the governing agency, Owner and
Consultant.
3.5 Samples of soil materials to be used for fill should be tested in the laboratory by the
Consultant to determine the maximum density, optimum moisture content, and, where
appropriate, shear strength, expansion, and gradation characteristics of the soil.
3.6 During grading, soil or groundwater conditions other than those identified in the
Geotechnical Report may be encountered by the Contractor. The Consultant shall be
notified immediately to evaluate the significance of the unanticipated condition.
4. CLEARING AND PREPARING AREAS TO BE FILLED
4.1 Areas to be excavated and filled shall be cleared and grubbed. Clearing shall consist of
complete removal above the ground surface of trees, stumps, brush, vegetation, man-made
structures, and similar debris. Grubbing shall consist of removal of stumps, roots, buried
logs and other unsuitable material and shall be performed in areas to be graded. Roots and
other projections exceeding 1½ inches in diameter shall be removed to a depth of 3 feet
below the surface of the ground. Borrow areas shall be grubbed to the extent necessary to
provide suitable fill materials.
4.2 Asphalt pavement material removed during clearing operations should be properly
disposed at an approved off-site facility or in an acceptable area of the project evaluated by
Geocon and the property owner. Concrete fragments that are free of reinforcing steel may
be placed in fills, provided they are placed in accordance with Section 6.2 or 6.3 of this
document.
GI rev. 07/2015
4.3 After clearing and grubbing of organic matter and other unsuitable material, loose or
porous soils shall be removed to the depth recommended in the Geotechnical Report. The
depth of removal and compaction should be observed and approved by a representative of
the Consultant. The exposed surface shall then be plowed or scarified to a minimum depth
of 6 inches and until the surface is free from uneven features that would tend to prevent
uniform compaction by the equipment to be used.
4.4 Where the slope ratio of the original ground is steeper than 5:1 (horizontal:vertical), or
where recommended by the Consultant, the original ground should be benched in
accordance with the following illustration.
TYPICAL BENCHING DETAIL
Remove All
Unsuitable Material
As Recommended By
Consultant
Finish Grade Original Ground
Finish Slope Surface
Slope To Be Such That
Sloughing Or Sliding
Does Not Occur Varies
“B”
See Note 1
No Scale
See Note 2
1
2
DETAIL NOTES: (1) Key width "B" should be a minimum of 10 feet, or sufficiently wide to permit
complete coverage with the compaction equipment used. The base of the key should
be graded horizontal, or inclined slightly into the natural slope.
(2) The outside of the key should be below the topsoil or unsuitable surficial material
and at least 2 feet into dense formational material. Where hard rock is exposed in the
bottom of the key, the depth and configuration of the key may be modified as
approved by the Consultant.
4.5 After areas to receive fill have been cleared and scarified, the surface should be moisture
conditioned to achieve the proper moisture content, and compacted as recommended in
Section 6 of these specifications.
GI rev. 07/2015
5. COMPACTION EQUIPMENT
5.1 Compaction of soil or soil-rock fill shall be accomplished by sheepsfoot or segmented-steel
wheeled rollers, vibratory rollers, multiple-wheel pneumatic-tired rollers, or other types of
acceptable compaction equipment. Equipment shall be of such a design that it will be
capable of compacting the soil or soil-rock fill to the specified relative compaction at the
specified moisture content.
5.2 Compaction of rock fills shall be performed in accordance with Section 6.3.
6. PLACING, SPREADING AND COMPACTION OF FILL MATERIAL
6.1 Soil fill, as defined in Paragraph 3.1.1, shall be placed by the Contractor in accordance with
the following recommendations:
6.1.1 Soil fill shall be placed by the Contractor in layers that, when compacted, should
generally not exceed 8 inches. Each layer shall be spread evenly and shall be
thoroughly mixed during spreading to obtain uniformity of material and moisture
in each layer. The entire fill shall be constructed as a unit in nearly level lifts. Rock
materials greater than 12 inches in maximum dimension shall be placed in
accordance with Section 6.2 or 6.3 of these specifications.
6.1.2 In general, the soil fill shall be compacted at a moisture content at or above the
optimum moisture content as determined by ASTM D 1557.
6.1.3 When the moisture content of soil fill is below that specified by the Consultant,
water shall be added by the Contractor until the moisture content is in the range
specified.
6.1.4 When the moisture content of the soil fill is above the range specified by the
Consultant or too wet to achieve proper compaction, the soil fill shall be aerated by
the Contractor by blading/mixing, or other satisfactory methods until the moisture
content is within the range specified.
6.1.5 After each layer has been placed, mixed, and spread evenly, it shall be thoroughly
compacted by the Contractor to a relative compaction of at least 90 percent.
Relative compaction is defined as the ratio (expressed in percent) of the in-place
dry density of the compacted fill to the maximum laboratory dry density as
determined in accordance with ASTM D 1557. Compaction shall be continuous
over the entire area, and compaction equipment shall make sufficient passes so that
the specified minimum relative compaction has been achieved throughout the
entire fill.
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6.1.6 Where practical, soils having an Expansion Index greater than 50 should be placed
at least 3 feet below finish pad grade and should be compacted at a moisture
content generally 2 to 4 percent greater than the optimum moisture content for the
material.
6.1.7 Properly compacted soil fill shall extend to the design surface of fill slopes. To
achieve proper compaction, it is recommended that fill sl opes be over-built by at
least 3 feet and then cut to the design grade. This procedure is considered
preferable to track-walking of slopes, as described in the following paragraph.
6.1.8 As an alternative to over-building of slopes, slope faces may be back-rolled with a
heavy-duty loaded sheepsfoot or vibratory roller at maximum 4-foot fill height
intervals. Upon completion, slopes should then be track-walked with a D-8 dozer
or similar equipment, such that a dozer track covers all slope surfaces at least
twice.
6.2 Soil-rock fill, as defined in Paragraph 3.1.2, shall be placed by the Contractor in accordance
with the following recommendations:
6.2.1 Rocks larger than 12 inches but less than 4 feet in maximum dimension may be
incorporated into the compacted soil fill, but shall be limited to the area measured
15 feet minimum horizontally from the slope face and 5 feet below finish grade or
3 feet below the deepest utility, whichever is deeper.
6.2.2 Rocks or rock fragments up to 4 feet in maximum dimension may either be
individually placed or placed in windrows. Under certain conditions, rocks or rock
fragments up to 10 feet in maximum dimension may be placed using similar
methods. The acceptability of placing rock materials greater than 4 feet in
maximum dimension shall be evaluated during grading as specific cases arise and
shall be approved by the Consultant prior to placement.
6.2.3 For individual placement, sufficient space shall be provided between rocks to allow
for passage of compaction equipment.
6.2.4 For windrow placement, the rocks should be placed in trenches excavated in
properly compacted soil fill. Trenches should be approximately 5 feet wide and
4 feet deep in maximum dimension. The voids around and beneath rocks should be
filled with approved granular soil having a Sand Equivalent of 30 or greater and
should be compacted by flooding. Windrows may also be placed utilizing an
"open-face" method in lieu of the trench procedure, however, this method should
first be approved by the Consultant.
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6.2.5 Windrows should generally be parallel to each other and may be placed either
parallel to or perpendicular to the face of the slope depending on the site geometry.
The minimum horizontal spacing for windrows shall be 12 feet center-to-center
with a 5-foot stagger or offset from lower courses to next overlying course. The
minimum vertical spacing between windrow courses shall be 2 feet from the top of
a lower windrow to the bottom of the next higher windrow.
6.2.6 Rock placement, fill placement and flooding of approved granular soil in the
windrows should be continuously observed by the Consultant.
6.3 Rock fills, as defined in Section 3.1.3, shall be placed by the Contractor in accordance with
the following recommendations:
6.3.1 The base of the rock fill shall be placed on a sloping surface (minimum slope of 2
percent). The surface shall slope toward suitable subdrainage outlet facilities. The
rock fills shall be provided with subdrains during construction so that a hydrostatic
pressure buildup does not develop. The subdrains shall be permanently connected
to controlled drainage facilities to control post-construction infiltration of water.
6.3.2 Rock fills shall be placed in lifts not exceeding 3 feet. Placement shall be by rock
trucks traversing previously placed lifts and dumping at the edge of the currently
placed lift. Spreading of the rock fill shall be by dozer to facilitate seating of the
rock. The rock fill shall be watered heavily during placement. Watering shall
consist of water trucks traversing in front of the current rock lift face and spraying
water continuously during rock placement. Compaction equipment with
compactive energy comparable to or greater than that of a 20-ton steel vibratory
roller or other compaction equipment providing suitable energy to achieve the
required compaction or deflection as recommended in Paragraph 6.3.3 shall be
utilized. The number of passes to be made should be determined as described in
Paragraph 6.3.3. Once a rock fill lift has been covered with soil fill, no additional
rock fill lifts will be permitted over the soil fill.
6.3.3 Plate bearing tests, in accordance with ASTM D 1196, may be performed in both
the compacted soil fill and in the rock fill to aid in determining the required
minimum number of passes of the compaction equipment. If performed, a
minimum of three plate bearing tests should be performed in the properly
compacted soil fill (minimum relative compaction of 90 percent). Plate bearing
tests shall then be performed on areas of rock fill having two passes, four passes
and six passes of the compaction equipment, respectively. The number of passes
required for the rock fill shall be determined by comparing the results of the plate
bearing tests for the soil fill and the rock fill and by evaluating the deflection
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variation with number of passes. The required number of passes of the compaction
equipment will be performed as necessary until the plate bearing deflections are
equal to or less than that determined for the properly compacted soil fill. In no case
will the required number of passes be less than two.
6.3.4 A representative of the Consultant should be present during rock fill operations to
observe that the minimum number of “passes” have been obtained, that water is
being properly applied and that specified procedures are being followed. The actual
number of plate bearing tests will be determined by the Consultant during grading.
6.3.5 Test pits shall be excavated by the Contractor so that the Consultant can state that,
in their opinion, sufficient water is present and that voids between large rocks are
properly filled with smaller rock material. In-place density testing will not be
required in the rock fills.
6.3.6 To reduce the potential for “piping” of fines into the rock fill from overlying soil
fill material, a 2-foot layer of graded filter material shall be placed above the
uppermost lift of rock fill. The need to place graded filter material below the rock
should be determined by the Consultant prior to commencing grading. The
gradation of the graded filter material will be determined at the time the rock fill is
being excavated. Materials typical of the rock fill should be submitted to the
Consultant in a timely manner, to allow design of the graded filter prior to the
commencement of rock fill placement.
6.3.7 Rock fill placement should be continuously observed during placement by the
Consultant.
7. SUBDRAINS
7.1 The geologic units on the site may have permeability characteristics and/or fracture
systems that could be susceptible under certain conditions to seepage. The use of canyon
subdrains may be necessary to mitigate the potential for adverse impacts associated with
seepage conditions. Canyon subdrains with lengths in excess of 500 feet or extensions of
existing offsite subdrains should use 8-inch-diameter pipes. Canyon subdrains less than 500
feet in length should use 6-inch-diameter pipes.
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TYPICAL CANYON DRAIN DETAIL
7.2 Slope drains within stability fill keyways should use 4-inch-diameter (or lager) pipes.
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TYPICAL STABILITY FILL DETAIL
7.3 The actual subdrain locations will be evaluated in the field during the remedial grading
operations. Additional drains may be necessary depending on the conditions observed and
the requirements of the local regulatory agencies. Appropriate subdrain outlets should be
evaluated prior to finalizing 40-scale grading plans.
7.4 Rock fill or soil-rock fill areas may require subdrains along their down-slope perimeters to
mitigate the potential for buildup of water from construction or landscape irrigation. The
subdrains should be at least 6-inch-diameter pipes encapsulated in gravel and filter fabric.
Rock fill drains should be constructed using the same requirements as canyon subdrains.
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7.5 Prior to outletting, the final 20-foot segment of a subdrain that will not be extended during
future development should consist of non-perforated drainpipe. At the non-perforated/
perforated interface, a seepage cutoff wall should be constructed on the downslope side of
the pipe.
TYPICAL CUT OFF WALL DETAIL
7.6 Subdrains that discharge into a natural drainage course or open space area should be
provided with a permanent headwall structure.
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TYPICAL HEADWALL DETAIL
7.7 The final grading plans should show the location of the proposed subdrains. After
completion of remedial excavations and subdrain installation, the project civil engineer
should survey the drain locations and prepare an “as-built” map showing the drain
locations. The final outlet and connection locations should be determined during grading
operations. Subdrains that will be extended on adjacent projects after grading can be placed
on formational material and a vertical riser should be placed at the end of the subdrain. The
grading contractor should consider videoing the subdrains shortly after burial to check
proper installation and functionality. The contractor is responsible for the performance of
the drains.
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8. OBSERVATION AND TESTING
8.1 The Consultant shall be the Owner’s representative to observe and perform tests during
clearing, grubbing, filling, and compaction operations. In general, no more than 2 feet in
vertical elevation of soil or soil-rock fill should be placed without at least one field density
test being performed within that interval. In addition, a minimum of one field density test
should be performed for every 2,000 cubic yards of soil or soil-rock fill placed and
compacted.
8.2 The Consultant should perform a sufficient distribution of field density tests of the
compacted soil or soil-rock fill to provide a basis for expressing an opinion whether the fill
material is compacted as specified. Density tests shall be performed in the compacted
materials below any disturbed surface. When these tests indicate that the density of any
layer of fill or portion thereof is below that specified, the particular layer or areas
represented by the test shall be reworked until the specified density has been achieved.
8.3 During placement of rock fill, the Consultant should observe that the minimum number of
passes have been obtained per the criteria discussed in Section 6.3.3. The Consultant
should request the excavation of observation pits and may perform plate bearing tests on
the placed rock fills. The observation pits will be excavated to provide a basis for
expressing an opinion as to whether the rock fill is properly seated and sufficient moisture
has been applied to the material. When observations indicate that a layer of rock fill or any
portion thereof is below that specified, the affected layer or area shall be reworked until the
rock fill has been adequately seated and sufficient moisture applied.
8.4 A settlement monitoring program designed by the Consultant may be conducted in areas of
rock fill placement. The specific design of the monitoring program shall be as
recommended in the Conclusions and Recommendations section of the project
Geotechnical Report or in the final report of testing and observation services performed
during grading.
8.5 We should observe the placement of subdrains, to check that the drainage devices have
been placed and constructed in substantial conformance with project specifications.
8.6 Testing procedures shall conform to the following Standards as appropriate:
8.6.1 Soil and Soil-Rock Fills:
8.6.1.1 Field Density Test, ASTM D 1556, Density of Soil In-Place By the
Sand-Cone Method.
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8.6.1.2 Field Density Test, Nuclear Method, ASTM D 6938, Density of Soil and
Soil-Aggregate In-Place by Nuclear Methods (Shallow Depth).
8.6.1.3 Laboratory Compaction Test, ASTM D 1557, Moisture-Density
Relations of Soils and Soil-Aggregate Mixtures Using 10-Pound
Hammer and 18-Inch Drop.
8.6.1.4. Expansion Index Test, ASTM D 4829, Expansion Index Test.
9. PROTECTION OF WORK
9.1 During construction, the Contractor shall properly grade all excavated surfaces to provide
positive drainage and prevent ponding of water. Drainage of surface water shall be
controlled to avoid damage to adjoining properties or to finished work on the site. The
Contractor shall take remedial measures to prevent erosion of freshly graded areas until
such time as permanent drainage and erosion control features have been installed. Areas
subjected to erosion or sedimentation shall be properly prepared in accordance with the
Specifications prior to placing additional fill or structures.
9.2 After completion of grading as observed and tested by the Consultant, no further
excavation or filling shall be conducted except in conjunction with the services of the
Consultant.
10. CERTIFICATIONS AND FINAL REPORTS
10.1 Upon completion of the work, Contractor shall furnish Owner a certification by the Civil
Engineer stating that the lots and/or building pads are graded to within 0.1 foot vertically of
elevations shown on the grading plan and that all tops and toes of slopes are within 0.5 foot
horizontally of the positions shown on the grading plans. After installation of a section of
subdrain, the project Civil Engineer should survey its location and prepare an as-built plan
of the subdrain location. The project Civil Engineer should verify the proper outlet for the
subdrains and the Contractor should ensure that the drain system is free of obstructions.
10.2 The Owner is responsible for furnishing a final as-graded soil and geologic report
satisfactory to the appropriate governing or accepting agencies. The as-graded report
should be prepared and signed by a California licensed Civil Engineer experienced in
geotechnical engineering and by a California Certified Engineering Geologist, indicating
that the geotechnical aspects of the grading were performed in substantial conformance
with the Specifications or approved changes to the Specifications.
Geocon Project No. 06862-52-67 November 18, 2021
Revised May 9, 2024
LIST OF REFERENCES
1.2022 California Building Code, California Code of Regulations, Title 24, Part 2, based on the
2021 International Building Code, prepared by California Building Standards Commission,
dated July 2022.
2.American Concrete Institute, ACI 318-11, Building Code Requirements for Structural Concrete
and Commentary, dated August, 2011.
3.ACI 330-21, Commercial Concrete Parking Lots and Site Paving Design and Construction,
prepared by the American Concrete Institute, dated May 2021.
4.American Society of Civil Engineers (ASCE), ASCE 7-16, Minimum Design Loads and
Associated Criteria for Buildings and Other Structures, 2017.
5.California Department of Conservation, Division of Mines and Geology, Probabilistic Seismic
Hazard Assessment for the State of California, Open File Report 96-08, 1996.
6.County of San Diego, San Diego County Multi Jurisdiction Hazard Mitigation Plan, San Diego,
California – Final Draft, dated 2017.
7.Historical Aerial Photos. http://www.historicaerials.com
8.Jennings, C. W., 1994, California Division of Mines and Geology, Fault Activity Map of
California and Adjacent Areas, California Geologic Data Map Series Map No. 6.
9.Todd, V. R., 2004, Preliminary Geologic Map of the El Cajon 30’x60’ Quadrangle, Southern
California, Version 1.0, Open-File Report 2004-1361 Scale 1:100,000.
10.Special Publication 117A, Guidelines For Evaluating and Mitigating Seismic Hazards in
California 2008, California Geological Survey, Revised and Re-adopted September 11, 2008.
11.Unpublished reports, aerial photographs, and maps on file with Geocon Incorporated.
12.USGS computer program, Seismic Hazard Curves and Uniform Hazard Response Spectra,
http://geohazards.usgs.gov/designmaps/us/application.php.