HomeMy WebLinkAboutTechnical Report 5 - R-4 Site GeotechnicalUPDATE
GEOTECHNICAL REPORT
OTAY RANCH VILLAGE 7
NEIGHBORHOOD R-4
CHULA VISTA, CALIFORNIA
PREPARED FOR
OCTOBER 25, 2022
REVISED MAY 8, 2024
PROJECT NO. 06862-52-66A
GROCON
INCORPORATED
GEOTECHNICAL • ENVIRONMENTAL MATERIALSO
6960 Flanders Drive • San Diego, California 92121-2974 • Telephone 858.558.6900 • Fax 858.558.6159
Project No. 06862-52-66A
October 25, 2022
Revised May 8, 2024
Baldwin & Sons, Inc.
610 West Ash Street, Suite 1500
San Diego, California 92101
Attention: Ms. Maria Miller
Subject: UPDATE GEOTECHNICAL REPORT
OTAY RANCH VILLAGE 7
NEIGHBORHOOD R-4
CHULA VISTA, CALIFORNIA
Dear Ms. Miller:
In accordance with your request and our proposal No. LG-22461, dated September 29, 2022, we
prepared this update geotechnical report for the subject project. The accompanying report presents the
results of our study and conclusions and recommendations pertaining to the geotechnical aspects of
proposed development of the site. We revised this report to address the 3rd party comments prepared by
Michael Baker International.
The site was partially graded as part of the Village 7 project and recently sheet-graded as part of the
Otay Ranch Village 8 West development, The site is located south of Santa Luna Street, east of La
Media Road and west and north of Village 8 West in Chula Vista, California. Provided the
recommendations contained in this update report are followed, the site is considered suitable for
construction and support of the proposed development.
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.PREVIOUS SITE DEVELOPMENT .............................................................................................. 2
3.SITE AND PROJECT DESCRIPTION ........................................................................................... 2
4.SOIL AND GEOLOGIC CONDITIONS ........................................................................................ 4
4.1 Compacted Fill (Qcf) ............................................................................................................. 4
4.2 Otay Formation (To) .............................................................................................................. 4
5.GROUNDWATER .......................................................................................................................... 5
6.GEOLOGIC HAZARDS ................................................................................................................. 5
6.1 Regional Faulting and Seismicity .......................................................................................... 5
6.2 Ground Rupture ..................................................................................................................... 6
6.3 Liquefaction ........................................................................................................................... 6
6.4 Storm Surge, Tsunamis, and Seiches ..................................................................................... 7
6.5 Landslides .............................................................................................................................. 7
6.6 Erosion ................................................................................................................................... 7
7.CONCLUSIONS AND RECOMMENDATIONS ........................................................................... 8
7.1 General ................................................................................................................................... 8
7.2 Excavation and Soil Characteristics ...................................................................................... 9
7.3 Seismic Design Criteria ....................................................................................................... 10
7.4 Grading ................................................................................................................................ 12
7.5 Temporary Excavations ....................................................................................................... 14
7.6 Foundation and Concrete Slabs-On-Grade Recommendations ........................................... 14
7.7 Exterior Concrete Flatwork ................................................................................................. 19
7.8 Retaining Walls ................................................................................................................... 21
7.9 Lateral Loading .................................................................................................................... 24
7.10 Slope Maintenance............................................................................................................... 25
7.11 Preliminary Pavement Recommendations ........................................................................... 25
7.12 Preliminary Paver Recommendations .................................................................................. 29
7.13 Site Drainage and Moisture Protection ................................................................................ 32
7.14 Grading and Foundation Plan Review ................................................................................. 33
7.15 Testing and Observation Services During Construction ...................................................... 33
LIMITATIONS AND UNIFORMITY OF CONDITIONS
MAPS AND ILLUSTRATIONS
Figure 1, Geologic Map
APPENDIX A
LABORATORY TESTING
APPENDIX B
RECOMMENDED GRADING SPECIFICATIONS
LIST OF REFERENCES
Geocon Project No. 06862-52-66A - 1 - October 25, 2022
Revised May 8, 2024
UPDATE GEOTECHNICAL REPORT
1. PURPOSE AND SCOPE
This report presents the results of our update geotechnical study for Neighborhood R-4 in the Otay
Ranch Village 7 development. The site is located south of Santa Luna Street, east of La Media Road and
north and west of Otay Ranch Village 8 West. The site is located in the City of Chula Vista, California
as shown on the Vicinity Map.
Vicinity Map
The purpose of this update report is to provide foundation design criteria, concrete flatwork design
criteria, retaining wall and lateral load recommendations and excavation and remedial grading
recommendations. The scope of the study also included a review of:
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.Final Report of Testing and Observation Services Performed During Site Grading, Otay Ranch Village 8 West, Santa Luna Off-Site, Chula Vista, California, prepared by Geocon Incorporated, dated October 26, 2020 (Project No. 06862-52-66).
3.Site Plan, Santa Luna, Chula Vista, California, prepared by AO Architecture, dated October 5, 2023. (Job No. 2022-314).
Geocon Project No. 06862-52-66A - 2 - October 25, 2022
Revised May 8, 2024
2. PREVIOUS SITE DEVELOPMENT
The site was partially graded during development of Otay Ranch Village 7, Neighborhood R-2 in 2006.
Fill slopes were constructed to facilitate the construction of La Media Road and Santa Luna Street with
portions of these slopes extending onto the R-4 site. We provided testing and observation services during
the prior grading operations. Before additional grading in 2020, the site was used as storm water
management area with a basin and storm drain structure.
The most recent phase of grading (2020) consisted of removing surficial topsoil and weathered portions
of the Otay Formation, installing a canyon subdrain and placing compacted fill to achieve the sheet-
graded condition. In addition, a storm drain headwall and concrete pipe was removed in the northwest
corner of the site. We provided testing and observation services during the most recent grading
operations. The referenced grading report dated October 26, 2020 presents a summary of the
observations, compaction test results, and professional opinions pertaining to the grading. The remedial
grading operations exposed the underlying Otay Formation and benching of existing fill was performed
during placement of compacted fill. A portion of the Otay Formation was left in place as it was out of
previous limits of grading. A southerly flowing canyon subdrain was installed subsequent to removals
in the canyon and tied into an existing subdrain on the Village 8 West property. The approximate
location of the subdrain is shown on the Geologic Map, Figure 1. Formational materials were excavated
and compacted fill was placed to achieve the current as-graded conditions. The Geologic Map, Figure
1, presents the units encountered at the site.
3. SITE AND PROJECT DESCRIPTION
The Neighborhood R-4 site is located at the southern end of Village 7, south of Santa Luna Street and
the Vortec Site, east of La Media Road and west and north of the Otay Ranch Village 8 West
development. The site is currently covered in seasonal grasses and is in a sheet-graded condition with
drainage directed towards a basin in the southwest corner of the site. A northern slope ascends to Santa
Luna Street with a maximum height of about 15 feet. A slope ascends to the Otay Ranch Village 8 West
development on the south side of the property with a maximum height of about 15 feet. Access to the
site is currently from La Media Road on the southwest corner of the property. The Existing Site Map
shows the current conditions of the site.
Geocon Project No. 06862-52-66A - 3 - October 25, 2022
Revised May 8, 2024
Existing Site Map
The proposed development of the R-4 site includes the construction of an apartment building (up to 4
stories) with parking areas, leasing and fitness building, amenity space, retaining walls, utilities and
landscaping. The site will be accessed by entrances along La Media Road and Santa Luna Street.
Grading for Neighborhood R-4 will generally consist of cuts and fills between approximately 5 and 10
feet. The Site plan shows the planned development.
Site Plan
Geocon Project No. 06862-52-66A - 4 - October 25, 2022
Revised May 8, 2024
The locations and descriptions of the site and proposed development are based on the referenced rough
grading plans and our understanding of project development. If project details vary significantly from
those described herein, Geocon Incorporated should be contacted to evaluate the necessity for review
and revision of this report.
4. SOIL AND GEOLOGIC CONDITIONS
The existing soil and geologic conditions include compacted fill and the Otay Formation. The
approximate lateral extent of the geologic units is shown on the Geologic Map, Figure 1. The geologic
units are described herein in order of increasing age. Compacted fill underlies most of the R-4 site with
the Otay Formation is exposed at grade in a small cut slope in the northern portion of the site. We tested
soil samples obtained at the existing surface elevations during previous grading operations as presented
in Appendix A.
4.1 Compacted Fill (Qcf)
In general, the compacted fill placed in 2006 and 2020 at the site consists of sandy silt and clayey to
silty sand derived from the Otay Formation. The fill thickness varies up to about 40 feet thick. We
performed testing and observation services during the previous grading operations as discussed herein.
The fill materials possess a “low” to “medium” expansion potential (expansion index of between 21 and
90) and a “S0” water-soluble sulfate content. The existing compacted fill is adequate to support the
proposed development. However, remedial grading of the upper materials will be required as discussed
herein.
4.2 Otay Formation (To)
Dense to very dense, grayish brown, silty sandstone, siltstone, and sandy claystone of the Otay
Formation is exposed at grade in a small cut slope in the northern portion of the site This unit is typically
moderately to well cemented and very difficult excavation may be encountered. In addition, oversize
concretions may be generated during grading operations that may require export. The formational
materials are considered suitable for the support of structures or additional fill loads; however, remedial
grading will be required as discussed herein.
Bentonitic claystone typically exists within the Otay Formation that consists of a highly expansive
claystone with a waxy texture that is laterally continuous. The bentonitic claystone beds consist of highly
expansive clays, which typically exhibit low shear strength. We did not encounter this unit during
previous grading operations and do not expect to encounter this claystone during construction.
Geocon Project No. 06862-52-66A - 5 - October 25, 2022
Revised May 8, 2024
5. GROUNDWATER
We did not encounter groundwater during the investigation or during previous grading operations.
Groundwater is not expected to adversely impact the development of the site. It is not uncommon for
groundwater or seepage conditions to develop where none previously existed. Groundwater elevations
are dependent on seasonal precipitation, irrigation, and land use, among other factors, and vary as a
result. Proper surface drainage will be important to future performance of the project.
6. GEOLOGIC HAZARDS
6.1 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
Geocon Project No. 06862-52-66A - 6 - October 25, 2022
Revised May 8, 2024
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.
Earthquakes in Southern California
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.
6.2 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.
6.3 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.
Geocon Project No. 06862-52-66A - 7 - October 25, 2022
Revised May 8, 2024
6.4 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 waterfront. The site is
located greater than 9 miles from the Pacific Ocean and is at an elevation of about 460 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.
6.5 Landslides
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.
6.6 Erosion
The site is relatively flat and is not located adjacent to the Pacific Ocean coast or a free-flowing drainage
where active erosion is occurring. 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.
Geocon Project No. 06862-52-66A - 8 - October 25, 2022
Revised May 8, 2024
7. CONCLUSIONS AND RECOMMENDATIONS
7.1 General
7.1.1 We did not encounter soil or geologic conditions during previous geotechnical investigations
or grading operations that, in our opinion, would preclude the continued development of the
property as presently planned provided that the recommendations of this report are followed.
7.1.2 With the exception of possible moderate to strong seismic shaking, we did not observe or
know of significant geologic hazards to exist on the site that would adversely affect the
proposed project.
7.1.3 The upper, weathered portions of the Otay Formation, and upper portions of the compacted
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 existing fill and Otay
Formation are considered suitable for the support of proposed fill and structural loads.
7.1.4 We did not encounter groundwater during our subsurface exploration or during the grading
operations 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 the
grading operations on the western portion of the site at the lower elevations of the remedial
excavations. Seepage may be encountered during grading operations, especially during the
rainy season.
7.1.5 Excavation of the 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.
7.1.6 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.
7.1.7 Surface settlement monuments and additional canyon subdrains will not be required on this
project.
Geocon Project No. 06862-52-66A - 9 - October 25, 2022
Revised May 8, 2024
7.2 Excavation and Soil Characteristics
7.2.1 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.
7.2.2 The soil encountered during previous grading operations is considered to be “expansive”
(expansion index [EI] of greater than 20) as defined by 2022 California Building Code (CBC)
Section 1803.5.3. We expect a majority of the soil encountered possess a “low” to “medium”
expansion potential (EI of between 20 and 90) in accordance with ASTM D 4829. Table 7.2
presents soil classifications based on the expansion index.
TABLE 7.2
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
7.2.3 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
different concentrations. Additionally, over time landscaping activities (i.e., addition of
fertilizers and other soil nutrients) may affect the concentration.
7.2.4 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.
Geocon Project No. 06862-52-66A - 10 - October 25, 2022
Revised May 8, 2024
7.3 Seismic Design Criteria
7.3.1 Table 7.3.1 summarizes site-specific design criteria obtained from the 2022 California
Building Code (CBC; Based on the 2018 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 7.3.1
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
0.764g 0.764g Figure 1613.2.1(1)
MCER Ground Motion Spectral Response
Acceleration – Class B (1 sec), S1
0.277g 0.277g Figure 1613.2.1(2)
Site Coefficient, FA 1.200 1.200 Table 1613.2.3(1)
Site Coefficient, FV 1.500* 2.045* Table 1613.2.3(2)
Site Class Modified MCER Spectral Response
Acceleration (short), SMS
0.916g 0.916g Section 1613.2.3 (Eqn
16-36)
Site Class Modified MCER Spectral Response
Acceleration – (1 sec), SM1
0.416g* 0.567g* Section 1613.2.3 (Eqn
16-37)
5% Damped Design
Spectral Response Acceleration (short), SDS
0.611g 0.611g Section 1613.2.4 (Eqn
16-38)
5% Damped Design
Spectral Response Acceleration (1 sec), SD1
0.277g* 0.378g* Section 1613.2.4 (Eqn
16-39)
*See following paragraph
7.3.2 Using the code-based values presented in this Table 7.3.1, in lieu of a 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 indicates that the ground
Geocon Project No. 06862-52-66A - 11 - October 25, 2022
Revised May 8, 2024
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.
7.3.3 Table 7.3.2 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 7.3.2
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 0.332g 0.332g Figure 22-9
Site Coefficient, FPGA 1.200 1.268 Table 11.8-1
Site Class Modified MCEG
Peak Ground Acceleration, PGAM
0.398g 0.421g Section 11.8.3 (Eqn 11.8-1)
7.3.4 Conformance to the criteria in Tables 7.3.1 and 7.3.2 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.
7.3.5 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 7.3.3 presents a
summary of the risk categories in accordance with ASCE 7-16.
Geocon Project No. 06862-52-66A - 12 - October 25, 2022
Revised May 8, 2024
TABLE 7.3.3
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
7.4 Grading
7.4.1 Grading should be performed in accordance with the recommendations provided in this report,
the Recommended Grading Specifications contained in Appendix B 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.
7.4.2 Prior to commencing grading operations, a preconstruction meeting should be held at the site
with the owner or developer, grading contractor, city representative, civil engineer and
geotechnical engineer in attendance. Special soil handling and/or the grading plans can be
discussed at that time.
7.4.3 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.
7.4.4 The upper 1 to 2 feet of the existing fill should be processed or removed, moisture conditioned
as necessary, and compacted prior to placing fill. Deeper excavations may be required if dry,
saturated or soft soil is encountered (e.g. in the area of the desilting basin). In addition,
building pads with formational cut-fill transitions and pads underlain by formational materials
should be undercut a minimum of 3 feet and replaced with properly compacted fill. The upper
3 feet of the building pads should be composed of compacted fill. Undercuts should be sloped
Geocon Project No. 06862-52-66A - 13 - October 25, 2022
Revised May 8, 2024
a minimum of 1 percent and drain toward the adjacent on-site streets or driveways. The
undercut and formational excavations should extend at least 5 feet outside of the planned
building areas.
7.4.5 The City of Chula Vista requires that the upper 5 feet of fill soil and the upper 3 feet of
formational materials within the public right-of-way or public easement possess an expansion
index of 90 or less. If material with an expansion index greater than 90 is exposed within the
right-of-ways, the upper 5 feet of compacted fills and the upper 3 feet of formational should
be removed and replaced with fill with an expansion index of 90 or less. Proposed alternative
methods should be approved by the City of Chula Vista within the right-of-way areas.
7.4.6 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 7.4.1 provides a summary of the grading recommendations.
TABLE 7.4.1
SUMMARY OF GRADING RECOMMENDATIONS
Area Remedial Grading Excavation
Recommendations
Site Development
Process Upper 1 to 2 Feet of Existing Fill
Undercut Upper 3 Feet of Formational Materials
Below Finish Grade
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
7.4.7 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.
Geocon Project No. 06862-52-66A - 14 - October 25, 2022
Revised May 8, 2024
7.4.8 Import fill (if necessary) should consist of the characteristics presented in Table 7.4.2. 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 7.4.2
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
7.5 Temporary Excavations
7.5.1 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
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.
7.5.2 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.
7.6 Foundation and Concrete Slabs-On-Grade Recommendations
7.6.1 The foundation recommendations herein are for proposed buildings up to 4 stories. The proposed
buildings can be supported on a shallow foundation system founded in the compacted fill.
Foundations for the structure should consist of continuous strip footings and/or isolated spread
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. Table 7.6.1 provides a summary of the
foundation design recommendations. Based on review of the laboratory test results performed
during mass grading, we expect majority of the soil encountered on site is planned to possess a
“very low” to “medium” expansion potential (expansion index of 90 or less).
Geocon Project No. 06862-52-66A - 15 - October 25, 2022
Revised May 8, 2024
TABLE 7.6.1
SUMMARY OF FOUNDATION RECOMMENDATIONS
Parameter Value
Minimum Continuous Foundation Width 12 inches
Minimum Isolated Foundation Width 24 inches
Minimum Foundation Depth 24 Inches Below Lowest Adjacent Grade
Minimum Steel Reinforcement 4 No. 5 Bars, 2 at the Top and 2 at the Bottom
Allowable Bearing Capacity 2,500 psf
Bearing Capacity Increase 500 psf per Foot of Depth
300 psf per Foot of Width
Maximum Allowable Bearing Capacity 4,000 psf
Estimated Total Settlement 1 Inch
Estimated Differential Settlement ½ Inch in 40 Feet
Footing Size Used for Settlement 7-Foot Square
Design Expansion Index 90 or less
7.6.2 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
7.6.3 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.
7.6.4 The concrete slab-on-grades should be a designed in accordance with Table 7.6.2.
Geocon Project No. 06862-52-66A - 16 - October 25, 2022
Revised May 8, 2024
TABLE 7.6.2
CONCRETE SLAB-ON-GRADE RECOMMENDATIONS BY CATEGORY
Minimum Concrete Slab
Thickness (inches)
Interior Slab
Reinforcement Typical Slab Underlayment
5 No. 3 bars at 18 inches on
center, both directions
3 to 4 Inches of
Sand/Gravel/Base
7.6.5 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.
7.6.6 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 to 4 inches of sand
below the concrete slab-on-grade 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 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.
7.6.7 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. If a post-tensioned system is being used, the proposed buildings would
be designated with a Foundation Category once grading is completed. The post-tensioned
systems 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 7.6.3 for the particular Foundation Category designated. The
Geocon Project No. 06862-52-66A - 17 - October 25, 2022
Revised May 8, 2024
parameters presented in Table 7.6.3 are based on the guidelines presented in the PTI DC 10.5
design manual.
TABLE 7.6.3
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PTI) DC10.5 Design Parameters Foundation Category
Thornthwaite Index -20
Equilibrium Suction 3.9
Edge Lift Moisture Variation Distance, eM (Feet) 4.9
Edge Lift, yM (Inches) 1.58
Center Lift Moisture Variation Distance, eM (Feet) 9.0
Center Lift, yM (Inches) 0.66
7.6.8 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.
7.6.9 If the structural engineer proposes a post-tensioned foundation design method other than PTI,
DC 10.5:
The deflection criteria presented in Table 7.6.3 are still applicable.
Interior stiffener beams should be used.
The width of the perimeter foundations should be at least 12 inches.
The perimeter footing embedment depths should be at least and 24 inches. The
embedment depths should be measured from the lowest adjacent pad grade.
7.6.10 Our experience indicates post-tensioned slabs are susceptible to excessive edge lift, 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. Current PTI design
procedures primarily address the potential center lift of slabs but, because of the placement of
the reinforcing tendons in the top of the slab, the resulting eccentricity after tensioning reduces
the ability of the system to mitigate edge lift. The structural engineer should design the
foundation system to reduce the potential of edge lift occurring for the proposed structures.
7.6.11 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
Geocon Project No. 06862-52-66A - 18 - October 25, 2022
Revised May 8, 2024
beams and the slab during the construction of the post-tension foundation system unless
designed by the project structural engineer.
7.6.12 Isolated footings, if present, should have the minimum embedment depth and width
recommended for conventional foundations.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. Where this condition cannot be avoided, the isolated footings
should be connected to the building foundation system with grade beams in both directions.
7.6.13 Where buildings or other improvements are planned near the top of a slope steeper than 3:1
(horizontal:vertical), special foundations and/or design considerations are recommended due
to the tendency for lateral soil movement to occur.
For fill slopes less than 20 feet high, building 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.
When located next to a descending 3:1 (horizontal: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. An acceptable alternative to deepening the footings would be the use of
a post-tensioned slab and foundation system or increased footing and slab
reinforcement. 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 recommendations 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 that would permit some lateral soil
movement without causing extensive distress. Geocon Incorporated should be
consulted for specific recommendations.
Geocon Project No. 06862-52-66A - 19 - October 25, 2022
Revised May 8, 2024
7.6.14 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 that would permit some lateral soil movement without causing
extensive distress. Geocon Incorporated should be consulted for specific recommendations.
7.6.15 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.
7.6.16 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 (ACI) 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.
7.6.17 We should observe the foundation excavations prior to the placement of reinforcing steel and
concrete to check that the exposed soil conditions are similar to those expected and that they
have been extended to the appropriate bearing strata. Foundation modifications may be
required if unexpected soil conditions are encountered.
7.6.18 We should provide additional design parameters as required by the project structural engineer.
7.7 Exterior Concrete Flatwork
7.7.1 Exterior concrete flatwork not subject to vehicular traffic should be constructed in accordance
with the recommendations presented in Table 7.7. The recommended steel reinforcement
would help reduce the potential for cracking.
Geocon Project No. 06862-52-66A - 20 - October 25, 2022
Revised May 8, 2024
TABLE 7.7
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
EI < 130 4x4-W4.0/W4.0 (4x4-4/4) welded wire mesh 4 Inches No. 4 Bars 12 inches on center, Both Directions
*In excess of 8 feet square.
7.7.2 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.
7.7.3 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.
7.7.4 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
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.
7.7.5 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.
Geocon Project No. 06862-52-66A - 21 - October 25, 2022
Revised May 8, 2024
7.7.6 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.
7.8 Retaining Walls
7.8.1 Retaining walls should be designed using the values presented in Table 7.8.1. Soil with an
expansion index (EI) of greater than 90 should not be used as backfill material behind
retaining walls.
TABLE 7.8.1
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
7.8.2 The project retaining walls should be designed as shown in the Retaining Wall Loading
Diagram.
Geocon Project No. 06862-52-66A - 22 - October 25, 2022
Revised May 8, 2024
Retaining Wall Loading Diagram
7.8.3 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.
7.8.4 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.
7.8.5 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.
7.8.6 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
Geocon Project No. 06862-52-66A - 23 - October 25, 2022
Revised May 8, 2024
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
7.8.7 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.
7.8.8 In general, wall foundations should be designed in accordance with Table 7.8.2. 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 7.8.2
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
7.8.9 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
Geocon Project No. 06862-52-66A - 24 - October 25, 2022
Revised May 8, 2024
stabilized earth [MSE] walls, soil nail walls, or soldier pile walls) are planned, Geocon
Incorporated should be consulted for additional recommendations.
7.8.10 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.
7.8.11 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.
7.8.12 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
7.9 Lateral Loading
7.9.1 Table 7.9 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.
TABLE 7.9
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*
Geocon Project No. 06862-52-66A - 25 - October 25, 2022
Revised May 8, 2024
*Per manufacturer’s recommendations.
7.9.2 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..
7.10 Slope Maintenance
7.10.1 Slopes that are steeper than 3:1 (horizontal:vertical) may, under conditions which are both
difficult to prevent and predict, be susceptible to near surface (surficial) slope instability. The
instability is typically limited to the outer three feet of a portion of the slope and usually does
not directly impact the improvements on the pad areas above or below the slope. The
occurrence of surficial instability is more prevalent on fill slopes and is generally preceded by
a period of heavy rainfall, excessive irrigation, or the migration of subsurface seepage. The
disturbance and/or loosening of the surficial soils, as might result from root growth, soil
expansion, or excavation for irrigation lines and slope planting, may also be a significant
contributing factor to surficial instability. It is, therefore, recommended that, to the maximum
extent practical: (a) disturbed/loosened surficial soils be either removed or properly
recompacted, (b) irrigation systems be periodically inspected and maintained to eliminate
leaks and excessive irrigation, and (c) surface drains on and adjacent to slopes be periodically
maintained to preclude ponding or erosion. It should be noted that although the incorporation
of the above recommendations should reduce the potential for surficial slope instability, it
will not eliminate the possibility, and, therefore, it may be necessary to rebuild or repair a
portion of the project's slopes in the future.
7.11 Preliminary Pavement Recommendations
7.11.1 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 assumed an R-Value
of 10 and 78 for the subgrade soil and base materials, respectively, for the purposes of this
preliminary analysis. Table 7.11.1 presents the preliminary flexible pavement sections.
Geocon Project No. 06862-52-66A - 26 - October 25, 2022
Revised May 8, 2024
TABLE 7.11.1
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 and fire-
truck traffic 7.0 10 4 15
7.11.2 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
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.
7.11.3 Base materials should conform to Section 26-1.02B of the Standard Specifications for The
State of California Department of Transportation (Caltrans) with a ¾-inch maximum size
aggregate. Asphalt concrete should conform to Section 203-6 of the Standard Specifications
for Public Works Construction (Greenbook).
7.11.4 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 alternate design
parameters are requested.
7.11.5 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 7.11.2
provides the traffic categories and design parameters used for the calculations for 20-year
design life.
Geocon Project No. 06862-52-66A - 27 - October 25, 2022
Revised May 8, 2024
TABLE 7.11.2
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
7.11.6 We used the parameters presented in Table 7.11.3 to calculate the pavement design sections.
We should be contacted to provide updated design sections, if necessary.
TABLE 7.11.3
RIGID PAVEMENT DESIGN PARAMETERS
Design Parameter Design Value
Modulus of subgrade reaction, k 50 pci
Modulus of rupture for concrete, MR 500 psi
Concrete Compressive Strength 3,000 psi
Traffic Category, TC A and C
Average daily truck traffic, ADTT 10 and 100
7.11.7 Based on the criteria presented herein, the PCC pavement sections should have a minimum
thickness as presented in Table 7.11.4.
TABLE 7.11.4
RIGID VEHICULAR PAVEMENT RECOMMENDATIONS
Traffic Category Trucks Per Day Portland Cement
Concrete, T (Inches)
A = Car Parking Areas and Access Lanes 10 6
B = Entrance and Truck Service Lanes 50 6½
E = Garbage or Fire Truck Lanes 5 7½
7.11.8 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.
Geocon Project No. 06862-52-66A - 28 - October 25, 2022
Revised May 8, 2024
7.11.9 Adequate joint spacing should be incorporated into the design and construction of the rigid
pavement in accordance with Table 7.11.5.
TABLE 7.11.5
MAXIMUM JOINT SPACING
Pavement Thickness, T (Inches) Maximum Joint Spacing (Feet)
4<T<5 10
5<T<6 12.5
6<T 15
7.11.10 The rigid pavement should also be designed and constructed incorporating the parameters
presented in Table 7.11.6.
TABLE 7.11.6
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
7.11.11 Reinforcing steel will not be necessary within the concrete for geotechnical purposes with the
possible exception of dowels at construction joints as discussed herein.
7.11.12 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 determined by the referenced ACI report.
Geocon Project No. 06862-52-66A - 29 - October 25, 2022
Revised May 8, 2024
7.11.13 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.
7.11.14 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.
7.12 Preliminary Paver Recommendations
7.12.1 We calculated the paver section 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. Based on the Interlocking Concrete Pavement Institute
(ICPI), the pavers should possess a minimum thickness of 3⅛ inches overlying 1 to 1½ inch
of sand. We used an equivalent asphalt concrete section equal to the thickness of the pavers
of approximately 3 inches in accordance with Interlocking Concrete Pavement Institute (ICPI)
Tech Spec Number 4. In addition, the pavers should be installed in a pattern appropriate for
vehicular traffic. Table 7.12.1 presents two options for the paver underlayment: compacted
base materials or aggregate.
Geocon Project No. 06862-52-66A - 30 - October 25, 2022
Revised May 8, 2024
TABLE 7.12.1
PERMEABLE PAVER PAVEMENT SECTION
Location
Traffic
Index
(TI)
Assumed
Subgrade
R-Value
Equivalent
Paver
Asphalt
Concrete
Thickness
(inches)
Option 1 Option 2
Estimated
Sand
Thickness
(inches)
Base
Materials
(inches
ASTM C 33
Aggregate
Parking stalls
for
automobiles
and light-duty
vehicles
5.0 10 3 1 -1½ 9
3” Sand /
3” #8 /
7” #57
Driveways for
automobiles
and light-duty
vehicles
5.5 10 3 1 -1½ 11
3” Sand /
3” #8 /
9” #57
Medium truck
traffic areas 6.0 10 3 1 -1½ 13
3” Sand /
3” #8 /
11” #57
Driveways for
heavy truck
traffic
7.0 10 3 1 -1½ 17
3” Sand /
3” #8 /
15” #57
7.12.2 Class 2 base, crushed aggregate base, or rigid pavement (with thicknesses described herein)
can be used below the non-storm water quality decorative pavers. As an alternative, concrete
with the thickness at locations described herein can be placed beneath the non-storm water
decorative pavers.
7.12.3 The aggregate presented in Option 2 should be in conformance with ASTM C33 as shown in
Table 7.12.2.
Geocon Project No. 06862-52-66A - 31 - October 25, 2022
Revised May 8, 2024
TABLE 7.12.2
AGGREGATE GRADATION LIMITS PER ASTM C33
Sieve Size
Percent Passing Sieves
Choker Sand No. 8 No. 57
1.5 Inches -- -- 100
1 Inch -- -- 95-100
0.5 Inch -- 100 25-60
0.375 Inch 100 85-100 --
No. 4 95-100 10-30 0-10
No. 8 80-100 0-10 0-5
No. 16 50-85 0-5 --
No. 30 25-60 -- --
No. 50 5-30 -- --
No. 100 0-10 -- --
No. 200 0-3 -- --
7.12.4 Prior to placing base/aggregate materials, 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
determined by ASTM D 1557. The depth of compaction should be at least 12 inches.
Similarly, the base materials 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.
7.12.5 The pavers should be installed and maintained in accordance with the manufacturer’s
recommendations. The future owners should be made aware and responsible for the
maintenance program. In addition, pavers tend to shift vertically and horizontally during the
life of the pavement and should be expected. The pavers should be placed tightly adjacent to
each other and the spacing between the paver units should be filled with appropriate filler. A
polymer sand (Poly-Sand) can be used on the decorative, non-storm water quality paver area
to help prevent water infiltration.
7.12.6 The pavers normally require a concrete border to prevent lateral movement from traffic. The
concrete border surrounding the pavers should be embedded at least 6 inches into the subgrade
to reduce the potential for water migration to the adjacent landscape areas and pavement areas.
The side liners are not necessary if the concrete borders are installed as discussed herein.
Geocon Project No. 06862-52-66A - 32 - October 25, 2022
Revised May 8, 2024
7.12.7 The performance of pavement is highly dependent on providing positive surface drainage
away from the edge of the pavement. Ponding of water on or adjacent to the pavement will
likely result in pavement distress and subgrade failure. Drainage from landscaped areas should
be directed to controlled drainage structures. Landscape areas adjacent to the edge of
pavements are not recommended due to the potential for surface or irrigation water to infiltrate
the underlying permeable aggregate base and cause distress. Where such a condition cannot
be avoided, consideration should be given to incorporating measures that will significantly
reduce the potential for subsurface water migration into the aggregate base. If planter islands
are planned, the perimeter curb should extend at least 6 inches below the level of the base
materials.
7.13 Site Drainage and Moisture Protection
7.13.1 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.
7.13.2 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.
7.13.3 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.
7.13.4 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.
Geocon Project No. 06862-52-66A - 33 - October 25, 2022
Revised May 8, 2024
7.14 Grading and Foundation Plan Review
7.14.1 We should review the precise grading and foundation plans to check that the plans have been
prepared in substantial conformance with the recommendations of this report.
7.15 Testing and Observation Services During Construction
7.15.1 Geocon Incorporated should provide geotechnical testing and observation services during
the grading operations, foundation construction, utility installation, retaining wall backfill
and pavement installation. Table 7.15 presents the typical geotechnical observations we
would expect for the proposed improvements.
TABLE 7.15
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
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. 06862-52-66A October 25, 2022
Revised May 8, 2024
LIMITATIONS AND UNIFORMITY OF CONDITIONS
1.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.
2.This report is issued with the understanding that it is the responsibility of the owner, or of 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.
3.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.
4.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.
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OTAY RANCH
VILLAGE 8 WEST
(GRADED BY OTHERS)
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BASIN
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To
PREVIOUSLY EXISTING
HEADWALL STRUCTURE-
NOW REMOVED
SUBDRAIN CONNECTED
TO EXISTING DRAIN ON
VILLAGE 8 WEST SITE
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 8:58AM | By:RUBEN AGUILAR | File Location:Y:\PROJECTS\06862-52-66A (OTR V7 - Nbhd R-4)\SHEETS\06862-52-66A Geo Map.dwg
GEOTECHNICAL ENVIRONMENTAL MATERIALS
1" =
GEOLOGIC 1AP
OTAY RANCH VILLAGE 7
NEIGHBORHOOD R-4
CHULA VISTA, CALIFORNIA
40'05 - 08 - 2024
06862 - 52 - 66A
1 1 1
........COMPACTED FILL (Geocon, 2006 and 2020)
........OTAY FORMATION (Dotted Where Buried)
........APPROX. LOCATION GEOLOGIC CONTACT
........APPROX. LOCATION OF SUBDRAIN
........APPROX. ELEVATION OF SUBDRAIN (In Feet, MSL)
........APPROX. ELEVATION AT BASE OF FILL (In Feet, MSL)
GEOCON LEGEND
431
420
Qcf
To
APPENDIX A
Geocon Project No. 06862-52-66A October 25, 2022
Revised May 8, 2024
APPENDIX A
PREVIOUS LABORATORY TESTING
We tested laboratory samples of material used for fill during grading to evaluate moisture-density
relationships, optimum moisture content and maximum dry density (ASTM D 1557) and performed
laboratory tests on materials within the upper 3 to 4 feet of the existing sheet graded pad subsequent to the
completion of grading operations in 2020. We performed laboratory testing in general accordance with the
test methods of the American Society for Testing and Materials (ASTM) or other suggested procedures.
We tested samples to evaluate expansion characteristics and water-soluble sulfate content. The results of
our laboratory tests are presented in tables herein.
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.)
1 Gray, fine to coarse, Sandy SILT 117.3 14.1
2 Light grayish brown, Clayey SAND; trace gravel 122.3 11.5
3 Light olive gray, Clayey SAND; trace silt 116.1 14.1
SUMMARY OF LABORATORY EXPANSION INDEX TEST RESULTS
ASTM D 4829
Sample No. (Location)
Moisture Content (%) Dry Density (pcf) Expansion Index 2022 CBC Classification
ASTM Soil Expansion Classification Before Test After Test
EI-1 (West) 14.9 30.2 94.1 65 Expansive Medium
EI-2 (East) 14.9 31.2 93.8 69 Expansive Medium
SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS
CALIFORNIA TEST NO. 417
Sample No. Water-Soluble Sulfate (%) Sulfate Severity Exposure
EI-1 (West) 0.023 S0
EI-2 (East) 0.030 S0
APPENDIX B
APPENDIX B
RECOMMENDED GRADING SPECIFICATIONS
FOR
OTAY RANCH VILLAGE 7
NEIGHBORHOOD R-4
CHULA VISTA, CALIFORNIA
PROJECT NO. 06862-52-66A
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.
GI rev. 07/2015
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. 06862-52-66A October 25, 2022
Revised May 8, 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.ACI 318-19, Commentary on Building Code Requirements for Structural Concrete, prepared by
the American Concrete Institute, dated May 2019.
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.Kennedy, M. P., and S. S. Tan, Geologic Map of the San Diego 30’x60’ Quadrangle, California,
USGS Regional Map Series Map No. 3, Scale 1:100,000, 2005.
10.Todd, Victoria R., Preliminary Geologic Map of the El Cajon 30’ x 60’ Quadrangle, Southern
California, USGS, Open File Report 2004-1361, Scale 1:100,000, 2004.
11.Special Publication 117A, Guidelines For Evaluating and Mitigating Seismic Hazards in
California 2008, California Geological Survey, Revised and Re-adopted September 11, 2008
12.Unpublished Geotechnical Reports and Information, Geocon Incorporated.
13.USGS computer program, Seismic Hazard Curves and Uniform Hazard Response Spectra,
http://earthquake.usgs.gov/research/hazmaps/design/.