HomeMy WebLinkAboutPreliminary Geotechnical Investigation and Infiltration StudyReport
Preliminary Geotechnical Investigation and Infiltration Study
Bonita Glen Apartments
Bonita Glen Drive, Chula Vista, California
PREPARED FOR
Silvergate Development, LLC
4980 N Harbor Drive, Suite 203
San Diego, CA 92106
PREPARED BY
NOVA Services, Inc.
4373 Viewridge Ave, Ste. B
San Diego, California 92123
NOVA Project No. 2017826
December 4, 2017
G E O T E C H N I C A L Ŷ M A T E R I A L S Ŷ S P E C I A L I N S P E C T I O N S
S B E Ŷ S L B E Ŷ S C O O P
4373 Viewridge Avenue, Ste. B
San Diego, CA 92123
858.292.7575
Mr. Tommy Edmunds December 4, 2017
Silvergate Development, LLC NOVA Project 2017826
4980 N Harbor Drive, Suite 203
San Diego, CA 92106
Subject: Report
Preliminary Geotechnical Investigation and Infiltration Study
Bonita Glen Apartments
Bonita Glen Drive, Chula Vista, California
Dear Mr. Edmunds:
NOVA Services, Inc. (NOVA) is pleased to present herewith its report of the above-referenced
geotechnical investigation. The work reported was completed by NOVA for Silvergate Development
LLC in accordance with NOVA’s proposal dated October 26, 2016.
NOVA appreciates the opportunity to be of continued service to Silvergate Development LLC for its
developments in the San Diego region. In the meantime, should you have any questions regarding this
report or other matters, please do not hesitate to contact the undersigned at (858) 292-7575.
Sincerely,
NOVA Services, Inc.
________________ _________________________
Wail Mokhtar Bryan Miller-Hicks, P.E., G.E.
Project Manager Senior Geologist
__________________________
John F. O’Brien, P.E., G.E.
Principal Geotechnical Engineer
Report
Preliminary Geotechnical Investigation and Infiltration Study
Bonita Glen Apartments, Chula Vista, California
______________________________________________________________
Table of Contents
1.0 INTRODUCTION.............................................................................................................. 1
1.1 Terms of Reference.........................................................................................................................1
1.2 Objective, Scope, and Limitations of This Work.........................................................................1
1.2.1 Objective......................................................................................................................................................1
1.2.2 Scope............................................................................................................................................................2
1.2.3 Limitations...................................................................................................................................................2
1.3 Organization of This Report..........................................................................................................3
2.0 PROJECT INFORMATION............................................................................................ 4
2.1 Location ...........................................................................................................................................4
2.2 Planned Development.....................................................................................................................4
2.2.1 Architectural.................................................................................................................................................4
2.2.2 Structural......................................................................................................................................................5
2.2.3 Stormwater BMPs........................................................................................................................................6
2.3 Below Grade Construction and Potential for Earthwork...........................................................7
2.3.1 Below Grade Construction...........................................................................................................................7
2.3.2 Potential for Earthwork................................................................................................................................7
3.0 FIELD EXPLORATION AND LABORATORY TESTING ........................................ 8
3.1 Overview..........................................................................................................................................8
3.2 Engineering Borings .......................................................................................................................9
3.2.1 General.........................................................................................................................................................9
3.2.2 Logging and Sampling.................................................................................................................................9
3.2.3 Closure.......................................................................................................................................................10
3.3 Percolation Testing .......................................................................................................................10
3.3.1 General.......................................................................................................................................................10
3.3.2 Drilling.......................................................................................................................................................10
3.3.3 Conversion to Percolation Wells................................................................................................................10
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3.3.4 Percolation Testing.....................................................................................................................................10
3.3.5 Closure.......................................................................................................................................................11
3.4 Geotechnical Laboratory Testing................................................................................................11
3.4.1 General.......................................................................................................................................................11
3.4.2 Compaction................................................................................................................................................11
3.4.3 Soil Gradation and Moisture......................................................................................................................11
3.4.4 R-Value......................................................................................................................................................12
3.4.5 Plasticity and Expansion Potential.............................................................................................................12
3.5 Corrosion Potential.......................................................................................................................13
4.0 SITE CONDITIONS........................................................................................................ 14
4.1 Geologic and Seismic Setting .......................................................................................................14
4.1.1 Regional.....................................................................................................................................................14
4.1.2 Site Specific ..............................................................................................................................................14
4.2 Site Specific Conditions................................................................................................................15
4.2.1 Surface .......................................................................................................................................................15
4.2.2 Subsurface..................................................................................................................................................16
4.2.3 Groundwater...............................................................................................................................................16
4.2.4 Surface Water.............................................................................................................................................16
5.0 REVIEW OF GEOLOGIC HAZARDS......................................................................... 18
5.1 Overview........................................................................................................................................18
5.2 Geologic Hazards..........................................................................................................................18
5.2.1 Strong Ground Motion...............................................................................................................................18
5.2.2 Landslide....................................................................................................................................................18
5.3 Soil Hazards...................................................................................................................................19
5.3.1 Embankment Stability................................................................................................................................19
5.3.2 Seismic.......................................................................................................................................................20
5.3.3 Expansive Soil............................................................................................................................................20
5.3.4 Hydro-Collapsible Soils.............................................................................................................................20
5.3.5 Corrosive Soils...........................................................................................................................................21
5.4 Other Hazards...............................................................................................................................21
5.4.1 Flood..........................................................................................................................................................21
5.4.2 Tsunami......................................................................................................................................................21
5.4.3 Seiche.........................................................................................................................................................22
6.0 EARTHWORK AND FOUNDATIONS........................................................................ 23
6.1 Overview........................................................................................................................................23
6.1.1 General.......................................................................................................................................................23
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6.1.2 Review and Surveillance............................................................................................................................23
6.2 Seismic Design Parameters ..........................................................................................................23
6.2.1 Site Class....................................................................................................................................................23
6.2.2 Seismic Design Parameters........................................................................................................................23
6.3 Corrosivity and Sulfates...............................................................................................................24
6.3.1 General.......................................................................................................................................................24
6.3.2 Metals.........................................................................................................................................................24
6.3.3 Sulfates and Concrete.................................................................................................................................25
6.3.4 Limitations.................................................................................................................................................26
6.4 Site Preparation and Earthwork.................................................................................................26
6.4.1 Establish Erosion and Sedimentation Control............................................................................................26
6.4.2 Clearing and Grubbing...............................................................................................................................26
6.4.3 Grading for Foundations............................................................................................................................26
6.4.4 Remedial Grading for Flatwork .................................................................................................................27
6.5 Shallow Foundations.....................................................................................................................27
6.5.1 Bearing Unit...............................................................................................................................................27
6.5.2 Minimum Dimensions and Reinforcing.....................................................................................................28
6.5.3 Allowable Contact Stress...........................................................................................................................28
6.5.4 Lateral Resistance ......................................................................................................................................28
6.5.5 Settlement...................................................................................................................................................28
6.5.6 Footing Construction and Inspection .........................................................................................................28
6.6 Ground Supported Slabs..............................................................................................................28
6.6.1 Conventionally Reinforced Slab-on-Grade................................................................................................28
6.6.2 Slab Setback from Slopes...........................................................................................................................29
6.6.3 Slope Maintenance.....................................................................................................................................29
6.6.4 Moisture Barrier.........................................................................................................................................29
6.7 Control of Drainage Around Structures.....................................................................................30
6.7.1 General.......................................................................................................................................................30
6.7.2 Landscaping...............................................................................................................................................30
6.7.3 Drainage.....................................................................................................................................................30
6.7.4 Surface Grades...........................................................................................................................................31
6.7.5 Backfills.....................................................................................................................................................31
6.7.6 Utilities.......................................................................................................................................................31
6.8 Retaining Walls.............................................................................................................................31
6.8.1 General.......................................................................................................................................................31
6.8.2 Shallow Foundations..................................................................................................................................31
6.8.3 Lateral Earth Pressures...............................................................................................................................32
6.8.4 Foundation Uplift.......................................................................................................................................32
6.8.5 Resistance to Lateral Loads........................................................................................................................32
6.8.6 Wall Drainage............................................................................................................................................32
6.8.7 Seismic.......................................................................................................................................................32
6.9 Elevator Pits ..................................................................................................................................33
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6.10 Temporary Slopes.........................................................................................................................33
7.0 STORMWATER INFILTRATION............................................................................... 34
7.1 Overview........................................................................................................................................34
7.2 Infiltration Rates...........................................................................................................................34
7.2.1 General.......................................................................................................................................................34
7.2.2 Design Infiltration Rate..............................................................................................................................34
7.3 Review of Geotechnical Feasibility Criteria...............................................................................35
7.3.1 Overview....................................................................................................................................................35
7.3.2 Soil and Geologic Conditions ....................................................................................................................35
7.3.3 Settlement and Volume Change.................................................................................................................35
7.3.4 Slope Stability............................................................................................................................................35
7.3.5 Utilities.......................................................................................................................................................36
7.3.6 Groundwater Mounding.............................................................................................................................36
7.3.7 Retaining Walls and Foundations ..............................................................................................................36
7.3.8 Other Factors..............................................................................................................................................36
7.4 Suitability of the Site for Stormwater Infiltration.....................................................................36
8.0 PAVEMENTS .................................................................................................................. 37
8.1 General...........................................................................................................................................37
8.2 Setback from Slopes......................................................................................................................37
8.3 Subgrade Preparation...................................................................................................................37
8.3.1 Rough Grading...........................................................................................................................................37
8.3.2 Proof-Rolling .............................................................................................................................................38
8.3.3 Moisture Control........................................................................................................................................38
8.3.4 Surveillance................................................................................................................................................38
8.4 Flexible Pavements........................................................................................................................38
8.5 Rigid Pavements............................................................................................................................39
8.5.1 General.......................................................................................................................................................39
8.5.2 Jointing and Reinforcement .......................................................................................................................39
9.0 REFERENCES................................................................................................................. 40
9.1 Site Specific....................................................................................................................................40
9.2 Design.............................................................................................................................................40
9.3 Geologic and Site Setting..............................................................................................................40
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List of Plates
Plate 1: Subsurface Investigation Map
List of Appendices
Appendix A Use of this Report
Appendix B Soil Exploration Logs
Appendix C Records of Infiltration Testing
Appendix E Laboratory Analytical Results
List of Figures
Figure 1-1. Vicinity Map
Figure 2-1. Site Location and Limits
Figure 2-2. Conceptual Planning
Figure 2-3. Elevation View of the Four Level Apartment Building
Figure 2-4. Proposed Storm Drain System
Figure 3-1. Location of the Engineering and Percolation Test Borings
Figure 4-1. Geologic Mapping of the Site Vicinity
Figure 4-2. Site View from the East Along Vista Drive
Figure 4-3. Alignment and Limits of the Ephemeral Stream
Figure 5-1. Faulting in the Site Vicinity
Figure 5-2. Flood Mapping of the Site
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List of Tables
Table 3-1. Abstract of the Engineering Borings
Table 3-2. Abstract of the Percolation Testing
Table 3-3. Summary of the Compaction Testing, ASTM D 1557
Table 3-4. Abstract of the Soil Gradation and Moisture Content Testing
Table 3-5. Summary of the Corrosivity Testing
Table 6-1. Seismic Design Parameters, ASCE 7-10
Table 6-2. Summary of Corrosivity Testing of the Near Surface Soil
Table 6-3. Soil Resistivity and Corrosion Potential
Table 6-4. Exposure Categories and Requirements for Water-Soluble Sulfates
Table 6-5. Lateral Earth Pressures
Table 7-1. Infiltration Rates Determined by Percolation Testing
Table 8-1. Preliminary Recommendations for Flexible Pavements
Table 8-2. Recommended Concrete Requirements
Preliminary Geotechnical Investigation and Infiltration Study December 4, 2017
Bonita Glen Apartments, Chula Vista, CA NOVA Project 2017826
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1.0 INTRODUCTION
1.1 Terms of Reference
This report provides the findings of a geotechnical investigation for the development now known as
“Bonita Glen Apartments” located on Bonita Glen Drive in Chula Vista, California (hereafter, also
referenced as ‘the site’). The work reported herein was completed by NOVA Services, Inc. (NOVA) for
Silvergate Development LLC in accordance with NOVA’s proposal dated July 26, 2016.
Figure 1-1 depicts the vicinity of the planned Bonita Glen Apartments.
Figure 1-1. Vicinity Map
1.2 Objective, Scope, and Limitations of This Work
1.2.1 Objective
The objectives of the work reported herein are threefold, as described below.
1. Objective 1, Site Characterization. Characterize the subsurface conditions within the limits of the
planned Bonita Glen development (hereafter, also referenced as ‘the site’).
2. Objective 2, Geotechnical. Provide recommendations for geotechnical-related development,
including foundations and earthwork.
3. Objective 3, Stormwater. Provide recommendations for development of permanent stormwater
infiltration BMPs.
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1.2.2 Scope
In order to accomplish the above objectives, NOVA undertook the task-based scope of work described
below.
x Task 1, Background Review. Reviewed readily available background data regarding the site area,
including geotechnical reports, topographic maps, geologic data, fault maps, and preliminary
development plans for the project. Preliminary architectural and civil design information was also
reviewed.
x Task 2, Subsurface Exploration. The exploration includes the following subtasks.
o Subtask 2-1, Reconnaissance. Prior to undertaking any invasive work, NOVA conducted
a site reconnaissance, including layout of the exploratory borings used to explore the
subsurface conditions. Underground Service Alert was notified for underground utility
mark-out services.
o Subtask 2-2, Coordination. NOVA coordinated with Silvergate regarding access for
fieldwork. NOVA retained a specialty subcontractor to conduct the drilling.
o Subtask 2-3, Engineering Borings. A NOVA geologist directed drilling of six (6)
engineering borings, including two borings located within 50 feet of proposed DMAs.
o Subtask 2-4, Percolation Borings, and Testing. A NOVA geologist directed the drilling
of four (4) percolation test borings located within the DMA’s. Thereafter, percolation
testing was conducted in accordance with the requirements of the City of Chula Vista.
x Task 3, Laboratory Testing. Laboratory testing was undertaken to address index soil
characteristics and the potential that soils may be corrosive to embedded concrete or metals.
x Task 4, Engineering Evaluations. The findings of Tasks 1-3 were utilized to support geotechnical
and stormwater infiltration-related evaluations.
x Task 5, Reporting. This report presents the findings of all work, and completes NOVA’s scope of
work. The report addresses (i) development of foundation support for the separate structural
elements; and (ii) the siting and design of permanent stormwater infiltration BMPs.
1.2.3 Limitations
The recommendations included in this report are not final. These recommendations are developed by
NOVA using judgment and opinion and based upon the limited information available from the borings.
NOVA can finalize its recommendations only by observing actual subsurface conditions revealed during
construction. NOVA cannot assume responsibility or liability for the report's recommendations if NOVA
does not perform construction observation.
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This report does not address any environmental matters; including, but not limited to assessment or
investigation for the presence or absence of hazardous or toxic materials in the soil, groundwater, or
surface water within or beyond the site.
Appendix A provides additional discussion regarding limitations and use of this report.
1.3 Organization of This Report
The remainder of this report is organized as described below.
x Section 2 reviews the presently available project information.
x Section 3 describes the field investigation and laboratory testing.
x Section 4 describes the geologic and subsurface conditions.
x Section 5 reviews soil and geologic hazards that may affect the site.
x Section 6 provides recommendations for earthwork and foundations.
x Section 7 addresses stormwater infiltration.
x Section 8 provides recommendations for pavements.
x Section 9 lists the principal references used in evaluations for this report.
The report is supported by four appendices.
x Appendix A presents discussion regarding use of this report.
x Appendix B presents logs of borings.
x Appendix C provides records of percolation testing
x Appendix D provides records of geotechnical laboratory testing.
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2.0 PROJECT INFORMATION
2.1 Location
The subject property is an irregularly-shaped parcel identified as APN 570-131-11, 570-010-10, 570-140-
48 and 570-140-5, comprising about 5.3 acres of open, vacant land in the city of Chula Vista. The
property is bounded by Bonita Glen Drive on the south, and Vista Drive to the east and north.
Figure 2-1 depicts the location and limits of the planned development.
Figure 2-1. Site Location and Limits
2.2 Planned Development
2.2.1 Architectural
NOVA’s understanding of the proposed development is based on review of planning level architectural
graphics (reference, Bonita Glen Apartments, Studio E Architects, Project 16124, October 17, 2017).
This preliminary planning indicates the project will consist of seven residential buildings, six of which
will rise to three levels, with ‘tuck under’ parking at Level 1 and dwelling units at Level 2 and Level 3. A
seventh building will have three stories of residential use over one story of parking.
The seven residential structures will provide an aggregate of 170 dwelling units, with the seventh, four-
level structure containing 66 units. Infrastructure, consisting of landscaped areas, surface parking and a
variety of amenities, will support the development. Figure 2-2 (following page) depicts conceptual
planning for the layout of the planned development.
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Bonita Glen Apartments, Chula Vista, CA NOVA Project 2017826
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Figure 2-2. Conceptual Planning
(source: Studio E Architects 2017)
2.2.2 Structural
Design is still in preliminary stages. As a consequence of the preliminary nature of the design, structural
design has not begun. However, it is understood that design will adapt to ‘Type V-A over Type 1-A,’
allowing for development of wood framed residential units (Type V-A) atop a reinforced concrete podium
(Type 1-A). Figure 2- 3 provides an elevation view of the largest of the planned structures.
Figure 2-3. Elevation View of the Four Level Apartment Building
(source: Studio E Architects 2017)
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2.2.3 Stormwater BMPs
Preliminary civil planning by Latitude 33 (reference, Preliminary Drainage Study, Bonita Glen, Bonita
Glen Drive, Chula Vista, California 91910, Latitude 33 Planning & Engineering, Job 1522.00, undated)
describes planning for stormwater management.
The site is already drained by an ephemeral stream that runs approximately north-south through the
eastern third of the property. This stream will continue to collect surface water following development.
Other stormwater will be managed by utilizing biofiltration basin-type drainage management areas
(‘DMAs’) for stormwater Best Management Practices (‘BMPs’). Conceptual planning locates the basins
in the northwestern area of the property.
Figure 2-4 depicts the planned layout of the storm drain system.
Figure 2-4. Proposed Storm Drain System
(source: Latitude 33 2017)
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2.3 Below Grade Construction and Potential for Earthwork
2.3.1 Below Grade Construction
Based upon review of the design that is currently available, there is no indication of planning for below
grade construction of any scale (basements, subterranean garages, etc.). Adapting the residential
structures to the existing site grades may require that small (less than 5 feet height) embankments be
retained.
It is, of course, understood that construction of utilities, certain elements of stormwater BMPs, and related
infrastructure will require limited below grade construction.
2.3.2 Potential for Earthwork
NOVA estimates that requirements for earthwork will be limited. In review of planning that is currently
available, it appears that the new structures will be developed from approximately existing grade. There
is will be limited requirements for cutting and filling to adapt structures and drainage to existing site
grades.
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3.0 FIELD EXPLORATION AND LABORATORY TESTING
3.1 Overview
The field exploration by NOVA was completed on November 9, 2017. The field exploration consisted of
six engineering borings (referenced as B-1 through B-6) and four percolation test borings (referenced as
P-1 through P-4). The borings were drilled under the surveillance of a NOVA geologist by a specialty
subcontractor retained by NOVA.
Figure 3-1 depicts the location of the field work. Plate 1, provided immediately following the text of
this report provides a larger scale depiction of Figure 3-1.
Figure 3-1. Location of the Engineering and Percolation Test Borings
(source: adapted from Studio E Architects 2017)
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Soil samples recovered from the engineering borings were transferred to NOVA’s geotechnical laboratory
where a geotechnical engineer reviewed the soil samples and the field logs. Representative soil samples
were selected and tested in NOVA’s materials laboratory to check visual classifications and to determine
pertinent engineering properties.
3.2 Engineering Borings
3.2.1 General
The engineering borings were advanced by a truck-mounted drilling rig utilizing hollow stem auger
drilling equipment. Boring locations were determined in the field by the NOVA geologist. Elevations of
the ground surface at the boring locations were estimated. Table 3-1 provides an abstract of the
engineering borings.
Table 3-1. Abstract of the Engineering Borings
Boring
Reference
Approximate Ground
Surface Elevation
(feet, msl)
Total Depth
Below Ground
Surface (feet)
Depth to
Groundwater
(feet)
B-1 +80 21.5 n/e
B-2 +73 21.5 n/e
B-3 +68 21.5 n/e
B-4 +60 21.5 n/e
B-5 +58 36.5 33
B-6 +55 18 n/e
Notes:
1. ‘n/e’ indicates ‘groundwater not encountered’
2. B-6 terminated at 18 feet due to refusal on dense soils
3.2.2 Logging and Sampling
The borings were completed under the direction of a geologist from NOVA who directed sampling and
maintained a log of the subsurface materials that were encountered.
Both disturbed and relatively undisturbed samples were recovered from the borings, sampling of soils is
described below.
1. The Modified California sampler (‘ring sampler’, after ASTM D 3550) was driven using a 140-
pound hammer falling for 30 inches with a total penetration of 18 inches, recording blow counts
for each 6 inches of penetration.
2. The Standard Penetration Test sampler (‘SPT’, after ASTM D 1586) was driven in the same
manner as the ring sampler, recording blow counts in the same fashion. SPT blow counts for the
final 12 inches of penetration comprise the SPT ‘N’ value, an index of soil consistency.
3. Bulk samples were recovered from the upper 5 feet of the subsurface, providing composite
samples for testing of soil moisture and density relationships and corrosivity.
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Logs of the borings are provided in Appendix B. The group symbols for each soil type are indicated in
parentheses following the soil descriptions on the logs. The stratification lines designating the interfaces
between earth materials on the trench, boring logs and profiles are approximate; in-situ, the transitions
may be gradual.
3.2.3 Closure
Each boring was backfilled to the ground surface with bentonite chips and cuttings upon completion. The
area of each boring was restored as closely as possible to its approximate condition before drilling.
3.3 Percolation Testing
3.3.1 General
NOVA directed the excavation and construction of four (4) percolation test borings, following the
recommendations for percolation testing presented in the City of Chula Vista BMP Design Manual. The
locations of these borings are shown on Figure 3-1.
3.3.2 Drilling
Borings were drilled with a truck mounted 8-inch hollow stem auger to the level of the base of planned
storm water infiltration BMPs, five to six feet bgs. Field measurements were taken to confirm that the
borings were excavated to approximately 8-inches in diameter.
The borings were logged by a NOVA geologist, who observed and recorded exposed soil cuttings and the
boring conditions. Logs of the exploratory percolation test borings are provided in Appendix B.
3.3.3 Conversion to Percolation Wells
Once the test borings were drilled to the design depth, the borings were converted to percolation wells by
placing an approximately 2-inch layer of ¾-inch gravel on the bottom, then extending 3-inch diameter
Schedule 40 perforated PVC pipe to the ground surface. The ¾-inch gravel was used to fill the annular
space around the perforated pipe to at least 12-inches below existing finish grade to minimize the
potential of soil caving.
3.3.4 Percolation Testing
The percolation test holes were pre-soaked before testing and immediately prior to testing. The pre-soak
process consisted of filling the hole twice with water before testing. Water levels were recorded every 30
minutes for six hours (minimum of 12 readings), or until the water percolation stabilized after each
reading, the water level was raised to close to the previous water level to maintain a near constant head
before subsequent readings.
Table 3-2 (following page) abstracts the indications of the percolation testing.
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Table 3-2. Abstract of the Percolation Testing
Boring
Approx.
Elevation
(feet, msl)
Total
Depth
(feet)
Approximate
Percolation Test
Elev. (feet, msl)
Percolation
Rate (in/hour)2
Subsurface
Units Tested
1
P-1 +54 5 +49 0.24 Qa
P-2 +50 5 +45 0.48 Qa
P-3 +49 5 +44 0.72 Qa
P-4 +50 5 +45 0.48 Qa
Note: The referenced geologic unit is Alluvium (Qal).
3.3.5 Closure
At the conclusion of the percolation testing, the upper sections of the PVC pipe were removed and the
resulting holes backfilled with soil cuttings and patched to match the existing surfacing.
3.4 Geotechnical Laboratory Testing
3.4.1 General
Soil samples were returned to the laboratory where a geotechnical engineer reviewed the field logs and
classified each soil sample on the basis of texture and plasticity in accordance with the Unified Soil
Classification System (‘USCS,’ ASTM D2487). Representative soil samples were selected and tested in
NOVA’s materials laboratory to check visual classifications and to determine pertinent engineering
properties. The laboratory testing program included index testing on selected soil samples. Results of the
testing are presented in Appendix E.
3.4.2 Compaction
Near-surface soils removed from excavations may be suitable for reuse (see Section 6 for definition of
suitable soils). In order to address the potential that some soil could be replaced, compaction testing after
ASTM D 1557 was undertaken to establish the moisture-density relationship of these soils. The results of
the compaction testing are summarized in Table 3-3.
Table 3-3. Summary of the Compaction Testing, ASTM D 1557
Boring Sample
Depth (feet)
Soil
Description
Maximum Dry
Density (lb/ft3)
Optimum Moisture
Content (%)
B-1 0 to 5 Dark brown sandy silt 122.0 9.5
B-6 0 to 5 Dark brown sandy silt 128.5 8.7
3.4.3 Soil Gradation and Moisture
The visual classifications were further evaluated by performing moisture content and grain size testing.
Gradation testing was performed after ASTM D422. Table 3-4 (following page) provides a summary of
this testing.
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Table 3-4. Abstract of the Soil Gradation and Moisture Content Testing
Sample Reference As Sampled Percent Finer
than the U.S.
No 200 Sieve
Classification
after
ASTM D2488BoringDepth
(feet)
Natural
Moisture (%)
Dry Unit
Weight (pcf)
B-1 5 10 116
B-1 20 51 SM-ML
B-4 10 9 113
B-4 15 35 SM
B-5 5 11 116
B-5 35 22 SM
B-6 2.5 9 124
B-6 7.5 50 SM-ML
B-1 0 to 5 57 ML-SM
B-3 15 to 20 46 SM-ML
B-5 30 to 35 35 SM
B-6 0 to 5 50 SM-ML
P-1 0 to 5 51 ML-SM
P-2 0 to 5 51 ML-SM
P-3 0 to 5 49 SM-ML
P-4 0 to 5 52 ML-SM
Note: ‘Percent finer’ is percent by weight passing the U.S. # 200 sieve (0.074 mm), after ASTM D6913.
3.4.4 R-Value
The purpose of this test is to determine the suitability of prospective subgrade soils and road aggregates
for use in the pavement sections of roadways. The test is used by Caltrans for pavement design, replacing
the California Bearing Ratio (CBR) test.
The Resistance Value (R-value) test is a material stiffness test, demonstrating a material’s resistance to
deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure. A
saturated cylindrical soil sample is placed in a Hveem Stabilometer device and then compressed. The
stabilometer measures the horizontal pressure that is produced while the specimen is under compression.
A sample representative of soils from the upper five feet of Boring 3 was selected for this testing. Testing
after ASTM D 2844 indicated an R-value of 12, a value characteristic of R-values for silty soils. Design
for pavements should anticipate R ~ 12.
3.4.5 Plasticity and Expansion Potential
As is noted in Section 3.4.1 a geotechnical engineer reviewed the field logs and classified each soil
sample on the basis of texture and plasticity in accordance with the USCS. Based upon this review, it is
the judgment of NOVA that the soils at the site are predominantly cohesionless, with no expansion
potential. Based upon this judgment, no testing to determine plasticity (i.e., Atterberg Limits after ASTM
D 4318) or expansion potential (i.e., Expansion Index after ASTM D 4829).
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3.5 Corrosion Potential
A representative sample of the near-surface soils was sent to a chemical laboratory for testing to evaluate
the potential for soils to corrode embedded metals or concrete. Electrical resistivity, chloride content,
and pH level are all indicators of the soil’s tendency to corrode ferrous metals. High concentrations of
water-soluble sulfates can react with and damage concrete.
The chemical testing was performed by Clarkson Laboratory and Supply, Inc. The results of the testing
are tabulated on Table 3-5.
Table 3-5. Summary of the Corrosivity Testing
Parameter Units Boring 3
0 to 5 Feet
pH Standard 7.8
Resistivity Ohm-cm 1100
Water Soluble Sulfate ppm 21
Water Soluble Chloride ppm 87
The indications of the above testing are discussed in more detail in Section 6.
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4.0 SITE CONDITIONS
4.1 Geologic and Seismic Setting
4.1.1 Regional
The project area is located in the coastal portion of the Peninsular Range geomorphic province. This
geomorphic province encompasses an area that extends approximately 900 miles from the Transverse
Ranges and the Los Angeles Basin south to the southern tip of Baja California. The province varies in
width from approximately 30 to 100 miles.
This area of the Province has undergone several episodes of marine inundation and subsequent marine
regression (coastline changes) throughout the last 54 million years. These events have resulted in the
deposition of a thick sequence of marine and nonmarine sedimentary rocks on the basement igneous rocks
of the Southern California Batholith and metamorphic rocks.
Gradual emergence of the region from the sea occurred in Pleistocene time, and numerous wave-cut
platforms, most of which were covered by relatively thin marine and nonmarine terrace deposits, formed
as the sea receded from the land. Accelerated fluvial erosion during periods of heavy rainfall, along with
the lowering of base sea level during Quaternary times, resulted in the rolling hills, mesas, and deeply
incised canyons which characterize the landforms in western San Diego County.
4.1.2 Site Specific
The site is situated within the coastal plain zone of the Peninsular Ranges geomorphic province. The
geology of the area is controlled by both alluvial and marine influences. This plain is underlain by near-
shore marine sedimentary rocks deposited at various intervals from the late-Mesozoic through Quaternary
ages. The Coastal Plain increases in elevation from west to east across marine terrace surfaces uplifted
during Pleistocene time. Sedimentary rocks consist of sandstones, siltstones, and claystones that were
deposited during the Cretaceous, Tertiary, and Quaternary periods.
Geologic units encountered at this site include alluvium and Very Old Paralic deposits. Figure 4-1
(following page) depicts the geology of the site area from which it can be seen that Very Old Paralic
deposits (Qvop) are mapped to occur widely in this area of Chula Vista.
The Very Old Paralic deposits are shallow marine and nonmarine (talus and slopewash) terrace deposits
of Pleistocene age. The Paralics were deposited on a currently-raised 6 mile-wide wavecut platform.
Soils of this unit are typically consolidated, light brown to reddish brown, clean to silty, medium- to
coarse-grained sand and gravels with localized interbeds of clayey sand and sandy clay (i.e., localized
back-beach lagoonal deposits).
The paralics occur widely, found from the International Border to northern Carlsbad and comprising the
dominant near-surface geologic formation in much of San Diego. The unit ranges to 65 feet in thickness,
but is generally less than 50 feet in thickness.
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Figure 4-1. Geologic Mapping of the Site Vicinity
4.2 Site Specific Conditions
4.2.1 Surface
As is evident by review of the aerial photo provided as Figure 2-1, the site area is currently undeveloped.
Figure 4-2 (following page) provides a view of the site depicting surface conditions. As may be seen by
review of this graphic, the site is cleared and covered by light grasses.
The ground surface slopes downward from east to west, declining from an average elevation of about +80
feet msl at the east to about +50 feet msl at the western end. This elevation differential occurs over a
distance of about 700 feet, a surface gradient of about 4%. Relatively steeper embankments rim the site
to the south and east.
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Figure 4-2. Site View from the East Along Vista Drive
4.2.2 Subsurface
The borings and test trenches indicate the site is covered by a thin veneer of fill below which lies
naturally occurring dense/stiff sands and clays. For the purposes of this report, the subsurface may be
considered to occur as the sequence of soil units described below.
x Unit 1, Alluvium (Qa). The site is overlain by alluvium, predominantly silty and sandy mix of
soils of medium dense to dense consistency. This unit ranges from 5 feet to 20 feet in thickness.
x Unit 2, Paralics. The alluvium material is underlain by silty and sandy soils of the Very Old
Paralic formation (Qvop). These materials are characteristically sandy and dense to very dense
consistency.
4.2.3 Groundwater
Static
Groundwater is expected to first occur below a depth of 30 feet, below about El +25 feet msl.
Perched
Infiltrating storm water from prolonged wet periods can ‘perch’ atop localized zones of lower
permeability soil that exist above the static groundwater level. Localized perched groundwater
conditions may also develop once site development is complete and landscape irrigation
commences.
No perched groundwater was observed during drilling of the engineering borings.
4.2.4 Surface Water
No surface water was evident on the site at the time of NOVA’s work.
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An ephemeral stream crosses the site, flowing approximately south to north on the western one-third of
the site. The approximate alignment and limits of this drainage feature are evident on a 2010 aerial photo,
reproduced as Figure 4-3.
Figure 4-3. Alignment and Limits of the Ephemeral Stream
NOVA did not observe any other visual evidence of seeps, springs, erosion, staining, discoloration, etc.
that would indicate the occurrence of surface water.
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5.0 REVIEW OF GEOLOGIC HAZARDS
5.1 Overview
This section provides a review of soil and geologic-related hazards common to this region of California,
considering each for its potential to affect the planned development.
The primary hazard identified by this review is the risk for moderate-to-severe ground shaking in
response to a large-magnitude earthquake during the lifetime of the planned development. While there is
no risk of liquefaction or related seismic phenomena, strong ground motion could affect the site. This
circumstance is common to all civil works in this area of California.
The following subsections address these and other potential soil and geologic hazards.
5.2 Geologic Hazards
5.2.1 Strong Ground Motion
The site is not located within a currently designated Alquist-Priolo Earthquake Zone (Hart and Bryant,
2007). No known active faults are mapped on the site area. The nearest known active faults are faults
within the Rose Canyon fault system, located approximately 3 miles west of the site. This system has the
potential to be a source of strong ground motion. The seismicity of the site was evaluated utilizing a
web-based analytical tool provided by the USGS. This evaluation shows the site may be subjected to a
Magnitude 7 seismic event, with a corresponding risk-based Peak Ground Acceleration (PGAM) of PGAM
~ 0.43 g.
No evidence of faulting was observed during NOVA’s geologic reconnaissance of the site. Geologic
mapping shows a fault mapped through or very close to the site. This fault is Quaternary in age, or
approximately 1 to 2 million years old. As such, it is NOVA’s professional opinion that this indicates
that the mapped fault is an inactive fault. Because of the lack of known active faults on the site, the
potential for surface rupture at the site is considered low. Shallow ground rupture due to shaking from
distant seismic events is not considered a significant hazard, although it is a possibility at any site.
Figure 5-1 (following page) maps faults in the site vicinity.
5.2.2 Landslide
As used herein, ‘landslide’ describes downslope displacement of a mass of rock, soil, and/or debris by
sliding, flowing, or falling. Such mass earth movements are greater than about 10 feet thick and larger
than 300 feet across. Landslides typically include cohesive block glides and disrupted slumps that are
formed by translation or rotation of the slope materials along one or more slip surfaces.
The causes of classic landslides start with a preexisting condition- characteristically, a plane of weak soil
or rock- inherent within the rock or soil mass. Thereafter, movement may be precipitated by earthquakes,
wet weather, and changes to the structural or loading conditions on a slope (e.g., by erosion, cutting,
filling, release of water from broken pipes, etc.).
In consideration of the relatively level ground at and around the site, NOVA considers the landslide
hazard at the site to be ‘negligible’ for the site and the surrounding area.
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Figure 5-1. Faulting in the Site Vicinity
5.3 Soil Hazards
5.3.1 Embankment Stability
As used herein, ‘embankment stability’ is intended to mean the safety of localized natural or man-made
embankments against failure. Unlike landslides described above, embankment stability can include
smaller scale slope failures such as erosion-related washouts and more subtle, less evident processes such
as soil creep.
No new slopes are planned as part of the future site development. However, as is discussed in Section 4,
the site is rimmed by ascending slopes to the south and east. Adaptation of the development to the slopes
may require the use of retaining walls to ensure embankment stability.
Similarly, the site is bounded by descending slopes to the north. Adaptation of developing infrastructure
to this condition will require additional consideration/evaluation of embankment stability.
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5.3.2 Seismic
Liquefaction
‘Liquefaction’ refers to the loss of soil strength during a seismic event. The phenomenon is
observed in areas that include geologically ‘younger’ soils (i.e., soils of Holocene age), shallow
water table (less than about 60 feet depth), and cohesionless (i.e., sandy and silty) soils of looser
consistency. The seismic ground motions increase soil water pressures, decreasing grain-to-grain
contact among the soil particles, which causes the soils to lose strength.
Resistance of a soil mass to liquefaction increases with increasing density, plasticity (associated
with clay-sized particles), geologic age, cementation, and stress history. The stiff/dense and
geologically ‘older’ subsurface units at this site have no potential for liquefaction.
Seismically Induced Settlement
Apart from liquefaction, a strong seismic event can induce settlement within loose to moderately
dense, unsaturated granular soils. The cohesionless sandy soils of both Unit 1 and Unit 2 are
sufficiently dense and finer grained that these soils will not be prone to seismic settlement.
Lateral Spreading
Lateral spreading is a phenomenon in which large blocks of intact, non-liquefied soil move
downslope on a liquefied soil layer. Lateral spreading is often a regional event. For lateral
spreading to occur, a liquefiable soil zone must be laterally continuous and unconstrained, free to
move along sloping ground. Due to the absence of a potential for liquefaction and relatively flat
surrounding topography, there is no potential for lateral spreading.
5.3.3 Expansive Soil
Expansive soils are characterized by their ability to undergo significant volume changes (shrinking or
swelling) due to variations in moisture content¸ the magnitude of which is related to both clay content and
plasticity index. These volume changes can be damaging to structures. Nationally, the annual value of
real estate damage caused by expansive soils is exceeded only by that caused by termites. The
encountered soils are expected to possess a low expansion potential.
5.3.4 Hydro-Collapsible Soils
Hydro-collapsible soils are common in the arid climates of the western United States in specific
depositional environments- principally, in areas of young alluvial fans, debris flow sediments, and loess
(wind-blown sediment) deposits. These soils are characterized by low in situ density, low moisture
contents, and relatively high unwetted strength. The soil grains of hydro-collapsible soils were initially
deposited in a loose state (i.e., high initial ‘void ratio‘) and thereafter lightly bonded by water sensitive
binding agents (e.g., clay particles, low-grade cementation, etc.). While relatively strong in a dry state,
the introduction of water into these soils causes the binding agents to fail. Destruction of the
bonds/binding causes relatively rapid densification and volume loss (collapse) of the soil. This change is
manifested at the ground surface as subsidence or settlement. Ground settlements from the wetting can be
damaging to structures and civil works. Human activities that can facilitate soil collapse include
irrigation, water impoundment, changes to the natural drainage, disposal of wastewater, etc.
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The consistency and geologic age of the Unit 1 alluvium and the Unit 2 Paralics is such that these soils
are not potentially hydro-collapsible.
5.3.5 Corrosive Soils
Chemical testing of the near-surface soils indicates the soils contain low concentrations of soluble sulfates
and chlorides. These soils will not be corrosive to embedded concrete and metals. Section 6 addresses
this consideration in more detail.
5.4 Other Hazards
5.4.1 Flood
The site is located within a FEMA-designated flood zone, FEMA Panel Nos.06073C1914G and
06073C1918G, effective on 05/16/2012. Most of the site area is designated “Zone X,” an area of minimal
flood hazard. However, the northwestern portion of the site is identified to include a 0.2% annual chance
of flooding. Figure 5-2 reproduces flood mapping by FEMA of the site area.
Figure 5-2. Flood Mapping of the Site
(source: FEMA Panel Nos.06073C1914G and 06073C1918G, effective on 05/16/2012)
5.4.2 Tsunami
Tsunami describes a series of fast-moving, long period ocean waves caused by earthquakes or volcanic
eruptions. The California Geological Survey Tsunami Inundation Map, National City Quadrangle (2009,
show that the site is not within a tsunami inundation area.
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5.4.3 Seiche
Seiches are standing waves that develop in an enclosed or partially enclosed body of water such as lakes
or reservoirs. Harbors or inlets can also develop seiches. Most commonly caused by strong winds and
rapid atmospheric pressure changes, seiches can be affected by seismic events and tsunamis.
The site is not located near a body of water that could generate a seiche.
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6.0 EARTHWORK AND FOUNDATIONS
6.1 Overview
6.1.1 General
Based upon the indications of the field and laboratory data developed for this investigation, as well as
review of previously developed subsurface information, it is the opinion of NOVA that the site is suitable
for development of the planned structure on shallow foundations provided the geotechnical
recommendations described herein are followed.
As is discussed in Section 5, the planned structures may experience strong ground motions associated
with a large magnitude earthquake. This hazard is common to all civil development in this area of
California. Section 6.2 addresses seismic design parameters.
6.1.2 Review and Surveillance
The subsections following provide geotechnical recommendations for the planned development as it is
now understood. It is intended that these recommendations provide sufficient geotechnical information to
develop the project in general accordance with 2016 California Building Code (CBC) requirements.
NOVA should be given the opportunity to review the grading plan, foundation plan, and geotechnical-
related specifications as they become available to confirm that the recommendations presented in this
report have been incorporated into the plans prepared for the project. All earthwork related to site and
foundation preparation should be completed under the observation of NOVA.
6.2 Seismic Design Parameters
6.2.1 Site Class
The site-specific data used to determine the Site Class typically includes borings drilled to refusal
materials to determine Standard Penetration resistances (N-values). The depth of soil information
available for this site is limited, such that the site is classified as Site Class D per ASCE 7 (Table 20.3-1).
6.2.2 Seismic Design Parameters
Table 6-1 (following page) provides seismic design parameters for the site in accordance with 2016 CBC
and mapped spectral acceleration parameters.
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Table 6-1. Seismic Design Parameters, ASCE 7-10
Parameter Value
Site Soil Class D
Site Latitude (decimal degrees)32.64649
Site Longitude (decimal degrees)-117.06346
Site Coefficient, Fa 1.124
Site Coefficient, Fv 1.684
Mapped Short Period Spectral Acceleration, SS 0.940 g
Mapped One-Second Period Spectral Acceleration, S1 0.358 g
Short Period Spectral Acceleration Adjusted For Site Class, SMS 1.057 g
One-Second Period Spectral Acceleration Adjusted For Site Class, SM1 0.603 g
Design Short Period Spectral Acceleration, SDS 0.705 g
Design One-Second Period Spectral Acceleration, SD1 0.402 g
Source: U.S. Seismic Design Maps, found at http://earthquake.usgs.gov/designmaps/us/application.php
6.3 Corrosivity and Sulfates
6.3.1 General
Electrical resistivity, chloride content, and pH level are all indicators of the soil’s tendency to corrode
ferrous metals. These chemical tests were performed on a representative sample of the near-surface soils
by Clarkson Laboratory and Supply, Inc. Records of this testing are provided in Appendix E.
The results of the testing are provided in Section 3 and again tabulated on Table 6-2.
Table 6-2. Summary of Corrosivity Testing of the Near Surface Soil
Parameter Units Value
pH standard unit 7.8
Resistivity Ohm-cm 1100
Water Soluble Chloride ppm 21
Water Soluble Sulfate ppm 87
6.3.2 Metals
Caltrans considers a soil to be corrosive if one or more of the following conditions exist for representative
soil and/or water samples taken at the site:
x chloride concentration is 500 parts per million (ppm) or greater;
x sulfate concentration is 2,000 ppm (0.2%) or greater; or,
x the pH is 5.5 or less.
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Based on the Caltrans criteria, the on-site soils would not be considered corrosive to buried metals.
Appendix E provides records of the chemical testing that include estimates of the life expectancy of
buried metal culverts of varying gauge.
In addition to the above parameters, the risk of soil corrosivity buried metals is considered by
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only in unsaturated soils. Corrosion of buried metal is an electrochemical process in which the amount of
metal loss due to corrosion is directly proportional to the flow of DC electrical current from the metal into
the soil. As the resistivity of the soil decreases, the corrosivity generally increases. A common qualitative
correlation (cited in Romanoff 1989, NACE 2007) between soil resistivity and corrosivity to ferrous
metals is tabulated below.
Table 6-3. Soil Resistivity and Corrosion Potential
Minimum Soil
Resistivity (ȍ-cm)
Qualitative Corrosion
Potential
0 to 2,000 Severe
2,000 to 10,000 Moderate
10,000 to 30,000 Mild
Over 30,000 Not Likely
Despite the relatively benign environment for corrosivity indicated by pH and water-soluble chlorides, the
resistivity testing suggests that design should consider that the soils may be moderately corrosive to
embedded ferrous metals.
Typical recommendations for mitigation of such corrosion potential in embedded ferrous metals include:
x a high-quality protective coating such as an 18-mil plastic tape, extruded polyethylene, coal tar
enamel, or Portland cement mortar;
x electrical isolation from above grade ferrous metals and other dissimilar metals by means of
dielectric fittings in utilities and exposed metal structures breaking grade; and,
x steel and wire reinforcement within concrete having contact with the site soils should have at
least 2 inches of concrete cover.
If extremely sensitive ferrous metals are expected to be placed in contact with the site soils, it may be
desirable to consult a corrosion specialist regarding choosing the construction materials and/or protection
design for the objects of concern.
6.3.3 Sulfates and Concrete
The soil sample tested in this evaluation indicated water-soluble sulfate (SO4) content of 87 parts per
million (‘ppm,’ 0.009 % by weight). The American Concrete Institute (ACI) 318-08 considers soil with
this concentration of SO4 to have no potential to for sulfate attack to embedded concrete (i.e., Exposure
Class ‘S0’). Table 6-4 (following page) reproduces the ACI guidance.
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Table 6-4. Exposure Categories and Requirements for Water-Soluble Sulfates
Exposure
Category Class Water-Soluble Sulfate
(SO4) In Soil
(percent by weight)
Cement Type
(ASTM C150)
Max. Water-
Cement Ratio
Min. f’c
(psi)
Not Applicable S0 SO4 < 0.10 - - -
Moderate S1 624 < 0.20 II 0.50 4,000
Severe S2 624 V 0.45 4,500
Very severe S3 SO4 > 2.0 V + pozzolan 0.45 4,500
Adapted from: ACI 318-08, Building Code Requirements for Structural Concrete
6.3.4 Limitations
Testing to determine several chemical parameters that indicate a potential for soils to be corrosive to
construction materials are traditionally completed by the Geotechnical Engineer, comparing test results
with a variety of indices regarding corrosion potential.
Like most geotechnical consultants, NOVA does not practice in the field of corrosion protection, since
this is not specifically a geotechnical issue. Should you require more information, a specialty corrosion
consultant should be retained to address these issues.
6.4 Site Preparation and Earthwork
6.4.1 Establish Erosion and Sedimentation Control
Construction-related erosion and sedimentation must be controlled in accordance with Best Management
Practices and City of San Diego requirements. These controls should be established at the outset of site
disturbance.
6.4.2 Clearing and Grubbing
Before proceeding with construction, all vegetation, root systems, topsoil, refuse and other deleterious
nonsoil materials should be stripped from construction areas.
Underground utilities within the footprint of the proposed structures should be grouted in place or
removed. Clearing, include the removal of any abandoned utilities, should be extended a minimum of 5
feet beyond the building and pavement limits.
Stripped materials consisting of vegetation and organic materials should be wasted from the site, or used
in landscaping non-structural areas
6.4.3 Grading for Foundations
Foundations- either ground supported slabs or footings- may be supported at grade on Unit 1 alluvium or
Unit 2 paralics prepared as described in this section. Preparation of the subgrade for ground supported
slabs should include the step-wise series of actions described below.
1. Excavation. Soils should be excavated to a minimum of five feet below finish pad grade or three
feet below the bottom of footings, whichever is greater. The removals should extend to at least
three feet laterally beyond the structure footprint. The excavated soils should be staged near the
excavation for moisture conditioning and subsequent reuse.
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2. Redensification/Proof Rolling. Prior to replacement, the soils disturbed by excavation should be
examined to identify any localized soft, yielding or otherwise unsuitable materials by a
Geotechnical Engineer from NOVA. Areas at the bottom of the removal area that are disturbed
by excavation should be re-densified to 90% relative compaction after ASTM D1557 (the
‘modified Proctor’). Thereafter, the area should be proof rolled with a heavily loaded wheeled
vehicle (for example, a loaded dump truck) to identify any remaining loose areas.
3. Soil Replacement. Excavated soils that are free of organics may be replaced following moisture
conditioning to at least 2% of the optimum moisture content then recompacted to at least 90%
relative compaction after ASTM D1557 (the ‘Modified Proctor’). The moisture conditioned soil
should be replaced in loose lifts then compacted by equipment suitable for the lift thickness and
soil type. The loose lifts of soil should not exceed 10-inches.
4. Select Replacement Soil. In the event that the excavated soils prove unsuitable for use or a
shortage of these soils occurs, the soil replacement may be completed by use of a Select Fill.
Such soil should consist of a well-graded, low expansivity soil (EI < 50), with at least 40% fines
and no particle size greater than 2”. Most of Unit 1 and Unit 2 soil now found on-site meet these
criteria.
The Select Fill should be moisture-conditioned to at least 2 percent over the optimum moisture
content and densified to at least 90% relative compaction after ASTM D1557. The Select Fill
should be placed in loose lifts, then compacted by equipment suitable for the lift thickness and
soil type. The loose lifts of soil should not exceed 10-inches.
5. Timely Foundation Construction. Foundations should be constructed as soon as possible
following subgrade approval. The Contractor should be responsible for maintaining the subgrade
in its approved condition (i.e., free of water, debris, etc.) until the foundation is constructed.
6.4.4 Remedial Grading for Flatwork
Non-structural areas outside of building pads that include sidewalks and other flatwork, etc., should be
over-excavated a minimum of 24-inches below existing grade or finished subgrade, whichever is deeper,
and be replaced with either moisture conditioned Unit 1 soil or imported Select Fill. The bottom of the
removal area should be re-densified to 90% relative compaction after ASTM D1557 (the ‘modified
Proctor’).
Depending on the observed condition of the existing soils, deeper over-excavation may be required in
some areas. The over-excavation should extend beyond the proposed improvements a horizontal distance
of at least two feet.
6.5 Shallow Foundations
6.5.1 Bearing Unit
Spread or continuous footings can be used to support the new structures. These foundations should bear
on compacted fill soils.
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6.5.2 Minimum Dimensions and Reinforcing
Continuous footings should be at least 24 inches wide and have a minimum embedment of 24 inches
below lowest adjacent grade. Isolated square or rectangular footings should be a minimum of 36 inches
wide, embedded at least 24 inches below surrounding grade.
It is recommended that all foundation elements, including any grade beams, be reinforced top and bottom.
The actual reinforcement should be designed by the Structural Engineer.
6.5.3 Allowable Contact Stress
Continuous and isolated footings constructed as described in the preceding sections may be designed
using an allowable (net) contact stress of 2,500 pounds per square foot (psf). An allowable increase of
500 psf for each additional 12 inches in depth may be utilized, if desired.
In no case should the maximum allowable contact stress should be greater than 4,000 psf. The maximum
bearing value applies to combined dead and sustained live loads (DL + LL). The allowable bearing
pressure may be increased by one-third when considering transient live loads, including seismic and wind
forces.
6.5.4 Lateral Resistance
Resistance to lateral loads will be provided by a combination of (i) friction between the soils and
foundation interface; and, (ii) passive pressure acting against the vertical portion of the footings. Passive
pressure may be calculated at 250 psf per foot of depth. A frictional coefficient of 0.35 may be used. No
reduction is necessary when combining frictional and passive resistance.
6.5.5 Settlement
Structure supported on shallow foundations as recommended above will settle on the order of 0.5 inch or
less, with about 80% of this settlement occurring during the construction period.
The differential settlement between adjacent columns is estimated on the order of ½ inch over a
horizontal distance of 40 feet. The estimated seismic settlement (on the order of a ½ inch or less, as is
discussed in Section 5) would occur in addition to this movement.
6.5.6 Footing Construction and Inspection
Foundation excavations be cleaned of loose material and observed by a qualified Geotechnical Engineer
or Engineering Geologist prior to placing steel or concrete to verify soil conditions exposed at the base of
the excavations.
6.6 Ground Supported Slabs
6.6.1 Conventionally Reinforced Slab-on-Grade
Conventionally reinforced on-grade concrete slabs may be designed using a modulus of subgrade reaction
of 80 pounds per cubic inch (80 pci) provided the subgrade is prepared as described in Section 6.4.
The actual slab thickness and reinforcement should be designed by the Structural Engineer. NOVA
recommends the slab be a minimum 5 inches thick, reinforced by at least #3 bars placed at 16 inches on
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center each way within the middle third of the slabs by supporting the steel on chairs or concrete blocks
("dobies").
Designed as described above, slab foundations will settle less than ¾ inch maximum with angular
distortion due to differential settlement of unequally loaded areas less than one in 400. About 80% of
foundation movement will occur during construction, such that post-construction settlement should be
small enough to be imperceptible.
Despite the expected low building movements, minor cracking of slab concrete after curing due to drying
and shrinkage is normal and can occur. Cracking is aggravated by a variety of factors, including high
water/cement ratio, high concrete temperature at the time of placement, small nominal aggregate size, and
rapid moisture loss due during curing. The use of low-slump concrete or low water/cement ratios can
reduce the potential for shrinkage cracking. To reduce the potential for excessive cracking, concrete
slabs-on-grade should be provided with construction or ‘weakened plane’ joints at frequent intervals.
Joints should be laid out to form approximately square panels.
6.6.2 Slab Setback from Slopes
Descending slopes bound the site to the north, locally as steep as about 2.5:1 (H:V). In review of aerial
photographs of the site dating to 1994, NOVA observed no indications of instability of the embankments
in this area.
Foundations for the apartment structures should be set back from descending slopes as described below:
x a minimum of 5 feet from the crest of any descending slope 4:1 (H:V) or flatter; and
x a minimum of 10 feet from the crest of any descending slope steeper than 4:1 (H:V).
6.6.3 Slope Maintenance
The existing site slopes will be stable, but only with proper maintenance. Design should take care to not
change the surface water environment in or around the drainage canyon. This should include care to
control surface water drainage over the slopes and to vegetate slopes to limit erosion. Absent such
protection, surficial instability or "sloughing" and “rilling erosion” will occur. If such smaller-scale
losses of ground occur repairs should be affected to avoid larger scale loss of ground.
6.6.4 Moisture Barrier
Industry Design Guidance
NOVA recommends that any moisture barrier be designed in accordance with ACI Publication
302.1R-15, “Guide to Concrete Floor and Slab Construction.”
Capillary Break and Vapor Membrane
Ground supported slabs that support moisture-sensitive floor coverings or equipment may be
protected by an underslab moisture barrier. Such barriers normally include two components, as
described below
1. Capillary Break. A “capillary break” consisting of a 4-inch thick layer of
compacted, well-graded gravel or crushed stone should be placed below the
floor slab. This porous fill should be clean coarse sand or sound, durable gravel
with not more than 5 percent coarser than the 1-inch sieve or more than 10
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percent finer than the No. 4 sieve, such as AASHTO Coarse Aggregate No. 57.
2. Vapor Membrane. A minimum 15-mil polyethylene membrane, or similarly-
rated vapor barrier, should be placed over the porous fill to preclude floor
dampness. Membranes set below floor slabs should be rugged enough to
withstand construction. NOVA recommends that a minimum 15 mil low
permeance vapor membrane be used. For example, Carlisle-CCW produces the
Blackline 400® underslab, vapor and air barrier, a 15-mil low-density
polyethylene (LDPE) rated at 0.012 perms after ASTM E 96.
Limitations of This recommendation
Recommendation for moisture barriers are traditionally included with geotechnical foundation
recommendations, though these requirements are primarily the responsibility of the Structural
Engineer or Architect. NOVA does not practice in the field of moisture vapor transmission
evaluation, since this is not specifically a geotechnical issue. A specialty consultant would
provide recommendations for mitigation of potential adverse impact of moisture vapor
transmission on various components of the structures, as deemed appropriate.
6.7 Control of Drainage Around Structures
6.7.1 General
Geotechnical, civil, structural, architectural and landscaping design for the areas around foundations must
be undertaken with a view to the maintenance of an environment that encourages constant moisture
conditions in the soils following construction. Roof and surface drainage, landscaping, and utility
connections must be designed to limit infiltration and/or releases of moisture beneath or around
structures. This care should, at a minimum, include the actions described in the following subsections.
6.7.2 Landscaping
Landscaping adjacent to the structures should be limited. No new trees should be planted. If used, trees
should be planted the greater of (i) 15 feet away from foundations; or (ii) 1.5 times its mature height away
from foundations.
Do not plant flowers or shrubs closer than five (5) feet from foundations. Planters and other surface
features which could retain water in areas adjacent to the buildings should be sealed or eliminated.
Sprinkler systems should not be installed within 5 feet of foundations or floor slabs.
If trees are planted at locations that do not conform with the above, this action would be undertaken at the
Designer’s/Owner’s sole risk. In such an event, the risk of such planting can perhaps be limited by
utilizing root barriers, drought-resistant trees (to limit the need for watering) or trees with relatively
shallower root systems.
6.7.3 Drainage
Rainfall to roofs should be collected in gutters and discharged in a controlled manner through downspouts
designed to drain away from foundations. Downspouts, roof drains or scuppers should discharge into
splash blocks to slabs or paving sloped away from buildings.
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6.7.4 Surface Grades
In areas where sidewalks or paving do not immediately adjoin the structure, protective slopes should be
provided with a minimum grade of approximately 3 percent for at least 10 feet from perimeter walls.
A minimum gradient of 1 percent is recommended in hardscape areas. In earth areas, a minimum gradient
of 5 percent away from the structure for a distance of at least 10 feet should be provided. Earth swales
should have a minimum gradient of 2 percent. Storm water should be directed to approved drainage
facilities. Proper surface and subsurface drainage will be required to minimize the potential for surface
water to seep to the level of the bearing soils under the foundations, pavements, and flatwork.
6.7.5 Backfills
In order to reduce the possibility of moisture infiltration, backfill against foundation elements, exterior
walls, and in utility and sprinkler line trenches should be with well compacted, non-expansive, low
permeability soil that is free of all construction debris.
6.7.6 Utilities
Design for Differential Movement
Underground piping within or near structures should be designed with flexible couplings to
accommodate both ground and slab movement, so that minor deviations in alignment do not
result in breakage or distress. Utility knockouts should be oversized to accommodate the
potential for differential movements.
Backfill Above Utilities.
Excavations for utility lines which extend under or near structural areas should be properly
backfilled and compacted. Utilities should be bedded and backfilled with approved granular soil
to a depth of at least one foot over the pipe. This backfill should be uniformly watered and
compacted to a firm condition for pipe support. The remainder of the backfill should be low
permeability clayey soils, moisture-conditioned and compacted to at least 90%.
6.8 Retaining Walls
6.8.1 General
As is discussed in Section 2, only conceptual design information is currently available. Review of this
information indicates that smaller retaining walls may be employed near ascending slopes.
The following subsections provide guidance for design of cantilevered retaining walls should planning
change and such retaining structures be employed.
6.8.2 Shallow Foundations
Retaining walls should be developed on ground prepared in accordance with the criteria provided in
Section 6.4. Continuous shallow foundations may be designed in accordance with the criteria provided in
Section 6.5.
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6.8.3 Lateral Earth Pressures
Design may include smaller (perhaps 6 feet to 10 feet tall) cantilevered, conventionally reinforced
concrete retaining walls. This section provides recommendations for wall pressures for those walls.
Lateral earth pressures for wall design are provided on Table 6-5 (following page) as equivalent fluid
weights, in psf/foot of wall height or pounds per cubic foot (pcf). These values do not contain a factor of
safety.
Table 6-5. Lateral Earth Pressures
Loading Condition
Equivalent Fluid Density (pcf) for
Approved ‘Native’ Backfill Notes A, B
Level Backfill 2:1 Backfill
Sloping Upwards
Active (wall movement allowed) 35 60
“At Rest” (no wall movement) 65 100
‘Passive” (wall movement toward the soils) 260 220
Note A: ‘native’ means site-sourced soil with EI < 50 after ASTM D4546.
Note B: assumes wall includes appropriate drainage.
6.8.4 Foundation Uplift
A soil unit weight of 125 pcf may be assumed for calculating the weight of soil over the wall footing.
6.8.5 Resistance to Lateral Loads
Lateral loads to wall foundations will be resisted by a combination of frictional and passive resistance as
described below.
x Frictional Resistance. A coefficient of friction of 0.35 between the soil and base of the footing.
x Passive Resistance. Passive soil pressure against the face of footings or shear keys will
accumulate at an equivalent fluid weight of 250 pounds per cubic foot (pcf). The upper 12 inches
of material in areas not protected by floor slabs or pavement should not be included in
calculations of passive resistance.
6.8.6 Wall Drainage
The above recommendations assume a wall drainage panel or a properly compacted granular free-
draining backfill material (EI <50).
The use of drainage openings through the base of the wall (weep holes) is not recommended where the
seepage could be a nuisance or otherwise adversely affect the property adjacent to the base of the wall.
6.8.7 Seismic
The lateral seismic pressure acting on a cantilevered retaining wall should be applied as an inverted
triangle with a magnitude of 11H, where H is the free height of the wall. The resultant dynamic thrust
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acts at a distance of 0.6H above the base of the wall. This equation applies to level backfill and walls that
retain no more than 15 feet of soil.
6.9 Elevator Pits
Though detailed planning is not available, it is possible that structures may include elevators, such that
elevator pits may be necessary.
Walls for an elevator pit should be designed in accordance with the recommendations provided in Section
6.7 for retaining walls. The elevator slab and related retaining wall footings will derive support from the
formational soils that will be exposed in an excavation for the elevator pit.
Design for the elevator pit walls should add care that considers the circumstances and conditions
described below.
1. Wall Yield. NOVA expects that proper function of the elevator pit should not allow yielding of
the elevator pit walls. As such, walls should be designed to resist ‘at rest’ lateral soil pressures
plus the surcharge of any structures or foundations surrounding the elevator pit.
2. Construction. By virtue of a usual location near the center of the structure, the need for special
equipment, and the likelihood that elevator pit construction will precede much of the construction
around it, design of elevator pit walls should include consideration for surcharge conditions that
will occur during construction. Such conditions may include, but not be limited to, surcharges
from vehicle traffic and sloping ground above and around the walls.
3. Moisture. Consideration should be given to passive side waterproofing or damp proofing to
prevent moisture accumulation inside the elevator pit.
4. Piston. If the elevator pit includes a plunger-type elevator piston, a deeper drilled excavation may
be required. NOVA should be consulted regarding recommendations for development of a
plunger-type elevator piston.
6.10 Temporary Slopes
Temporary slopes may be required for excavations during grading. All temporary excavations should
comply with local safety ordinances. The safety of all excavations is solely the responsibility of the
Contractor and should be evaluated during construction as the excavation progresses.
Based on the data interpreted from the borings, the design of temporary slopes may assume California
Occupational Safety and Health Administration (Cal/OSHA) Soil Type C for planning purposes.
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7.0 STORMWATER INFILTRATION
7.1 Overview
Based upon the indications of the field exploration and laboratory testing reported herein, NOVA has
evaluated the site as abstracted below after guidance contained in the County of San Diego BMP Design
Manual (hereafter, ‘the BMP Manual’), which is been adopted by the City of Chula Vista.
Section 3.3 provides a description of the field work undertaken to complete the testing. Figure 3-1
depicts the location of the testing. This section provides the results of that testing and related
recommendations for management of stormwater in conformance with the BMP Manual. The discussion
provides NOVA’s assessment of the feasibility of stormwater infiltration BMPs utilizing the information
developed by the field exploration described in Section 3, as well as other elements of the site assessment.
7.2 Infiltration Rates
7.2.1 General
The percolation rate of a soil profile is not the same as its infiltration rate (‘I’). Therefore, the
measured/calculated field percolation rate was converted to an estimated infiltration rate utilizing the
Porchet Method in accordance with guidance contained in the BMP Manual.
Table 7-1 provides a summary of the infiltration rates determined by the percolation testing.
Table 7-1. Infiltration Rates Determined by Percolation Testing
Boring
Approximate
Ground Elevation
(feet, msl)
Depth of
Test
(feet)
Approximate
Test Elevation
(feet, msl)
Infiltration
Rate
(inches/hour)
Design
Infiltration Rate
(in/hour, F=2*)
P-1 +54 5 +49 0.00 0.00
P-2 +50 5 +45 0.01 0.00
P-3 +49 5 +44 0.01 0.01
P-4 +50 5 +45 0.01 0.00
Notes: (1) ‘F’ indicates ‘Factor of Safety’ (2) elevations are approximate.
7.2.2 Design Infiltration Rate
In consideration of the nature and variability of subsurface materials, as well as the natural tendency of
infiltration structures to become less efficient with time, the infiltration rates measured in the testing
should be modified to use at least a factor of safety (F) of F=2 for preliminary design purposes.
As may be seen by review of Table 7-1, the design basis infiltration rates range from I = 0.00 to I = 0.01
inches per hour for the four areas, using a preliminary F = 2. In consideration of the natural variability of
the near-surface alluvium, NOVA recommends a design of I = 0.00 inches/hour.
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7.3 Review of Geotechnical Feasibility Criteria
7.3.1 Overview
Section C.2 of Appendix C of the BMP Manual provides seven factors should be considered by the
project geotechnical professional while assessing the feasibility of infiltration related to geotechnical
conditions. These factors are listed below
x C.2.1 Soil and Geologic Conditions
x C.2.2 Settlement and Volume Change
x C.2.3 Slope Stability
x C.2.4 Utility Considerations
x C.2.5 Groundwater Mounding
x C.2.6 Retaining Walls and Foundations
x C.2.7 Other Factors
The above geotechnical feasibility criteria are reviewed in the following subsections.
7.3.2 Soil and Geologic Conditions
The engineering borings and percolation tests borings completed for this assessment disclose the
sequence of artificial fill and rock described below.
x Unit 1, Alluvium (Qa). The site is overlain by alluvium, predominantly silty and sandy mix of
soils of medium dense to dense consistency. This unit ranges from 5 feet to 20 feet in thickness.
x Unit 2, Paralics. The alluvium material is underlain by silty and sandy soils of the Very Old
Paralic formation (Qvop). These materials are characteristically sandy dense to very dense
consistency.
The finer grained Unit 1 alluvium may be expected to be of lower permeability. This is expectation was
confirmed by the percolation testing reported in Table 7-1.
7.3.3 Settlement and Volume Change
The soils at the tested infiltration locations susceptible to settlement and/or volume change when saturated
considering the very low infiltration rate and very stiff underlying formation. Measures can be taken to
possibly mitigate this problem with the implementation of impermeable liners.
7.3.4 Slope Stability
The periphery of the site (to the south and east) includes several areas with slopes steeper than 25%.
Stormwater infiltration BMPs should not be located within 50 feet of such slopes.
Because the proposed development is still within the preliminary design stage, NOVA is not aware of any
planning to locate stormwater infiltration BMPs within 25 feet of slopes steeper than 25% (i.e., slopes
steeper than 4H: 1V).
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7.3.5 Utilities
Stormwater infiltration BMPs should not be sited within 10 feet of underground utilities. Because the
proposed development is still within the preliminary design stage, NOVA is not aware of any utility
trenches within 10 feet of the locations of perspective BMPs. Accordingly, NOVA sees no constraint to
the feasibility of stormwater BMPs by this consideration.
7.3.6 Groundwater Mounding
Stormwater infiltration can result in damaging ground water mounding during wet periods. Mounded
water could be damaging to utilities, development infrastructure (pavements, flat work, etc.) and building
foundations.
As is discussed in Sections 7.2 and 7.3, the infiltration testing reported herein indicates that vertical
infiltration rates are low, averaging I = 0.00 inches/hour across the site. Implementation of stormwater
infiltration BMPs could result in groundwater mounding near BMPs.
7.3.7 Retaining Walls and Foundations
The BMP Manual recommends that stormwater infiltration BMPs be sited a minimum 10 feet from the
retaining walls and foundations. Infiltration in close proximity to retaining walls and foundations can be
affected by increased water infiltration and result of potential increases in lateral pressures and reductions
in soil strength. Sited as such, BMPs will not be a hazard to structures.
7.3.8 Other Factors
NOVA knows of no other geotechnical factors that could affect stormwater infiltration BMPs.
7.4 Suitability of the Site for Stormwater Infiltration
It is the judgment of NOVA that the site is not suitable for stormwater infiltration BMPs.
1. Low Design Infiltration Rate. The design infiltration rate determined from the site-specific
percolation testing yielded negligible infiltration rates. The geologic conditions do not allow for
infiltration in any appreciable amount.
2. Widespread Low Permeability Soil. The site is underlain by the unit 2 soils known to be of low
permeability and higher densities. This increases the geotechnical hazards for infiltration into the
unit 1 soils.
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8.0 PAVEMENTS
8.1 General
Similar to the requirements for control of moisture beneath floor slabs and flatwork, control of surface
drainage is important to the design and construction of pavements for this site.
Moisture must be controlled in the Unit 1 alluvium. Moreover, where standing water develops either on
the pavement surface or within the base course- softening of the subgrade and other problems related to
the deterioration of the pavement can be expected. Furthermore, good drainage should minimize the risk
of the subgrade materials becoming saturated and weakened over a long period of time.
The following recommendations should be considered to limit the amount of excess moisture, which can
reach the subgrade soils:
x maintain surface gradients at a minimum 2% grade away from the pavements;
x compact utility trenches for landscaped areas to the same criteria as the pavement subgrade;
x seal all landscaped areas in or adjacent to pavements to minimize or prevent moisture migration to
subgrade soils;
x planters should not be located next to pavements (otherwise, subdrains should be used to drain the
planter to appropriate outlets);
x place compacted backfill against the exterior side of curb and gutter; and,
x concrete curbs bordering landscaped areas should have a deepened edge to provide a cutoff for
moisture flow beneath pavements (generally, the edge of the curb can be extended an additional
twelve inches below the base of the curb).
Preventative maintenance should be planned and provided for. Preventative maintenance activities are
intended to slow the rate of pavement deterioration and to preserve the pavement investment.
Preventative maintenance consists of both localized maintenance (e.g. crack sealing and patching) and
global maintenance (e.g. surface sealing). Preventative maintenance is usually the first priority when
implementing a planned pavement maintenance program and provides the highest return on investment
for pavements.
8.2 Setback from Slopes
Pavements should be set back a minimum of 10 feet from the crest of any descending slope steeper than
4:1 (H:V). Pavements should be set back a minimum of 5 feet from the crest of slopes 4:1 (H:V) or flatter.
8.3 Subgrade Preparation
8.3.1 Rough Grading
Grading for paved areas should be as described in Section 6.3, removing and replacing the Unit 1
alluvium to a depth of two feet.
The surface of the Unit 1 soils disturbed by excavation should be moisture conditioned and re-densified.
Thereafter, this unit should be proof rolled to make sure no soft areas exist. Following proof rolling, the
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excavated soils should be moisture conditioned to at least 2% above the optimum moisture content and
replaced to at least 95% relative compaction after ASTM D 1557 (the ‘modified Proctor’). Replacement
filling should be done in lifts (i) not to exceed 10-inches thickness; or, (ii) the ability of the compaction
equipment employed to densified through a complete lift, whichever is less.
8.3.2 Proof-Rolling
After the completion of compaction/densification, areas to receive pavements should be proof-rolled. A
loaded dump truck or similar should be used to aid in identifying localized soft or unsuitable material.
Any soft or unsuitable materials encountered during this proof-rolling should be removed, replaced with
an approved backfill, and compacted. The Geotechnical Engineer can provide alternative options such as
using geogrid and/or geotextile to stabilize the subgrade at the time of construction, if necessary.
8.3.3 Moisture Control
Construction should be managed such that preparation of the subgrade immediately precedes placement
of the base course. Proper drainage of the paved areas should be provided to reduce moisture infiltration
to the subgrade.
8.3.4 Surveillance
The preparation of roadway and parking area subgrades should be observed on a full-time basis by a
representative of NOVA to confirm that any unsuitable materials have been removed and that the
subgrade is suitable for support of the proposed driveways and parking areas.
8.4 Flexible Pavements
The structural design of flexible pavement depends primarily on anticipated traffic conditions, subgrade
soils, and construction materials. Table 8.1 provides preliminary flexible pavement sections using an R-
value of 12.
Table 8-1. Preliminary Pavement Sections, R = 12
Area Traffic
Index
Asphalt
Thickness
(inches)
Base
Thickness
(inches)
Passenger Car
Driveways 5.0 39
4 6.5
Heavy Duty
Driveways 6.0 3 12.5
4 10.5
1. The above sections assume properly prepared subgrade consisting of at least
12 inches of subgrade compacted to a minimum of 95% relative compaction
after ASTM D1557, with EI <50.
2. The aggregate base materials should be placed at a minimum relative
compaction of 95%.
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8.5 Rigid Pavements
8.5.1 General
Concrete pavement sections should be developed in the same manner as undertaken for pavements:
removal of the upper 2 feet of the Unit 1 soils and replacement of that material in an engineered manner
as described in Section 8.3.1.
Concrete pavement sections consisting of 6 inches of Portland cement concrete over a base course of 6
inches and a properly prepared subgrade support a wide range of traffic indices.
Where rigid pavements are used, the concrete should be obtained from an approved mix design with the
minimum properties of Table 8-2.
Table 8-2. Recommended Concrete Requirements
Property Recommended Requirement
Compressive Strength @ 28 days 3,250 psi minimum
Modulus of Rupture @ 28 days 700 minimum
Strength Requirements ASTM C94
Minimum Cement Content 5.5 sacks/cu. yd.
Cement Type Type I Portland
Concrete Aggregate ASTM C33 and CalTrans Section
703
Aggregate Size 1 inch maximum
Maximum Water Content 0.50 lb/lb of cement
Maximum Allowable Slump 4 inches
8.5.2 Jointing and Reinforcement
Longitudinal and transverse joints should be provided as needed in concrete pavements for
expansion/contraction and isolation. Sawed joints should be cut within 24-hours of concrete placement,
and should be a minimum of 25% of slab thickness plus 1/4 inch. All joints should be sealed to prevent
entry of foreign material and doweled where necessary for load transfer.
Load transfer devices, such as dowels or keys are recommended at joints in the paving to reduce possible
offsets. Where dowels cannot be used at joints accessible to wheel loads, pavement thickness should be
increased by 25 percent at the joints and tapered to regular thickness in 5 feet.
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9.0 REFERENCES
9.1 Site Specific
Preliminary Drainage Study, Bonita Glen, Bonita Glen Drive, Chula Vista, California 91910, Latitude 33
Planning & Engineering, Job 1522.00, undated.
Bonita Glen Apartments, Studio E Architects, Project 16124, October 17, 2017.
9.2 Design
American Concrete Institute, 2002, Building Code Requirements for Structural Concrete, ACI 318-02.
American Concrete Institute, 2015, Guide to Concrete Floor and Slab Construction,ACI 302.1R-15.
ASCE, Minimum Design Load for Buildings and Other Structures, ASCE 7-10.
APWA, 2015 Standard Specifications for Public Works Construction (‘Greenbook’)
California Code of Regulations, Title 24, 2016 California Building Standards Code.
California Department of Transportation (Caltrans), 2003, Corrosion Guidelines, Version 1.0, available at
http://www.dot.ca.gov/hq/esc/ttsb/corrosion/pdf/2012-11-19-Corrosion-Guidelines.pdf.
Romanoff, Melvin. Underground Corrosion, NBS Circular 579. Reprinted by NACE, Houston, 1989.
USGS, Earthquake Hazards Program, Seismic Design Maps & Tools, accessed 24 November 2017 at:
http://earthquake.usgs.gov/hazards/designmaps/
9.3 Geologic and Site Setting
CGS, California Geological Survey, 2009, Tsunami Inundation Map for Emergency Planning, National
City Quadrangle,June 1, 2009.
Jennings, C. W. and Bryant, W. A., 2010,Fault Activity Map of California, California Geological
Survey, Geologic Data Map No. 6.
Kennedy, M.P. and Tan, S.S., 2008 Geologic Map of San Diego Quadrangle, Southern California,
California Division of Mines and Geology
Norris,R.M.andWebb,R.W.,1990,GeologyofCalifornia,SecondEdition: John Wiley& Sons, Inc.
United States Federal Emergency Management Agency (FEMA), 2012, Flood Insurance Rate Map
(FIRM), Map Number No. 06073C1914G, effective date May 16, 2012.
United States Geological Survey and California Geological Survey, 2011, Quaternary Fault and Fold
database for the United States, http://earthquake.usgs.gov/regional/qfaults/.
California Department of Water Resources, Water Data Library: found at
http://www.water.ca.gov/waterdatalibrary/
California Division of Mines and Geology (CDMG), 2008, Guidelines for Evaluating and Mitigating
Seismic Hazards in California,Special Publication 117A.
.
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PLATES
NOVA
NWE
N
S
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APPENDIX A
USE OF THE GEOTECHNICAL REPORT
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APPENDIX B
SOIL EXPLORATION LOGS
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Preliminary Geotechnical Investigation and Infiltration Study December 4, 2017
Bonita Glen Apartments, Chula Vista, CA NOVA Project 2017826
APPENDIX C
RECORDS OF INFILTRATION TESTING
Appendix I:
Forms and Checklists
BMP Design Manual-Appendices
December 2015 I-5
Categorization of Infiltration Feasibility
Condition Form I-8
Part 1 - Full Infiltration Feasibility Screening Criteria
Would infiltration of the full design volume be feasible from a physical perspective without any
undesirable consequences that cannot be reasonably mitigated?
Criteria Screening Question Yes No
1
Is the estimated reliable infiltration rate below proposed facility
locations greater than 0.5 inches per hour? The response to this
Screening Question shall be based on a comprehensive evaluation of the
factors presented in Appendix C.2 and Appendix D.
Provide basis:
7KHLQILOWUDWLRQUDWHRIWKHH[LVWLQJVRLOVIRUORFDWLRQV3WKURXJK3EDVHGRQWKHRQVLWHLQILOWUDWLRQVWXG\ZDVFDOFXODWHGWR
EHOHVVWKDQLQFKHVSHUKRXU 3 3 3 DQG3 LQFKHVSHUKRXU DIWHUDSSO\LQJDPLQLPXP
IDFWRURIVDIHW\ ) RI)
2
Can infiltration greater than 0.5 inches per hour be allowed without
increasing risk of geotechnical hazards (slope stability,
groundwater mounding, utilities, or other factors) that cannot be
mitigated to an acceptable level? The response to this Screening
Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.2.
Provide basis:
1R6HH&ULWHULRQ
;
;
Appendix I:
Forms and Checklists
BMP Design Manual-Appendices
December 2015 I-6
Form I-8 Page 2 of 4
Criteria Screening Question Yes No
3
Can infiltration greater than 0.5 inches per hour be allowed
without increasing risk of groundwater contamination (shallow
water table, storm water pollutants or other factors) that cannot be
mitigated to an acceptable level? The response to this Screening
Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.3.
Provide basis:
:DWHUFRQWDPLQDWLRQZDVQRWHYDOXDWHGE\129$6HUYLFHV,QF 129$
4
Can infiltration greater than 0.5 inches per hour be allowed
without causing potential water balance issues such as change of
seasonality of ephemeral streams or increased discharge of
contaminated groundwater to surface waters? The response to this
Screening Question shall be based on a comprehensive evaluation of
the factors presented in Appendix C.3.
Provide basis:
7KHSRWHQWLDOIRUZDWHUEDODQFHZDVQRWHYDOXDWHGE\129$6HUYLFH,QF 129$
Part 1
Result*
If all answers to rows 1 - 4 are “Yes” a full infiltration design is potentially feasible.
The feasibility screening category is Full Infiltration
If any answer from row 1-4 is “No”, infiltration may be possible to some extent but
would not generally be feasible or desirable to achieve a “full infiltration” design.
Proceed to Part 2
*To be completed using gathered site information and best professional judgment considering the definition of MEP in
the MS4 Permit. Additional testing and/or studies may be required by the City Engineer to substantiate findings
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3DUW
Appendix I:
Forms and Checklists
BMP Design Manual-Appendices
December 2015 I-7
Form I-8 Page 3 of 4
Part 2 – Partial Infiltration vs. No Infiltration Feasibility Screening Criteria
Would infiltration of water in any appreciable amount be physically feasible without any negative
consequences that cannot be reasonably mitigated?
Criteria Screening Question Yes No
5
Do soil and geologic conditions allow for infiltration in any
appreciable rate or volume? The response to this Screening Question
shall be based on a comprehensive evaluation of the factors presented in
Appendix C.2 and Appendix D.
Provide basis:
7KHLQILOWUDWLRQUDWHRIWKHH[LVWLQJVRLOVIRUORFDWLRQ3WKURXJK3EDVHGRQWKHRQVLWHLQILOWUDWLRQVWXG\ZDV
FDOFXODWHGWREHOHVVWKDQLQFKHVSHUKRXU 3 3 3 DQG3 LQFKHVSHUKRXU
DIWHUDSSO\LQJDPLQLPXPIDFWRURIVDIHW\ ) RI) ,QILOWUDWLRQUDWHVRIOHVVWKDQLQFKHVSHUKRXUDQGJUHDWHU
WKDQLQFKHVSHUKRXULPSO\WKDWJHRORJLFFRQGLWLRQVDOORZIRUSDUWLDOLQILOWUDWLRQ,QILOWUDWLRQUDWHVDUHQRW
JUHDWHUWKDQ
7KHVHZLGHVSUHDGYHU\ORZWRQRSHUPHDELOLW\VRLODQGJHRORJLFFRQGLWLRQVGRQRWDOORZIRULQILOWUDWLRQLQDQ\
DSSUHFLDEOHUDWHRUYROXPH
6
Can Infiltration in any appreciable quantity be allowed without
increasing risk of geotechnical hazards (slope stability,
groundwater mounding, utilities, or other factors) that cannot be
mitigated to an acceptable level? The response to this Screening
Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.2.
Provide basis:
&$JHRORJLFLQYHVWLJDWLRQZDVSHUIRUPHGDWWKHVXEMHFWVLWH
&7KHVRLOVDWWKHWHVWHGLQILOWUDWLRQORFDWLRQVVXVFHSWLEOHWRVHWWOHPHQWDQGRUYROXPHFKDQJHZKHQVDWXUDWHG
FRQVLGHULQJWKHYHU\ORZLQILOWUDWLRQUDWHDQGYHU\VWLIIXQGHUO\LQJIRUPDWLRQ0HDVXUHVFDQEHWDNHQWRSRVVLEO\
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DQ\VORSH
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UHWDLQLQJZDOOV
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129$
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;
;
Appendix I:
Forms and Checklists
BMP Design Manual-Appendices
December 2015 I-8
Form I-8 Page 4 of 4
Criteria Screening Question Yes No
7
Can Infiltration in any appreciable quantity be allowed without
posing significant risk for groundwater related concerns (shallow
water table, storm water pollutants or other factors)? The
response to this Screening Question shall be based on a
comprehensive evaluation of the factors presented in Appendix C.3.
Provide basis:
:DWHUFRQWDPLQDWLRQZDVQRWHYDOXDWHGE\129$6HUYLFHV,QF 129$
8
Can infiltration be allowed without violating downstream water
rights? The response to this Screening Question shall be based on a
comprehensive evaluation of the factors presented in Appendix C.3.
Provide basis:
7KHSRWHQWLDOIRUZDWHUEDODQFHZDVQRWHYDOXDWHGE\129$6HUYLFH,QF 129$
Part 2
Result*
If all answers from row 5-8 are yes then partial infiltration design is potentially
feasible. The feasibility screening category is Partial Infiltration.
If any answer from row 5-8 is no, then infiltration of any volume is considered to
be infeasible within the drainage area. The feasibility screening category is No
Infiltration.
*To be completed using gathered site information and best professional judgment considering the definition of MEP in
the MS4 Permit. Additional testing and/or studies may be required by the City Engineer to substantiate findings.
1R,QILOWUDWLRQ
Preliminary Geotechnical Investigation and Infiltration Study December 4, 2017
Bonita Glen Apartments, Chula Vista, CA NOVA Project 2017826
APPENDIX D
LABORATORY ANALYTICAL RESULTS
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