HomeMy WebLinkAboutCT 05-18; SEASCAPE; FINAL SOILS REPORT; 2017-04-28FINAL REPORT OF TESTING AND OBSERVATION SERVICES PERFORMED DURING GRADING OPERATIONS
SEASCAPE PROPERTY
PROJECT NO. CT 05-18/GR 2016-0004
CARLSBAD, CALIFORNIA
PREPARED FOR SEASCAPE DEVELOPMENT LLC SAN DIEGO, CALIFORNIA
APRIL 28, 2017
PROJECT NO. G2054-11-01
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Project No. G2054-11-01
April 28, 2017 Seascape Development LLC 6540 Lusk Boulevard, Suite C135 San Diego, California 92121 Attention: Mr. Roger Bhatia Subject: FINAL REPORT OF TESTING AND OBSERVATION SERVICES PERFORMED DURING GRADING OPERATIONS SEASCAPE PROPERTY PROJECT NO. CT 05-18/GR 2016-0004 CARLSBAD, CALIFORNIA
Dear Mr. Bhatia: We prepared this final report of grading to summarize our testing and observation services for the
project and to provide foundation recommendations for the Seascape property to develop 12, single-
family residences in the City of Carlsbad, California. The grading has been completed and is the
subject of this report. We performed our services during the period of March 6 through April 24, 2017.
The scope of our services included:
• Observing the grading operations including the removal of surficial soil and the upper weathered portion of the Terrace Deposits within the limits of grading.
• Performing in-place density and moisture content tests in fill placed and compacted at the site during grading operations.
• Performing laboratory tests to aid in evaluating the maximum dry density and optimum moisture content of the compacted fill. Additionally, we performed laboratory tests on samples of soil present at finish grade to evaluate expansion characteristics and water-soluble sulfate content.
• Preparing an As-Graded Geologic Map.
• Preparing this final report of grading.
The purpose of this report is to document that the grading for the Seascape Property has been
completed in conformance with the recommendations of the project geotechnical report and that the
fill materials have been properly placed and compacted in accordance with the project geotechnical
report and the City of Carlsbad Grading Ordinance.
GEOCON
INCORPORATED
GEOTECHNICAL ■ ENVIRONMENTAL ■
6960 Flanders Drive ■ San Diego, California 92121-297 4 ■ Telephone 858.558.6900 ■ Fax 858.558.6159
Project No. G2054-11-01 - 2 - April 28, 2017
GENERAL
The Seascape Property is located east of Black Rail Road, north of Avena Court East and south of
Ocean Crest Avenue (see Vicinity Map, Figure 1). The site will be accessed from three entry roadways
from the southern extension of Surf Crest Street on the north, connecting to Avena Court East to the
south and by constructing Peregrine Place that will connect to Avena Court East on the west portion of
the site. The planned development area was graded to the design finish grade elevations to include 12
single-family residences and roadways with accommodating utilities and landscaping. Pratt Equipment
Corporation of Encinitas, California performed the grading operations.
Grading plans for the project are titled Grading Plan for: Seascape, prepared by Civcom &
Associates, city approval date of February 19, 2017. The project soils report is entitled Preliminary
Geotechnical Investigation, Proposed Residential Subdivision, Northeast of Avena Court and Black
Rail Road, Carlsbad, California, prepared by Leighton and Associates, Inc. dated September 29, 2004.
References to elevations and locations presented herein were based on the surveyor’s or grade
checker’s stakes in the field, 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
Grading consisted of removal of undocumented fill, topsoil and slopewash deposits and the upper
weathered portion of the Terrace Deposits to expose dense to very dense Pleistocene-age Terrace
Deposits and the placement and compaction of fill materials to achieve finish grade elevations. Prior to
placing fill, the exposed ground surface was processed, moisture conditioned as necessary, and
compacted. Fill materials derived from on-site excavations were then placed and compacted in layers in
accordance with the project requirements until design finish grade elevations were obtained.
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 summarizes
the results of the in-place dry density and moisture content tests. In general, the in-place density test
results indicate the 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 approximate
locations of the in-place density tests are plotted on the As-Graded Geologic Map (Figure 2, Map
Pocket). We tested laboratory samples used for fill to evaluate moisture-density relationships,
optimum moisture content and maximum dry density (ASTM D 1557). In addition, we obtained soil
samples at finish grade to evaluate expansion potential (ASTM D 4829), water-soluble sulfate content
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(California Test No. 417). Tables II through IV at the end of this report present the results of the
laboratory tests.
Slopes
Cut and fill slopes were constructed during grading with a maximum height of approximately 20 feet at
inclinations of 2:1 (horizontal to vertical) or flatter. Slopes should be planted, drained, and maintained to
reduce erosion. Slope irrigation should be kept to a minimum to just support the vegetative cover.
Surface drainage should not be allowed to flow over the top of the slope.
Finish Grade Soil Conditions
The soil encountered during grading operations is considered to be “non-expansive” (Expansion Index
[EI] of 20 or less) as defined by 2013/2016 California Building Code (CBC) Section 1803.5.3. Table 1
presents soil classifications based on the expansion index. The finish grade soils encountered during
grading possesses a “very low” expansion potential (EI of 20 or less). Table III at the end of this report
presents the results of the laboratory expansion index tests.
TABLE 1 EXPANSIVE SOIL CLASSIFICATION BASED ON EXPANSION INDEX
Expansion Index (EI) Expansive Soil Classification 2013/2016 CBC Expansion Classification
0 – 20 Very Low Non-Expansive
21 – 50 Low
Expansive 51 – 90 Medium
91 – 130 High
Greater Than 130 Very High
We also performed water-soluble sulfate testing on samples obtained for expansion index testing to
evaluate the amount of water-soluble sulfates within the finish-grade soil. These test results are used to
evaluate the potential for sulfate attack on normal Portland cement concrete. The test results indicate
that the on-site materials at the locations tested possess “S0” sulfate exposure class to concrete
structures as defined by 2013/2016 CBC Section 1904 and ACI 318-14 Chapter 19. Table IV presents
the results of the water-soluble sulfate tests. The presence of water-soluble sulfates is not a visually
discernible characteristic; therefore, other soil samples from the site could yield different
concentrations.
Additionally, landscaping activities (i.e., addition of fertilizers and other soil nutrients) over time may
affect the concentration. Geocon Incorporated does not practice corrosion engineering. Therefore,
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further evaluation by a corrosion engineer may be performed if improvements susceptible to corrosion
are planned.
SOIL AND GEOLOGIC CONDITIONS
The soil and geologic conditions encountered during grading were found to be similar to those
described in the project geotechnical report. Compacted fill (designated as Qcf and Quc on Figure 2)
with a thickness varying from 5 to 27 feet was placed on dense to very dense Terrace Deposits (Qt) on
Lots 5, 6, 10, 11, and 12 and Surf Crest Street. Terrace Deposits are exposed at finish grade on Lots 1
through 4 and 7 through 9, Peregrine Place and on cut slopes. The surficial soil and the weathered
portion of the Terrace Deposits were removed and replaced with compacted fill within the limits of the
planned grading. Fill materials generally consist of silty sand. The enclosed As-Graded Geologic Map
(Figure 2) depicts the general geologic conditions, bottom elevations of the fill, and in-place density
test location performed during grading operations.
We did not observe groundwater or seepage conditions during grading operations. We do not expect
groundwater to adversely impact the proposed project improvements. However, it is not uncommon
for groundwater or seepage conditions to develop where none previously existed. Groundwater
elevations are dependent on seasonal precipitation, irrigation, land use, among other factors, and vary
as a result. Proper surface drainage will be important to future performance of the project.
CONCLUSIONS AND RECOMMENDATIONS
1.0 General
1.1 Based on observations and test results, it is our opinion that the soil engineering and the
geologic engineering aspects of the grading to which this report pertains has been performed
in conformance with the recommendations of the referenced project geotechnical report, the
project grading plans and the City of Carlsbad grading ordinance. Soil and geologic
conditions encountered during grading that differ from those expected by the project soil
report are not uncommon. Where such conditions required a significant modification to the
recommendations of the project report, they have been described herein.
1.2 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, it is the opinion of Geocon Incorporated that the fill soil observed and tested
as part of the grading was compacted to a dry density of at least 90 percent of the laboratory
maximum dry density near to slightly above optimum moisture content.
Project No. G2054-11-01 - 5 - April 28, 2017
2.0 Seismic Design Criteria
2.1 We used the computer program Seismic Hazard Curves and Uniform Hazard Response
Spectra, provided by the USGS. Table 2.1 summarizes site-specific design criteria obtained
from the 2013/2016 California Building Code (CBC; Based on the 2012 and 2015
International Building Codes [IBC], respectively, and ASCE 7-10), Chapter 16 Structural
Design, Section 1613 Earthquake Loads. The short spectral response uses a period of
0.2 second. The building structures and improvements can be designed using Site Class C
and D where fill is less than 20 feet and 20 feet or greater, respectively. Table VI presents
the recommended Site Class for the subject lots/buildings. We evaluated the Site Class
based on the discussion in Section 1613.3.2 of the 2013 CBC and Table 20.3-1 of ASCE 7-
10. The values presented in Table 2.1 are for the risk-targeted maximum considered
earthquake (MCER). The 2013 CBC and the 2016 CBC seismic design parameters are equal
and can be used for the planned structures.
TABLE 2.1 2013 AND 2016 CBC SEISMIC DESIGN PARAMETERS
Parameter Value 2013 and 2016 CBC Reference
Site Class C D Section 1613.3.2
Fill Thickness, T (feet) T<20 T>20 --
MCER Ground Motion Spectral Response Acceleration – Class B (short), SS 1.093g 1.093g Figure 1613.3.1(1)
MCER Ground Motion Spectral Response
Acceleration – Class B (1 sec), S1 0.421g 0.421g Figure 1613.3.1(2)
Site Coefficient, FA 1.000 1.063 Table 1613.3.3(1)
Site Coefficient, FV 1.379 1.579 Table 1613.3.3(2)
Site Class Modified MCER Spectral Response Acceleration (short), SMS 1.093g 1.161g Section 1613.3.3 (Eqn 16-37)
Site Class Modified MCER
Spectral Response Acceleration (1 sec), SM1 0.581g 0.665g Section 1613.3.3 (Eqn 16-38)
5% Damped Design Spectral Response Acceleration (short), SDS 0.728g 0.774g Section 1613.3.4 (Eqn 16-39)
5% Damped Design Spectral Response Acceleration (1 sec), SD1 0.387g 0.443g Section 1613.3.4 (Eqn 16-40)
2.2 Table 2.2 presents additional seismic design parameters for projects located in Seismic
Design Categories of D through F in accordance with ASCE 7-10 for the mapped maximum
considered geometric mean (MCEG).
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TABLE 2.2 2013 AND 2016 CBC SITE ACCELERATION DESIGN PARAMETERS
Parameter Value ASCE 7-10 Reference or CBC Reference
Site Class C D Section 1613.3.2 (CBC)
Mapped MCEG
Peak Ground Acceleration, PGA 0.430g 0.430g Figure 22-7 (ASCE)
Site Coefficient, FPGA 1.000 1.070 Table 11.8-1 (ASCE)
Site Class Modified MCEG
Peak Ground Acceleration, PGAM 0.430g 0.460g Section 11.8.3
(Eqn 11.8-1, ASCE)
2.3 Conformance to the criteria in Tables 2.1 and 2.2 for seismic design does not constitute any
kind of guarantee or assurance that significant structural damage or ground failure will not
occur if a large earthquake occurs. The primary goal of seismic design is to protect life, not
to avoid all damage, since such design may be economically prohibitive.
3.0 Foundation and Concrete Slabs-On-Grade Recommendations
3.1 The foundation recommendations herein are for the proposed residential structures. The
foundation recommendations have been separated into three categories based on the
maximum and differential fill thickness or expansion index. Table 3.1 presents the
foundation category criteria.
TABLE 3.1 FOUNDATION CATEGORY CRITERIA
Foundation Category Maximum Fill Thickness, T (Feet) Differential Fill Thickness, D (Feet) Expansion Index (EI)
I T<20 -- EI<50
II 20<T<50 10<D<20 50<EI<90
III T>50 D>20 90<EI<130
3.2 Table 3.2 presents minimum foundation and interior concrete slab design criteria for
conventional foundation systems. Table V provides a summary of the as-graded building
pad conditions subsequent to the grading operations including expansion index and
recommended foundation category for each of the subject lots.
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TABLE 3.2 CONVENTIONAL FOUNDATION RECOMMENDATIONS BY CATEGORY
Foundation Category
Minimum Footing Embedment Depth (inches)
Continuous Footing Reinforcement Interior Slab Reinforcement
I 12 Two No. 4 bars, one top and one bottom 6 x 6 - 10/10 welded wire mesh at slab mid-point
II 18 Four No. 4 bars,
two top and two bottom
No. 3 bars at 24 inches
on center, both directions
III 24 Four No. 5 bars, two top and two bottom No. 3 bars at 18 inches on center, both directions
3.3 The concrete slab-on-grade should be a minimum of 4 inches thick for Foundation
Categories I and II and 5 inches thick for Foundation Category III.
3.4 Building foundations may be designed for an allowable soil bearing pressure of 2,000
pounds per square foot (psf) for dead plus live loads. This bearing pressure may be
increased by one-third for transient loads due to wind or seismic forces.
3.5 The embedment depths presented in Table 3.2 should be measured from the lowest adjacent
pad grade for both interior and exterior footings. The conventional foundations should have
a minimum width of 12 inches and 24 inches for continuous and isolated footings,
respectively. Figure 3 presents a wall/column footing dimension detail.
3.6 Foundation excavations should be observed by the geotechnical engineer (a representative
of Geocon Incorporated) 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.
3.7 Slabs that may receive moisture-sensitive floor coverings or may be used to store moisture-
sensitive materials should be underlain by a vapor retarder. The vapor retarder design should
be consistent with the guidelines presented in the American Concrete Institute’s (ACI) Guide
for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials (ACI 302.2R-06). 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.
Project No. G2054-11-01 - 8 - April 28, 2017
3.8 The bedding sand thickness should be determined by the project foundation engineer,
architect, and/or developer. 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.
3.9 Special subgrade presaturation is not deemed necessary prior to placing concrete; however, the
exposed foundation and slab subgrade soil should be moisture conditioned, as necessary, to
maintain a moist condition as would be expected in any such concrete placement.
3.10 Where buildings or other improvements are planned near the top of a slope steeper than 3:1
(horizontal to vertical), special foundations and/or design considerations are recommended
due to the tendency for lateral soil movement to occur.
• Building footings should be deepened such that the bottom outside edge of the footing is at least 7 feet horizontally from the face of the slope.
• Geocon Incorporated should be contacted to review pool plans and the specific site conditions to provide additional recommendations, if necessary.
• Swimming pools located within 7 feet of the top of cut or fill slopes are not recommended. Where such a condition cannot be avoided, the portion of the swimming pool wall within 7 feet of the slope face be designed assuming that the adjacent soil provides no lateral support.
• Although other improvements, which are relatively rigid or brittle, such as concrete flatwork or masonry walls, may experience some distress if located near the top of a slope, it is generally not economical to mitigate this potential. It may be possible, however, to incorporate design measures that would permit some lateral soil movement without causing extensive distress. Geocon Incorporated should be consulted for specific recommendations.
3.11 As an alternative to the conventional foundation recommendations, consideration should be
given to the use of post-tensioned concrete slab and foundation systems for the support of
the proposed structures. The post-tensioned systems should be designed by a structural
engineer experienced in post-tensioned slab design and design criteria of the Post-
Tensioning Institute (PTI), DC 10.5-12 Standard Requirements for Design and Analysis of
Shallow Post-Tensioned Concrete Foundations on Expansive Soils or WRI/CRSI Design of
Slab-on-Ground Foundations, as required by the 2013/2016 California Building Code (CBC
Section 1808.6.2). Although this procedure was developed for expansive soil conditions, it
Project No. G2054-11-01 - 9 - April 28, 2017
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 3.3 for the particular Foundation Category designated. The parameters
presented in Table 3.3 are based on the guidelines presented in the PTI, DC 10.5 design
manual. Table V provides a summary of the as-graded building pad conditions subsequent
to the grading operations including expansion index and recommended foundation category
for each of the subject lots.
TABLE 3.3 POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PTI) Third Edition Design Parameters
Foundation Category
I II III
Thornthwaite Index -20 -20 -20
Equilibrium Suction 3.9 3.9 3.9
Edge Lift Moisture Variation Distance, eM (feet) 5.3 5.1 4.9
Edge Lift, yM (inches) 0.61 1.10 1.58
Center Lift Moisture Variation Distance, eM (feet) 9.0 9.0 9.0
Center Lift, yM (inches) 0.30 0.47 0.66
3.12 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.
3.13 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. 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.
3.14 During the construction of the post-tensioned foundation system, the concrete should be
placed monolithically. Under no circumstances should cold joints form between the
footings/grade beams and the slab during the construction of the post-tension foundation
system unless designed by the structural engineer.
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3.15 Isolated footings, if present, should have the minimum embedment depth and width
recommended for conventional foundations for a particular foundation category. The use of
isolated footings, which are located beyond the perimeter of the building and support
structural elements connected to the building, are not recommended for Category III. Where
this condition cannot be avoided, the isolated footings should be connected to the building
foundation system with grade beams.
3.16 For Foundation Category III, consideration should be given to using interior stiffening
beams and connecting isolated footings and/or increasing the slab thickness. In addition,
consideration should be given to connecting patio slabs, which exceed 5 feet in width, to the
building foundation to reduce the potential for future separation to occur.
3.17 The recommendations of this report are intended to reduce the potential for cracking of slabs
due to expansive soil (if present), differential settlement of existing soil or soil with varying
thicknesses. However, even with the incorporation of the recommendations presented
herein, foundations, stucco walls, and slabs-on-grade placed on such conditions may still
exhibit some cracking due to soil movement and/or shrinkage. The occurrence of concrete
shrinkage cracks is independent of the supporting soil characteristics. Their occurrence may
be reduced and/or controlled by limiting the slump of the concrete, proper concrete
placement and curing, and by the placement of crack control joints at periodic intervals, in
particular, where re-entrant slab corners occur.
3.18 Geocon Incorporated should be consulted to provide additional design parameters as
required by the structural engineer.
4.0 Concrete Flatwork
4.1 Where exterior flatwork abuts the structure at entrant or exit areas, the exterior slab should
be dowelled into the structure’s foundation stemwall. This recommendation is intended to
reduce the potential for differential elevations that could result from differential settlement
or minor heave of the flatwork. Dowelling details should be designed by the project
structural engineer.
4.2 Exterior concrete flatwork not subject to equipment loading or vehicular or forklift traffic
should be constructed in accordance with the recommendations herein. Slab panels should
be a minimum of 4 inches thick and, when in excess of 8 feet square, should be reinforced
with 6 x 6 - W2.9/W2.9 (6 x 6 - 6/6) welded wire mesh or at least No. 3 reinforcing bars
spaced 18 inches center to center in both directions in the middle of the slab to reduce the
potential for cracking. In addition, concrete flatwork should be provided with crack control
joints to reduce and/or control shrinkage cracking. Crack control spacing should be
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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 checked prior to placing concrete.
4.3 Even with the incorporation of the recommendations within this report, the exterior concrete
flatwork has a likelihood of experiencing some movement due to swelling or settlement;
therefore, the steel reinforcement should overlap continuously in flatwork to reduce the
potential for vertical offsets within flatwork. Additionally, flatwork should be structurally
connected to the curbs, where possible, to reduce the potential for offsets between the curbs
and the flatwork.
4.4 Where exterior flatwork abuts the structure at entrant or exit points, the exterior slab should
be dowelled into the structure’s foundation stem wall. This recommendation is intended to
reduce the potential for differential elevations that could result from differential settlement
or minor heave of the flatwork. Dowelling details should be designed by the project
structural engineer.
5.0 Conventional Retaining Walls
5.1 Retaining walls not restrained at the top and having a level backfill surface should be
designed for an active soil pressure equivalent to the pressure exerted by a fluid density of
35 pounds per cubic foot (pcf). Where the backfill will be inclined at no steeper than
2:1 (horizontal to vertical), an active soil pressure of 50 pcf is recommended. These soil
pressures assume that the backfill materials within an area bounded by the wall and a 1:1
plane extending upward from the base of the wall possess an EI of 50 or less.
5.2 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, an additional uniform pressure of 7H psf should be
added to the active soil pressure where the wall possesses a height of 8 feet or less. 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.
5.3 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. The recommendations herein assume a properly compacted granular
(EI of 50 or less) free-draining backfill material with no hydrostatic forces or imposed
Project No. G2054-11-01 - 12 - April 28, 2017
surcharge load. Figure 4 presents a typical retaining wall drain detail. If conditions different
than those described are expected, or if specific drainage details are desired, Geocon
Incorporated should be contacted for additional recommendations.
5.4 The structural engineer should determine the seismic design category for the project in
accordance with Section 1613 of the CBC. If the project possesses a 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 18.3.5.12 of the 2013 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. A seismic load of 18H should be used for design. We used the peak
ground acceleration adjusted for Site Class effects, PGAM, of 0.460g calculated from ASCE 7-
10 Section 11.8.3 and applied a pseudo-static coefficient of 0.3.
5.5 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
5.6 In general, wall foundations having a minimum depth and width of 1 foot may be designed
for an allowable soil bearing pressure of 2,000 psf. The proximity of the foundation to the
top of a slope steeper than 3:1 could impact the allowable soil bearing pressure. 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.
5.7 The recommendations presented herein are generally applicable to the design of rigid concrete or
masonry retaining walls having a maximum height of 8 feet. In the event that walls higher than 8
feet or other types of walls (such as mechanically stabilized earth [MSE] walls) are planned,
Geocon Incorporated should be consulted for additional recommendations.
5.8 Unrestrained walls will move laterally when backfilled and loading is applied. The amount
of lateral deflection is dependent on the wall height, the type of soil used for backfill, and
loads acting on the wall. The retaining walls and improvements above the retaining walls
should be designed to incorporate an appropriate amount of lateral deflection as determined
by the structural engineer.
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5.9 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, the on-site soil can be used as
backfill and does meet the values for standard wall designs
6.0 Lateral Loading
6.1 To resist lateral loads, a passive pressure exerted by an equivalent fluid weight of
350 pounds per cubic foot (pcf) should be used for the design of footings or shear keys
poured neat in compacted fill. The passive pressure assumes a horizontal surface extending
at least 5 feet, or three times the surface generating the passive pressure, whichever is
greater. The upper 12 inches of material in areas not protected by floor slabs or pavement
should not be included in design for passive resistance.
6.2 If friction is to be used to resist lateral loads, an allowable coefficient of friction between
soil and concrete of 0.4 should be used for design.
6.3 The passive and frictional resistant loads can be combined for design purposes. The lateral
passive pressures may be increased by one-third when considering transient loads due to
wind or seismic forces.
7.0 Slope Maintenance
7.1 Slopes that are steeper than 3:1 (horizontal to vertical) may, under conditions which are both
difficult to prevent and predict, be susceptible to near surface (surficial) slope instability.
The instability is typically limited to the outer three feet of a portion of the slope and usually
does not directly impact the improvements on the pad areas above or below the slope. The
occurrence of surficial instability is more prevalent on fill slopes and is generally preceded
by a period of heavy rainfall, excessive irrigation, or the migration of subsurface seepage.
The disturbance and/or loosening of the surficial soils, as might result from root growth, soil
expansion, or excavation for irrigation lines and slope planting, may also be a significant
contributing factor to surficial instability. It is, therefore, recommended that, to the
maximum extent practical: (a) disturbed/loosened surficial soils be either removed or
properly recompacted, (b) irrigation systems be periodically inspected and maintained to
eliminate leaks and excessive irrigation, and (c) surface drains on and adjacent to slopes be
periodically maintained to preclude ponding or erosion. It should be noted that although the
incorporation of the above recommendations should reduce the potential for surficial slope
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instability, it will not eliminate the possibility, and, therefore, it may be necessary to rebuild
or repair a portion of the project's slopes in the future.
8.0 Site Drainage
8.1 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 without the use of impermeable liners or cutoff walls. The site should
be graded and maintained such that surface drainage is directed away from structures in
accordance with 2013 CBC 1804.3, 2016 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.
8.2 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. We
recommend that area drains to collect excess irrigation water and transmit it to drainage
structures or impervious above-grade planter boxes be used. In addition, where landscaping
is planned adjacent to the pavement, we recommend construction of a cutoff wall along the
edge of the pavement that extends at least 6 inches below the bottom of the base material.
8.3 Underground utilities should be leak free. Utility and irrigation lines should be checked
periodically for leaks for early detection of water infiltration and detected leaks should be
repaired promptly. Detrimental soil movement could occur if water is allowed to infiltrate
the soil for a prolonged period of time.
8.4 We understand that individual lot bio-retention basins and other storm water management
devices will be installed. If not properly constructed, there is a potential for distress to
improvements and properties located hydrologically down gradient or adjacent to these
devices. Factors such as the amount of water to be detained, its residence time, and soil
permeability have an important effect on seepage transmission and the potential adverse
impacts that may occur if the storm water management features are not properly designed
and constructed. Based on our experience with similar soil conditions, infiltration areas are
considered infeasible due to the poor percolation and lateral migration characteristics. We
have not performed a hydrogeology study at the site. Down-gradient and adjacent structures
may be subjected to seeps, movement of foundations and slabs, or other impacts as a result
of water infiltration.
Project No. G2054-11-01 - 15 - April 28, 2017
8.5 Storm water management devices should be properly constructed to prevent water infiltration,
a subdrain installed, and lined with an impermeable liner (e.g. high-density polyethylene,
HDPE, with a thickness of about 30 mil or equivalent Polyvinyl Chloride, PVC, liner). The
devices should also be installed in accordance with the manufacturer’s recommendations. The
subdrain should be at least 3 inches in diameter and consist of Schedule 40 PVC pipe. The
subdrain should be properly waterproofed at the edges of the liner where the perforated pipe is
connected to solid pipe. The subdrain should be connected to a proper outlet.
LIMITATIONS
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
make no warranty, express or implied, except that our services were performed in accordance with
engineering principles generally accepted at this time and location.
We will accept no responsibility for any subsequent changes made to the site by others, by the
uncontrolled action of water, or by the failure of others to properly repair damages caused by the
uncontrolled action of water. The findings and recommendations of this report may be invalidated
wholly or partially by changes outside our control. Therefore, this report is subject to review and
should not be relied upon after a period of three years.
Should you have any questions regarding this report, or if we may be of further service, please contact
the undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATE John Hoobs CEG 1524 Shawn Foy Weedon GE 2714
JH:SFW:dmc
(e-mail) Addressee
jOL
TABLE 1
SUMMARY OF FIELD DENSITY TEST RESULTS
Project Name:Project No.:
Pre. No. Re.
1 03/06/17 Lot 12 334 2 0 130.0 9.5 120.1 10.2 92 90
2 03/06/17 Lot 12 337 2 0 130.0 9.5 118.7 11.8 91 90
3 03/07/17 Lot 11 335 2 0 130.0 9.5 117.4 10.9 90 90
4 03/07/17 Lot 11 338 2 0 130.0 9.5 117.2 9.9 90 90
5 03/08/17 Lot 11 340 1 0 126.5 10.0 115.8 10.3 92 90
6 03/08/17 Lot 11 341 2 0 130.0 9.5 118.4 9.5 91 90
7 03/08/17 Lot 12 339 1 0 126.5 10.0 114.3 11.7 90 90
8 03/08/17 Lot 12 341 2 0 130.0 9.5 122.1 10.5 94 90
9 03/09/17 Lot 11 344 1 0 126.5 10.0 115.2 12.5 91 90
10 03/09/17 Lot 12 345 2 0 130.0 9.5 119.8 11.6 92 90
SZ 11 03/10/17 Lot 12 344 1 0 126.5 10.0 114.1 10.8 90 90
SZ 12 03/10/17 Lot 11 345 1 0 126.5 10.0 113.8 11.2 90 90
SZ 13 03/10/17 Lot 11 349 1 0 126.5 10.0 113.9 13.1 90 90
14 03/10/17 Lot 11/12 348 1 0 126.5 10.0 114.7 12.4 91 90
15 03/13/17 Lot 12 347 2 0 130.0 9.5 118.9 10.2 91 90
16 03/13/17 Lot 11 348 2 0 130.0 9.5 119.1 10.0 92 90
17 03/14/17 Lot 12 351 2 0 130.0 9.5 117.8 10.3 91 90
18 03/14/17 Lot 11/12 350 1 0 126.5 10.0 115.6 10.2 91 90
19 03/15/17 Surf Crest Street 1+75 352 3 0 127.8 10.2 116.3 13.1 91 90
20 03/15/17 Lot 11 351 3 0 127.8 10.2 117.0 13.0 92 90
21 03/15/17 Lot 12 351 3 0 127.8 10.2 119.5 12.4 94 90
22 03/15/17 Lot 12 353 3 0 127.8 10.2 117.7 13.2 92 90
23 03/15/17 Lot 11 352 2 0 130.0 9.5 119.8 9.7 92 90
24 03/16/17 Lot 11 354 2 0 130.0 9.5 121.5 10.4 93 90
25 03/16/17 Lot 12 354 2 0 130.0 9.5 118.9 9.8 91 90
26 03/17/17 Lot 12 355 1 0 126.5 10.0 114.3 10.2 90 90
27 03/17/17 Surf Crest Street 0+70 353 1 0 126.5 10.0 115.1 10.0 91 90
28 03/20/17 Lot 11 356 1 0 126.5 10.0 114.7 10.4 91 90
29 03/20/17 Surf Crest Street 0+25 355 1 0 126.5 10.0 114.1 10.9 90 90
30 03/20/17 Lot 10 355 1 0 126.5 10.0 115.0 10.7 91 90
Curve
No.
Test No.
Seascape G2054-11-01
>¾"
Rock
(%)
Max.
Dry
Density
(pcf)
Opt.
Moist
Content
(%)
Field
Dry
Density
(pcf)
Field
Moisture
Content
(%)
Relative
Compaction
(%)
Date
(MM/DD
/YY)
Elev.
or
Depth
(feet)
Location
Required
Relative
Compaction
(%)
~GEOCON
TABLE 1
SUMMARY OF FIELD DENSITY TEST RESULTS
Project Name:Project No.:
Pre. No. Re.
Curve
No.
Test No.
Seascape G2054-11-01
>¾"
Rock
(%)
Max.
Dry
Density
(pcf)
Opt.
Moist
Content
(%)
Field
Dry
Density
(pcf)
Field
Moisture
Content
(%)
Relative
Compaction
(%)
Date
(MM/DD
/YY)
Elev.
or
Depth
(feet)
Location
Required
Relative
Compaction
(%)
31 03/20/17 Lot 10 356 1 0 126.5 10.0 116.1 10.2 92 90
SZ 32 03/20/17 Lot 11 359 1 0 126.5 10.0 110.2 8.4 87 90
SZ 32 A 03/20/17 Lot 11 359 1 0 126.5 10.0 114.1 12.5 90 90
33 03/21/17 Peregrine Place 3+40 346 1 0 126.5 10.0 115.3 10.2 91 90
34 03/21/17 Peregrine Place 3+00 347 1 0 126.5 10.0 116.1 10.2 92 90
35 03/23/17 Lot 6 347 1 0 126.5 10.0 116.8 10.5 92 90
36 03/23/17 Lot 5 338 1 0 126.5 10.0 115.6 10.0 91 90
SZ 37 03/24/17 Lot 6 336 2 0 130.0 9.5 119.0 9.6 92 90
SZ 38 03/24/17 Lot 5 340 1 0 126.5 10.0 114.8 10.5 91 90
SZ 39 03/24/17 Lot 6 339 1 0 126.5 10.0 115.1 10.2 91 90
40 03/28/17 Lot 6 341 1 0 126.5 10.0 113.8 10.4 90 90
41 03/28/17 Lot 5 340 1 0 126.5 10.0 114.2 10.1 90 90
42 03/29/17 Lot 6 343 1 0 126.5 10.0 115.2 10.9 91 90
FG 43 04/11/17 Lot 12 356 2 0 130.0 9.5 122.0 9.9 94 90
FG 44 04/11/17 Lot 11 358 2 0 130.0 9.5 119.9 9.4 92 90
ST 45 04/11/17 N Side Lot 11 360 1 0 126.5 10.0 114.7 9.9 91 90
FG 46 04/11/17 N Side Lot 11 362 2 0 130.0 9.5 120.1 9.2 92 90
FG 47 04/11/17 Lot 6 344 1 0 126.5 10.0 114.3 10.0 90 90
ST 48 04/11/17 Lot 6 341 1 0 126.5 10.0 115.0 10.1 91 90
ST 49 04/11/17 Lot 12 349 2 0 130.0 9.5 118.0 9.1 91 90
ST 50 04/11/17 Lot 12 352 2 0 130.0 9.5 117.4 9.3 90 90
ST 51 04/11/17 Lot 11 354 2 0 130.0 9.5 119.2 9.0 92 90
FG 52 04/20/17 Lot 5 341 2 0 130.0 9.5 120.0 9.1 92 90
53 04/20/17 Lot 10 356 1 0 126.5 10.0 114.7 10.9 91 90
54 04/20/17 Lot 10 357 1 0 126.5 10.0 115.0 10.4 91 90
FG 55 04/24/17 Lot 10 358 1 0 126.5 10.0 115.4 10.2 91 90
~GEOCON
TABLE 1
EXPLANATION OF CODED TERMS
AC Asphalt Concrete IT Irrigation Trench SG Subgrade
AD Area Drain JT Joint Trench SL Sewer Lateral
B Base M Moisture Test SM Sewer Main
CG Curb/Gutter MG Minor Grading SR Slope Repair
DW Driveway MSE Mechanically Stabilized Earth Wall ST Slope Test
ET Electrical Trench PT Plumbing Trench SW Sidewalk
ETB Exploratory Trench RG Regrade SZ Slope Zone
FB Footing Backfill RWL Reclaimed Water Lateral UT Utility Trench
FG Finish Grade RWM Reclaimed Water Main WB Wall Backfill
FS Fire Service SBT Subdrain Trench WL Water Lateral
GT Gas Trench SD Storm Drain WM Water Main
A, B, C, …
R
>¾" ROCK - ROCK CORRECTION
The 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.
TEST NO. PREFIX
TEST NO. RE.
Retest of previous density test failure following additional moisture conditioning or recompaction
Fill in area of density test was removed during construction operations
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
ELEVATION OR DEPTH
Corresponds 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
~GEOCON
Project No. G2054-11-01 April 28, 2017
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 Reddish brown, Silty, fine to medium SAND 126.5 10.0
2 Reddish brown, Silty, fine to medium SAND 130.0 9.5
3 Reddish brown, Silty, fine to medium SAND 127.8 10.2
TABLE III SUMMARY OF LABORATORY EXPANSION INDEX TEST RESULTS ASTM D 4829
Sample No. Representative Lot Nos.
Moisture Content (%) Dry Density (pcf)
Expansion Index
ASTM Soil Expansion Classification
2013/2016 CBC Expansion Classification Before Test After Test
EI-1 10 - 12 8.9 16.0 112.0 3 Very Low Non-Expansive
EI-2 5 and 6 8.9 15.6 111.0 3 Very Low Non-Expansive
EI-3 1 – 4 & 7 - 9 9.2 15.2 113.7 2 Very Low Non-Expansive
TABLE IV SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS CALIFORNIA TEST 417
Sample No. Water-Soluble Sulfate (%) Sulfate Exposure
EI-1 0.023 S0
EI-2 0.033 S0
EI-3 0.020 S0
Project No. G2054-11-01 April 28, 2017
TABLE V SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS SEASCAPE PROPERTY LOTS 1 THROUGH 12
Lot No. Pad Condition Approximate Maximum Differential Fill Thickness (feet)
Approximate Maximum Depth of Fill (feet)
Expansion Index
Recommended Foundation Category
1 Cut Pad -- -- 2 I
2 Cut Pad -- -- 2 I
3 Cut Pad -- -- 2 I
4 Cut Pad -- -- 2 I
5 Undercut Pad 1 6 3 I
6 Undercut Pad 2 10 3 I
7 Cut Pad -- -- 2 I
8 Cut Pad -- -- 2 I
9 Cut Pad -- -- 2 I
10 Fill Pad 1 5 3 I
11 Fill Pad 16 27 3 II
12 Fill Pad 12 21 3 II
TABLE VI SUMMARY OF SITE CLASS SEASCAPE LOTS 1 THROUGH 12
Lot Nos. 2013/2016 CBC Soil Profile Type
1 Through 10 C
11 and 12 D