HomeMy WebLinkAboutPD 2021-0002; 3304 JAMES DRIVE; FINAL SOILS REPORT; 2022-06-21FINAL REPORT OF TESTING
AND OBSERVATION SERVICES
PERFORMED DURING SITE
GRADING
3304 JAMES DRIVE
PERMIT NO. GR2021-0002
CARLSBAD, CALIFORNIA
PREPARED FOR
JUNE 21, 2022
PROJECT NO. G2633-11-02
California West
Project No. G2633-11-02
June 21, 2022
California West Communities
5927 Priestly Drive, Suite 110
Carlsbad, California 92008
Attention: Mr. Chris Larsen
Subject: FINAL REPORT OF TESTING AND OBSERVATION SERVICES
PERFORMED DURING SITE GRADING
3304 JAMES DRIVE
PERMIT NO. GR2021-0002
CARLSBAD, CALIFORNIA
Dear Mr. Larsen:
In accordance with your request, we provided testing and observation services during the grading
operations for subject property from August 23 through September 1, 2021. The scope of our services
summarized in this report include:
Observing grading and import operations including the removal of topsoil and placement of
compacted fill across the lot.
Performing in-place density and moisture content tests on fill placed and compacted during the
grading operations.
Performing laboratory tests on samples of soil at finish grade to evaluate expansion
characteristics and water-soluble sulfate.
Preparing an As-Graded Geologic Map.
Preparing this final report of grading.
GENERAL
The subject project consists of a residential flag lot located behind an existing residence fronting
James Drive in the City of Carlsbad, California (see Vicinity Map). JC Grading performed the grading
for the development.
GEOCON
INCORPORATED
G E OT E CHN I CAL ■E NV I RONMENTA L ■ MA T ER I A L S
6960 Flanders Drive ■ Son Diego, California 92121-297 4 ■ Telephone 858.558.6900 ■ Fax 858.558.6159
Geocon Project No. G2633-11-02 - 2 - June 21, 2022
Vicinity Map
To aid in preparing this report, we reviewed the following report and plans associated with the project:
1.Geotechnical Investigation, 3304 James Drive, Carlsbad, California, prepared by Geocon
Incorporated, dated January 8, 2021 (Project No. G2633-11-02).
2.Grading Plans For: 3304 James Drive SFD, Carlsbad, California, prepared by Pasco Laret
Suiter & Associates, dated July 23, 2021.
References to elevations and locations presented herein were based on the surveyor’s or grade
checker’s stakes in the field, surveyed bottom elevations, and/or interpolation from the referenced
grading plan. Geocon Incorporated does not provide surveying services and, therefore, has no opinion
regarding the accuracy of the as-graded elevations or surface geometry with respect to the approved
plans or proper surface drainage.
GRADING
This report pertains to the grading operations for the subject development. Grading consisted of the
removal of approximately 2 feet of topsoil across the lot and driveway to expose dense formational
materials and the placement of properly compacted fill within the building pad. In addition, import
soils were required to achieve final finish pad grade. The As-Graded Geologic Map depicts the general
geologic conditions observed during grading.
Geocon Project No. G2633-11-02 - 3 - June 21, 2022
As-Graded Geologic Map
During the grading operations, we observed compaction procedures and performed in-place density
tests to evaluate the dry density and moisture content of the fill materials. We performed in-place
density tests in general conformance with ASTM Test Method D 6938 (nuclear). Table I presents the
results of the in-place dry density and moisture content tests. In general, the in-place density test
results indicate the compacted fill possesses a dry density of at least 90 percent of the laboratory
maximum dry density near to slightly above optimum moisture content at the locations tested. The
As-Graded Geologic Map presents the approximate locations of the in-place density tests for the lot.
We performed laboratory tests on soil used as compacted fill to evaluate the maximum dry
density/optimum moisture content (ASTM D 1557), expansion index (ASTM D 4829), and water-
soluble sulfate content (California Test No. 417) characteristics. Tables II through IV summarize
the results of the laboratory tests.
SOIL AND GEOLOGIC CONDITIONS
The soil and geologic conditions encountered during grading are like those described in the referenced
geotechnical report. The placement of compacted fill was also performed in accordance with
recommendations provided in the referenced geotechnical report. The lot is underlain by compacted
fill (Qcf) approximately 3 to 5 feet thick overlying Old Paralic Deposits (Qop). Differential fill
thickness across building pad is generally less than two feet. In general, the compacted fill derived
from on-site removals consist of silty sand. Import soils were required to achieve finish grade and
consists of sandy silt. The As-Graded Geologic Map shows the geologic conditions of the lot.
f."-fl.LCi1>£A,oc.u ~0~Tl01oQ'IOOI ,.02'11DlDI
I
SCM.Ct"•IIY
GEOCONLEGEND
Qcf ... COMPACTED FILL
Cop ... OLD PARALIC DEPOSITS •o INDICATES WHERE BURIED
f'rnl ... ELEVATION AT REMOVAL t..:.:::J BOTTOMS {FEET. MSL)
[!] ... APPROXIMATE LOCATION OF
GRADING TESTS
•FG INDICATES FINISH GRADE
f/(Qo
·8 '
GLE FAMILY RESID
FF=161.87
PAD•1B1.2 /
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Geocon Project No. G2633-11-02 - 4 - June 21, 2022
CONCLUSIONS AND RECOMMENDATIONS
1.0 General
1.1 Based on observations and test results, we opine the soil and geologic engineering
aspects of the site grading were performed in substantial conformance with the
recommendations of the referenced geotechnical report and approved grading plans.
1.2 Soil and geologic conditions encountered during grading that differ from those expected in the
referenced geotechnical report are not uncommon. We did not observe soil or geologic conditions
during grading that would preclude the continued development of the property as planned. Based
on laboratory test results and field observations, we opine the fill observed and tested as part of
the grading for this project was generally compacted to a dry density of at least 90 percent of the
laboratory maximum dry density near to slightly above optimum moisture content.
1.3 The site is underlain by compacted fill overlying Old Paralic Deposits. We observed the
placement of compacted fill during the grading operations and performed in-place density
tests to evaluate the dry density and moisture content of the fill material.
1.4 Laboratory testing of near-grade soil conditions indicates the upper approximately 3 feet of
soil underlying the pad possess a “very low” to “high” expansion potential (expansion index
of 130 or less). In addition, the samples indicate the soil possesses “S0” water-soluble
sulfate exposure class. Tables III and IV present the results of the laboratory expansion
index and water-soluble sulfate tests.
1.5 We understand the proposed building will be supported on a post-tensioned shallow-
foundation system.
1.6 Excavations within the fill and underlying Old Paralic Deposits should generally be possible
with moderate to heavy effort using conventional heavy-duty equipment.
2.0 Finish Grade Soil Conditions
2.1 Observations and laboratory test results indicate that the prevailing soil conditions within
the upper approximately 3 feet of finish pad grade are “expansive” (expansion index [EI]
greater than 20) as defined by the 2019 California Building Code (CBC) Section 1803.5.3.
The finish grade soils encountered during grading possesses a “very low” to “high”
expansion potential (EI of 130 or less) in accordance with ASTM D 4829. Table III presents
the results of the laboratory expansion index tests. Table 2.1 presents soil classifications
based on the expansion index.
Geocon Project No. G2633-11-02 - 5 - June 21, 2022
TABLE 2.1
EXPANSIVE SOIL CLASSIFICATION BASED ON EXPANSION INDEX
Expansion Index (EI) ASTM D 4829 Expansion
Classification
2016 CBC
Expansion Classification
0 – 20 Very Low Non-Expansive
21 – 50 Low
Expansive 51 – 90 Medium
91 – 130 High
Greater Than 130 Very High
2.2 We performed laboratory tests on samples of the finish-grade materials to evaluate the
percentage of water-soluble sulfate content. Table IV presents results of the laboratory
water-soluble sulfate content tests. The test results indicate the on-site materials at the
locations tested possess “S0” sulfate exposure to concrete structures as defined by 2019
CBC Section 1904 and ACI 318-14 Chapter 19. The presence of water-soluble sulfates is
not a visually discernible characteristic; therefore, other soil samples from the site could
yield different concentrations. Additionally, over time landscaping activities (i.e., addition
of fertilizers and other soil nutrients) may affect the concentration.
2.3 Geocon Incorporated does not practice in the field of corrosion engineering. Therefore,
further evaluation by a corrosion engineer may be performed if improvements susceptible to
corrosion are planned.
2.1 Seismic Design Criteria
2.1.1 Table 2.1.1 summarizes site-specific design criteria obtained from the 2019 California
Building Code (CBC; Based on the 2018 International Building Code [IBC] and ASCE 7-
16), Chapter 16 Structural Design, Section 1613 Earthquake Loads. We used the computer
program U.S. Seismic Design Maps, provided by the Structural Engineers Association
(SEA) to calculate the seismic design parameters. The short spectral response uses a period
of 0.2 second. We evaluated the Site Class based on the discussion in Section 1613.2.2 of
the 2019 CBC and Table 20.3-1 of ASCE 7-16. The values presented herein are for the risk-
targeted maximum considered earthquake (MCER). Sites designated as Site Class D, E and F
may require additional analyses if requested by the project structural engineer and client.
Geocon Project No. G2633-11-02 - 6 - June 21, 2022
TABLE 2.1.1
2019 CBC SEISMIC DESIGN PARAMETERS
Parameter Value 2019 CBC Reference
Site Class C Section 1613.2.2
MCER Ground Motion Spectral Response Acceleration – Class B (short), SS 1.038g Figure 1613.2.1(1)
MCER Ground Motion Spectral Response Acceleration – Class B (1 sec), S1 0.377g Figure 1613.2.1(2)
Site Coefficient, FA 1.2 Table 1613.2.3(1)
Site Coefficient, FV 1.5* Table 1613.2.3(2)
Site Class Modified MCER Spectral Response Acceleration (short), SMS 1.245g Section 1613.2.3 (Eqn 16-36)
Site Class Modified MCER Spectral Response Acceleration – (1 sec), SM1 0.566g* Section 1613.2.3 (Eqn 16-37)
5% Damped Design
Spectral Response Acceleration (short), SDS 0.83g Section 1613.2.4 (Eqn 16-38)
5% Damped Design Spectral Response Acceleration (1 sec), SD1 0.377g* Section 1613.2.4 (Eqn 16-39)
* Note: Using the code-based values presented in this table, in lieu of a performing a ground motion hazard
analysis, requires the exceptions outlined in ASCE 7-16 Section 11.4.8 be followed by the project structural
engineer. Per Section 11.4.8 of ASCE/SEI 7-16, a ground motion hazard analysis should be performed for
projects for Site Class “E” sites with Ss greater than or equal to 1.0g and for Site Class “D” and “E” sites with
S1 greater than 0.2g. Section 11.4.8 also provides exceptions which indicates that the ground motion hazard
analysis may be waived provided the exceptions are followed.
2.1.2 Table 2.1.2 presents the mapped maximum considered geometric mean (MCEG) seismic
design parameters for projects located in Seismic Design Categories of D through F in
accordance with ASCE 7-16.
TABLE 2.1.2
ASCE 7-16 PEAK GROUND ACCELERATION
Parameter Value ASCE 7-16 Reference
Mapped MCEG Peak Ground Acceleration, PGA 0.546g Figure 22-7
Site Coefficient, FPGA 1.2 Table 11.8-1
Site Class Modified MCEGPeak Ground Acceleration, PGAM 0.547g Section 11.8.3 (Eqn 11.8-1)
2.1.3 Conformance to the criteria in Tables 2.1.1 and 2.1.2 for seismic design does not constitute
any kind of guarantee or assurance that significant structural damage or ground failure will
not occur in the event of a large earthquake. The primary goal of seismic design is to protect
life, not to avoid all damage, since such design may be economically prohibitive.
2.1.4 The project structural engineer and architect should evaluate the appropriate Risk Category
and Seismic Design Category for the planned structures. The values presented herein
Geocon Project No. G2633-11-02 - 7 - June 21, 2022
assume a Risk Category of II and resulting in a Seismic Design Category D. Table 2.1.3
presents a summary of the risk categories in accordance with ASCE 7-16.
TABLE 2.1.3
ASCE 7-16 RISK CATEGORIES
Risk Category Building Use Examples
I Low risk to Human Life at Failure Barn, Storage Shelter
II Nominal Risk to Human Life at Failure (Buildings Not Designated as I, III or IV) Residential, Commercial and Industrial Buildings
III Substantial Risk to
Human Life at Failure
Theaters, Lecture Halls, Dining Halls, Schools, Prisons, Small Healthcare Facilities, Infrastructure Plants, Storage for Explosives/Toxins
IV Essential Facilities
Hazardous Material Facilities, Hospitals, Fire and Rescue, Emergency Shelters, Police Stations, Power
Stations, Aviation Control Facilities, National Defense, Water Storage
2.2 Post-Tensioned Foundations
2.2.1 The post-tensioned system should be designed by a structural engineer experienced in post-
tensioned slab design and design criteria of the Post-Tensioning Institute (PTI) DC10.5 as required
by the 2019 California Building Code (CBC Section 1808.6.2). Although this procedure was
developed for expansive soil conditions, we understand it can also be used to reduce the potential
for foundation distress due to differential fill settlement. The post-tensioned design should
incorporate the geotechnical parameters presented on Table 2.2.1. The parameters presented in
Table 2.2.1 are based on the guidelines presented in the PTI, DC10.5 design manual. The lot is
classified as foundation category II for design of the building foundation system where the soils are
considered expansion with a weighted expansion classification of “medium” (expansion index of
51 to 90) based on the upper foot of finish grade soil having an expansion index of 91 to 130 and
having an expansion index of 0 to 20 from 1 foot to 4 feet below grade.
TABLE 2.2.1
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PTI)DC10.5 Design Parameters Value
Thornthwaite Index -20
Equilibrium Suction 3.9
Edge Lift Moisture Variation Distance, eM (feet) 5.1
Edge Lift, yM (inches) 1.10
Center Lift Moisture Variation Distance, eM (feet) 9.0
Center Lift, yM (inches) 0.47
Geocon Project No. G2633-11-02 - 8 - June 21, 2022
2.2.2 The foundations for the post-tensioned slabs should be embedded in accordance with the
recommendations of the structural engineer. If a post-tensioned mat foundation system is
planned, the slab should possess a thickened edge with a minimum width of 12 inches and
extend below the clean sand or crushed rock layer.
2.2.3 If the structural engineer proposes a post-tensioned foundation design method other than the
2019 CBC (PTI DC10.5):
The criteria presented in Table 2.2.1 are still applicable.
Interior stiffener beams should be used.
The width of the perimeter foundations should be at least 12 inches.
The perimeter footing embedment depths should be at least 12 inches. The
embedment depths should be measured from the lowest adjacent pad grade.
2.2.4 Isolated foundations located outside of the proposed post-tensioned slab should consist of
continuous strip footings and/or isolated spread footings. Table 2.2.2 provides a summary of
the foundation design recommendations.
TABLE 2.2.2
SUMMARY OF FOUNDATION RECOMMENDATIONS
Parameter Value
Minimum Continuous Foundation Width, WC 12 inches
Minimum Isolated Foundation Width, WI 24 inches
Minimum Foundation Depth, D 18 Inches Below Lowest Adjacent Grade
Minimum Steel Reinforcement – Continuous 4 No. 4 Bars, 2 at the Top and 2 at the Bottom
Weighted Design Expansion Index 90 or less
2.2.5 The conventional shallow foundations should be embedded in accordance with the
recommendations herein and the Wall/Column Footing Dimension Detail. The embedment
depths should be measured from the lowest adjacent pad grade for both interior and exterior
footings. Footings should be deepened such that the bottom outside edge of the footing is at
least 7 feet horizontally from the face of the slope (unless designed with a post-tensioned
foundation system as discussed herein).
Geocon Project No. G2633-11-02 - 9 - June 21, 2022
Wall/Column Footing Dimension Detail
2.2.6 Our experience indicates post-tensioned slabs are susceptible to excessive edge lift,
regardless of the underlying soil conditions. Placing reinforcing steel at the bottom of the
perimeter footings and the interior stiffener beams may mitigate this potential. Current PTI
design procedures primarily address the potential center lift of slabs but, because of the
placement of the reinforcing tendons in the top of the slab, the resulting eccentricity after
tensioning reduces the ability of the system to mitigate edge lift. The structural engineer
should design the foundation system to reduce the potential of edge lift occurring for the
proposed structures.
2.2.7 During the construction of the post-tension foundation system, the concrete should be
placed monolithically. Under no circumstances should cold joints form between the
footings/grade beams and the slab during the construction of the post-tension foundation
system unless designed by the project structural engineer.
2.2.8 The proposed structure can be supported on a shallow foundation system founded in the
compacted fill materials. Table 2.2.3 provides a summary of the foundation design
recommendations.
TABLE 2.2.3
SUMMARY OF FOUNDATION RECOMMENDATIONS
Parameter Value
Allowable Bearing Capacity 2,500 psf
Estimated Total Settlement ½ Inch
Estimated Differential Settlement ½ Inch in 40 Feet
(D 0 z --I I-1-0 o.. 0 LU u...o
SAND AND VAPOR
RETARDER IN
ACCORDANCE WITH ACI -:>?:'.;;;.
:'\'. 4-.: .• : -.-.·./_. .. :=:_-/.,:.
I.. ..I FOOTING
WIDTH, We
PAD GRADE
(DJ: ~ I-I-Q. OL.U 00 u...
Geocon Project No. G2633-11-02 - 10 - June 21, 2022
2.2.9 The bearing capacity values presented herein are for dead plus live loads and may be
increased by one-third when considering transient loads due to wind or seismic forces.
2.2.10 The use of isolated footings, which are located beyond the perimeter of the building and
support structural elements connected to the building, are not recommended. Where this
condition cannot be avoided, the isolated footings should be connected to the building
foundation system with grade beams in both directions.
2.2.11 Consideration should be given to using interior stiffening beams and connecting isolated
footings and/or increasing the slab thickness.
2.2.12 Slabs that may receive moisture-sensitive floor coverings or may be used to store moisture-
sensitive materials should be underlain by a vapor retarder. The vapor retarder design should
be consistent with the guidelines presented in the American Concrete Institute’s (ACI) Guide
for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials (ACI 302.2R-06). In
addition, the membrane should be installed in accordance with manufacturer’s
recommendations and ASTM requirements and installed in a manner that prevents puncture.
The vapor retarder used should be specified by the project architect or developer based on the
type of floor covering that will be installed and if the structure will possess a humidity-
controlled environment.
2.2.13 The bedding sand thickness should be determined by the project foundation engineer,
architect, and/or developer. It is common to have 3 to 4 inches of sand for 5-inch and 4-inch
thick slabs, respectively, in the southern California region. However, we should be
contacted to provide recommendations if the bedding sand is thicker than 6 inches. The
foundation design engineer should provide appropriate concrete mix design criteria and
curing measures to assure proper curing of the slab by reducing the potential for rapid
moisture loss and subsequent cracking and/or slab curl. We suggest that the foundation
design engineer present the concrete mix design and proper curing methods on the
foundation plans. It is critical that the foundation contractor understands and follows the
recommendations presented on the foundation plans.
2.2.14 We should observe the foundation excavations prior to the placement of reinforcing steel to
check that the exposed soil conditions are similar to those expected and that they have been
extended to the appropriate bearing strata. If unexpected soil conditions are encountered,
foundation modifications may be required.
Geocon Project No. G2633-11-02 - 11 - June 21, 2022
2.3 Driveway and Exterior Concrete Flatwork
2.3.1 The driveway and other exterior concrete flatwork should be constructed in accordance with
the recommendations presented in Table 2.3. The recommended steel reinforcement would
help reduce the potential for cracking.
TABLE 2.3
MINIMUM CONCRETE DRIVEWAY AND FLATWORK RECOMMENDATIONS
Expansion
Index, EI Minimum Steel Reinforcement* Options Minimum
Thickness
EI < 90 6x6-W2.9/W2.9 (6x6-6/6) welded wire mesh 4 Inches No. 4 Bars 18 inches on center, Both Directions
EI < 130 4x4-W4.0/W4.0 (4x4-4/4) welded wire mesh 4 Inches No. 4 Bars 12 inches on center, Both Directions
* In excess of 8 feet square.
2.3.2 The subgrade soil should be properly moisturized and compacted prior to the placement of
steel and concrete. The subgrade soil should be compacted to a dry density of at least 90
percent of the laboratory maximum dry density near to slightly above optimum moisture
content in accordance with ASTM D 1557.
2.3.3 Even with the incorporation of the recommendations of this report, concrete has a potential to
experience some uplift due to expansive soil beneath grade. The steel reinforcement should
overlap continuously in flatwork to reduce the potential for vertical offsets within flatwork.
Additionally, driveway concrete should be structurally connected to the curbs, where possible,
to reduce the potential for offsets between the curbs and the driveway.
2.3.4 Concrete should be provided with crack control joints to reduce and/or control shrinkage
cracking. Crack control spacing should be determined by the project structural engineer
based upon the slab thickness and intended usage. Criteria of the American Concrete
Institute (ACI) should be taken into consideration when establishing crack control spacing.
Subgrade soil for exterior slabs not subjected to vehicle loads should be compacted in
accordance with criteria presented in the grading section prior to concrete placement.
Subgrade soil should be properly compacted and the moisture content of subgrade soil
should be verified prior to placing concrete. Base materials will not be required below
concrete improvements.
2.3.5 Where exterior flatwork abuts the structure at entrant or exit points, the exterior slab should
be dowelled into the structure’s foundation stemwall. This recommendation is intended to
Geocon Project No. G2633-11-02 - 12 - June 21, 2022
reduce the potential for differential elevations that could result from differential settlement
or minor heave of the flatwork. Dowelling details should be designed by the project
structural engineer.
2.3.6 The recommendations presented herein are intended to reduce the potential for cracking of
exterior slabs as a result of differential movement. However, even with the incorporation of
the recommendations presented herein, slabs-on-grade will still crack. The occurrence of
concrete shrinkage cracks is independent of the soil supporting characteristics. Their
occurrence may be reduced and/or controlled by limiting the slump of the concrete, the use
of crack control joints and proper concrete placement and curing. Crack control joints
should be spaced at intervals no greater than 12 feet. Literature provided by the Portland
Concrete Association (PCA) and American Concrete Institute (ACI) present
recommendations for proper concrete mix, construction, and curing practices, and should be
incorporated into project construction.
2.4 Retaining Walls
2.4.1 Retaining walls should be designed using the values presented in Table 2.4.1. Soil with an
expansion index (EI) of greater than 50 should not be used as backfill material behind retaining
walls.
TABLE 2.4.1
RETAINING WALL DESIGN RECOMMENDATIONS
Parameter Value
Active Soil Pressure, A (Fluid Density, Level Backfill) 35 pcf
Active Soil Pressure, A (Fluid Density, 2:1 Sloping Backfill) 50 pcf
Seismic Pressure, S 10H psf
At-Rest/Restrained Walls Additional Uniform Pressure (0 to 8 Feet High) 7H psf
At-Rest/Restrained Walls Additional Uniform Pressure (8+ Feet High) 13H psf
Expected Expansion Index for the Subject Property EI<50
H equals the height of the retaining portion of the wall
2.4.2 The project retaining walls should be designed as shown in the Retaining Wall Loading
Diagram.
Geocon Project No. G2633-11-02 - 13 - June 21, 2022
Retaining Wall Loading Diagram
2.4.3 Unrestrained walls are those that are allowed to rotate more than 0.001H (where H equals
the height of the retaining portion of the wall) at the top of the wall. Where walls are
restrained from movement at the top (at-rest condition), an additional uniform pressure
should be applied to the wall. For retaining walls subject to vehicular loads within a
horizontal distance equal to two-thirds the wall height, a surcharge equivalent to 2 feet of fill
soil should be added.
2.4.4 The structural engineer should determine the Seismic Design Category for the project in
accordance with Section 1613.3.5 of the 2019 CBC or Section 11.4 of ASCE 7-16. For
structures assigned to Seismic Design Category of D, E, or F, retaining walls that support
more than 6 feet of backfill should be designed with seismic lateral pressure in accordance
with Section 1803.5.12 of the 2019 CBC. The seismic load is dependent on the retained
height where H is the height of the wall, in feet, and the calculated loads result in pounds per
square foot (psf) exerted at the base of the wall and zero at the top of the wall.
2.4.5 Retaining walls should be designed to ensure stability against overturning sliding, and
excessive foundation pressure. Where a keyway is extended below the wall base with the
intent to engage passive pressure and enhance sliding stability, it is not necessary to
consider active pressure on the keyway.
2.4.6 Drainage openings through the base of the wall (weep holes) should not be used where the
seepage could be a nuisance or otherwise adversely affect the property adjacent to the base
IF PRESENT
RETAINING
WALL
SLAB
ACTIVE
PRESSURE
H (Feet)
---FOOTING
SEISMIC
(IF
REQUIRED)
AT-REST/
RESTRAINED
(IF REQUIRED) r
H ::,8' Ru
Ri_ psf ---H>8'
Geocon Project No. G2633-11-02 - 14 - June 21, 2022
of the wall. The recommendations herein assume a properly compacted granular (EI of 50 or
less) free-draining backfill material with no hydrostatic forces or imposed surcharge load.
The retaining wall should be properly drained as shown in the Typical Retaining Wall
Drainage Detail. If conditions different than those described are expected, or if specific
drainage details are desired, Geocon Incorporated should be contacted for additional
recommendations.
Typical Retaining Wall Drainage Detail
2.4.7 The retaining walls may be designed using either the active and restrained (at-rest) loading
condition or the active and seismic loading condition as suggested by the structural
engineer. Typically, it appears the design of the restrained condition for retaining wall
loading may be adequate for the seismic design of the retaining walls. However, the active
earth pressure combined with the seismic design load should be reviewed and also
considered in the design of the retaining walls.
2.4.8 In general, wall foundations should be designed in accordance with Table 2.4.2. The
proximity of the foundation to the top of a slope steeper than 3:1 could impact the allowable
soil bearing pressure. Therefore, retaining wall foundations should be deepened such that the
bottom outside edge of the footing is at least 7 feet horizontally from the face of the slope.
TABLE 2.4.2
SUMMARY OF RETAINING WALL FOUNDATION RECOMMENDATIONS
Parameter Value
Minimum Retaining Wall Foundation Width 12 inches
Minimum Retaining Wall Foundation Depth 12 Inches
Minimum Steel Reinforcement Per Structural Engineer
Allowable Bearing Capacity 2,500 psf
Estimated Total Settlement ½ Inch
Estimated Differential Settlement ½ Inch in 40 Feet
H
PROPOSED
GRADE
CONCRETE BROWDITCH
TEMPORARY
BACKCUTPER
OSHA
OR
Fl 140N FILTER
RIC (OR EQUIVALENT)
RETAINING
WALL
213 H
PROPOSED
GRADE
4" DIA. PERFORATED SCHEDULE 40
PVC PIPE EXTENDED TO APPROVED
OUTLET
GROUND SURFACE
DRAINAGE PANEL (MIRADRAIN
6000 OR EQUIVALENT)
314" CRUSHED ROCK (1 CU. FT./FT.)
OR WRAP DRAINAGE PANEL
12" AROUND PIPE
.:r.,-"7; LTER FABRIC ENVELOPE
''!';\;.yMIRAFI 140N OR EQUIVALENT
4" DIA SCHEDULE 40 PERFORATED
PVC PIPE OR TOTAL DRAIN EXTENDED
TO APPROVED OUTLET
Geocon Project No. G2633-11-02 - 15 - June 21, 2022
2.4.9 The recommendations presented herein are generally applicable to the design of rigid
concrete or masonry retaining walls. In the event that other types of walls (such as
mechanically stabilized earth [MSE] walls, soil nail walls, or soldier pile walls) are planned,
Geocon Incorporated should be consulted for additional recommendations.
2.4.10 Unrestrained walls will move laterally when backfilled and loading is applied. The amount
of lateral deflection is dependent on the wall height, the type of soil used for backfilling, and
loads acting on the wall. The retaining walls and improvements above the retaining walls
should be designed to incorporate an appropriate amount of lateral deflection as determined
by the structural engineer.
2.4.11 Soil contemplated for use as retaining wall backfill, including import materials, should be
identified in the field prior to backfill. At that time, Geocon Incorporated should obtain
samples for laboratory testing to evaluate its suitability. Modified lateral earth pressures
may be necessary if the backfill soil does not meet the required expansion index or shear
strength. City or regional standard wall designs, if used, are based on a specific active lateral
earth pressure and/or soil friction angle. In this regard, on-site soil to be used as backfill may
or may not meet the values for standard wall designs. Geocon Incorporated should be
consulted to assess the suitability of the on-site soil for use as wall backfill if standard wall
designs will be used.
2.5 Lateral Loading
2.5.1 Table 2.5 should be used to help design the proposed structures and improvements to
resist a horizontal surface extending at least 5 feet, or three times the surface generating
the passive pressure, whichever is greater. The upper 12 inches of material in areas not
lateral loads for the design of footings or shear keys. The allowable passive pressure
assumes protected by floor slabs or pavement should not be included in design for passive
resistance.
TABLE 2.5
SUMMARY OF LATERAL LOAD DESIGN RECOMMENDATIONS
Parameter Value
Passive Pressure Fluid Density 350 pcf
Coefficient of Friction (Concrete and Soil) 0.35
Coefficient of Friction (Along Vapor Barrier) 0.2 to 0.25*
* Per manufacturer’s recommendations.
Geocon Project No. G2633-11-02 - 16 - June 21, 2022
2.5.2 The passive and frictional resistant loads can be combined for design purposes. The lateral
passive pressures may be increased by one-third when considering transient loads due to
wind or seismic forces.
3.0 Site Drainage and Moisture Protection
3.1 Adequate site drainage is critical to reduce the potential for differential soil movement,
erosion, and subsurface seepage. Under no circumstances should water be allowed to pond
adjacent to footings. The site should be graded and maintained such that surface drainage is
directed away from structures in accordance with 2019 CBC 1804.4 or other applicable
standards. In addition, surface drainage should be directed away from the top of slopes into
swales or other controlled drainage devices. Roof and pavement drainage should be directed
into conduits that carry runoff away from the proposed structure.
3.2 In the case of basement walls or building walls retaining landscaping areas, a water-proofing
system should be used on the wall and joints, and a Miradrain drainage panel (or similar)
should be placed over the waterproofing. The project architect or civil engineer should
provide detailed specifications on the plans for all waterproofing and drainage.
3.3 Underground utilities should be leak free. Utility and irrigation lines should be checked
periodically for leaks, and detected leaks should be repaired promptly. Detrimental soil
movement could occur if water is allowed to infiltrate the soil for prolonged periods of time.
3.4 Landscaping planters adjacent to paved areas are not recommended due to the potential for
surface or irrigation water to infiltrate the pavement's subgrade and base course. Area drains
to collect excess irrigation water and transmit it to drainage structures or impervious above-
grade planter boxes can be used. In addition, where landscaping is planned adjacent to the
pavement, construction of a cutoff wall along the edge of the pavement that extends at least
6 inches below the bottom of the base material should be considered.
LIMITATIONS AND UNIFORMITY OF CONDITIONS
The conclusions and recommendations contained herein apply only to our work with respect to
development and represent conditions on the date of our final observation. Any subsequent
improvement should be done in conjunction with our observation and testing services. As used herein,
the term “observation” implies only that we observed the progress of the work with which we agreed
to be involved. Our services did not include the evaluation or identification of the potential presence of
hazardous materials. Our conclusions and opinions as to whether the work essentially complies with
the job specifications are based on our observations, experience, and test results. Subsurface
conditions, and the accuracy of tests used to measure such conditions, can vary greatly at any time. We
Geocon Project No. G2633-11-02 - 17 - June 21, 2022
Project Name:Project No.:Pre. No. Re.1 08/24/21East Lot Ox158 1 0 133.5 7.4 124.8 6.9 9390208/25/21East Lot Ox159 1 0 133.5 7.4 123.9 7.4 93903 08/26/21Central Lot OX158 1 0 133.5 7.4 122.7 9.1 92904 08/26/21Central Lot OX159 1 0 133.5 7.4 123.0 8.7 92905 08/26/21West Lot OX158 1 0 133.5 7.4 122.4 9.3 92906 08/27/21West Lot OX159 1 0 133.5 7.4 122.2 8.1 9290FG 7 09/01/21Final Grade East Lot161 2 0 121.4 13.1 111.7 14.3 9290FG 8 09/01/21Final Grade West Lot161 2 0 121.4 13.1 112.0 14.8 9290TABLE ISUMMARY OF FIELD DENSITY TEST RESULTS3304 James DriveG2633-11-02Max. Dry Density (pcf)Opt. Moist Content (%)Field Dry Density (pcf)Field Moisture Content (%)Relative Compaction (%)Required Relative Compaction (%)Test No. Date (MM/DD/YY)Curve No.>¾" Rock (%)LocationElev. or Depth (feet)0GEOCON
Project Name:3304 James DriveProject No.: G2633-11-02AC Asphalt Concrete ITIrrigation TrenchSG SubgradeAD Area Drain JTJoint TrenchSL Sewer LateralBBaseMMoisture TestSM Sewer MainCG Curb/Gutter MGMinor GradingSR Slope RepairDW Driveway MSE Mechanically Stabilized Earth Wall ST Slope TestET Electrical Trench PTPlumbing TrenchSW SidewalkETB Exploratory Trench RGRegradeSZ Slope ZoneFB Footing Backfill RWL Reclaimed Water Lateral UT Utility TrenchFG Finish Grade RWM Reclaimed Water Main WB Wall BackfillFS Fire Service SBTSubdrain TrenchWL Water LateralGT Gas Trench SDStorm DrainWM Water MainA, B, C, …R*SC Denotes Sandcone Density TestFill in area of density test was removed during construction operationsELEVATION OR DEPTHTABLE ISUMMARY OF FIELD DENSITY TEST RESULTSTEST NO. - PREFIXTEST NO. - RE.Retest of previous density test failure following additional moisture conditioning or recompactionCorresponds to the elevation or the depth, in feet, of the in-place density/moisture content test. The value has been rounded to the nearest whole foot. CURVE NO.Corresponds to the curve numbers presented in the summary of the laboratory maximum dry density and optimum moisture content test results. The field representative selected the curve no. based on the laboratory test results and field observations.>¾" ROCK - ROCK CORRECTIONThe laboratory maximum dry density and optimum moisture content can be adjusted for in-place soil that possesses rock larger than ¾ inch. The curve no. is adjusted for the percentage of ¾ inch rock in accordance with ASTM D 4718 or Woodward Clyde guidelines.0GEOCON
Geocon Project No. G2633-11-02 June 21, 2022
TABLE II
SUMMARY OF LABORATORY MAXIMUM DRY DENSITY
AND OPTIMUM MOISTURE CONTENT TEST RESULTS
ASTM D 1557
Sample
No. Description
Maximum
Dry Density
(pcf)
Optimum
Moisture Content
(% dry weight)
1 Dark brown, Silty, fine to medium SAND 133.5 7.4
2 Brown, Sandy SILT (Import) 121.4 13.1
TABLE III
SUMMARY OF LABORATORY EXPANSION INDEX TEST RESULTS
ASTM D 4829
Sample No.
Moisture Content (%) Dry Density
(pcf)
Expansion
Index
2019 CBC Soil
Expansion
Classification
ASTM Soil
Expansion
Classification Before Test After Test
EI-1 7.6 14.0 119.5 0 Non-Expansive Very Low
EI-2 15.0 35.0 94.0 107 Expansive High
EI-3 13.0 30.8 99.9 95 Expansive High
TABLE IV
SUMMARY OF WATER-SOLUBLE SULFATE LABORATORY TEST RESULTS
CALIFORNIA TEST NO. 417
Sample No. Water-Soluble Sulfate (%) ACI 318 Sulfate Exposure
EI-1 0.004 S0
EI-2 0.085 S0