0101-153 (SFD) Geotechnical Reporto
Earth Systems
Southwest 79-811B Country Club Drive
Bermuda Dunes, CA 92201
(760)345-1588
(800)924-7015
FAX (760) 345-7315
January 29, 2001
Christensen Homes, Inc..
45-585 Apache Road
Indian Wells, California 92210
Attention: Mr. Lance Christensen
Subject: Geotechnical Services
Project: Lot 32, La Quinta Golf Estates
48-801 San Dimas Street
La Quinta, California
File No.: 08065-01
01-01-758
As requested, we have reviewed geotechnical engineering reports for projects adjacent to the
subject site for purposes of providing recommendations for site preparation and grading of the
subject site. The site is currently vacant of structures.
The subject lot is located at the south end of San Dimas Street, on the southeasterly side of the
cul-de-sac. The proposed construction will be at or close to the existing elevation of the lot and
will include a one-story single-family residential structure of wood frame type construction with
a stucco exterior: The proposed construction consists of 4,548-ft2 of living area, a 576-ft2 patio,
and a 1,025-ft2 garage. The structure will be supported by conventional shallow continuous
footings and will have interior concrete slabs -on -grade. Other site improvements will include a
pool, spa, concrete driveway and sidewalks, and landscaping.
Site Grading
-Based upon our review of geotechnical reports performed on adjacent properties, it is our
opinion that the site can support the proposed structure. However, the proposed building and
pool areas will require over -excavation and recompaction prior to construction.
The building pad area should be initially prepared by removing any organic growth from the pad
surface. The pad should then be moisture conditioned by the use of sprinklers or rain birds to a
depth of 2 to 3 feet below the current pad grade. If the existing soil is sufficiently moist to
control dust, pre -watering of the site may not be necessary. The building footprint, and to a
distance of 5 feet outside the perimeter, should be over -excavated to a depth of 24 inches below
existing grade or 12 inches below the bottom of the deepest footing. The resulting surface
should be moisture conditioned to at least the optimum moisture content and compacted to a
minimum of 90% relative compaction. If the current pad elevation is to be altered from its
current elevation, non -expansive granular fills should be placed in lifts in maximum 8 -inch lifts
(loose) and compacted to at least 90% relative compaction (ASTM D 1557) near its optimum
moisture content. If the pad is to be lowered in elevation, the depth of moisture conditioning and
over -excavation may need to be increased.
January 29, 2001 2 File No.: 08065-01
01-01-758
Foundations
The structure foundation can be supported on shallow foundations bearing on a zone of properly
prepared and compacted soils as referenced above under Site Grading. The recommendations
that follow are based on very low expansion category soils.
A representative of ESSW should observe foundation excavations prior to placement of
reinforcing steel or concrete. Loose soil or construction debris should be removed from footing
excavations prior to placement of concrete.
Conventional Spread Foundations: Allowable soil bearing pressures are given below for
foundations bearing on recompacted soils as described above. Allowable bearing pressures are
net (weight of footing and soil surcharge may be neglected).
➢ Continuous wall foundations, 12 -inch minimum width and 12 inches below grade:
1500 psf for dead plus design live loads
Allowable increases of 300 psf per each foot of additional footing width and 300 psf for each
additional 0.5 foot of footing depth may be used up to a maximum value of 2500 psf.
➢ Isolated pad foundations, 2 x 2 foot minimum in plan and 18 inches below grade:
2000 psf for dead plus design live loads
Allowable increases of 200 psf per each foot of additional footing width and 300 psf for each
additional 0.5 foot of footing depth may be used up to a maximum value of 2500 psf.
A one-third (1/3) increase in the bearing pressure may be used when calculating resistance to
wind or seismic loads. The allowable bearing values indicated are based on anticipated loads.
Minimum reinforcement for continuous wall footings should be two, No. 4 steel reinforcing bars,
placed near the top and the bottom of the footing. This reinforcing is not intended to supersede
any structural requirements provided by the structural engineer.
Expected Settlement: Estimated total static settlement, based on footings founded on firm soils
as recommended, should be less than 1 inch. Differential settlement between exterior and
interior bearing members should be less than 1/2 -inch.
Frictional and Lateral Coefficients: Lateral loads may be resisted by soil friction on the base of
foundations and by passive resistance of the soils acting on foundation walls. An allowable
coefficient of friction of 0.35 of dead load may be used. An allowable passive equivalent fluid
pressure of 250 pcf may also be used. These values include a factor' of safety of 1.5. Passive
resistance and frictional resistance may be used in combination if the friction coefficient is
reduced to 0.23 of dead load forces. A one-third (1/3) increase in the passive pressure may be
used when calculating resistance to wind or seismic loads. Lateral passive resistance is based on
the assumption that any required backfill adjacent to foundations is properly compacted.
Slabs -on -Grade
Subgrade: Concrete slabs -on -grade and flatwork should be supported by compacted soil placed
in accordance with the Site Grading section of this report.
Vapor Barrier: In areas of moisture sensitive floor coverings, an appropriate vapor barrier
should be installed to reduce moisture transmission from the subgrade soil to the slab. For these
EARTH SYSTEMS SOUTHWEST
January 29, 2001 3 File No.: 08065-01
01-01-758
areas an impermeable membrane (10 -mil moisture barrier) should underlie the floor slabs. The
membrane should be covered with 2 inches of sand to help protect it during construction and to
aide in concrete curing. The sand should be lightly moistened just prior to placing the concrete.
Low -slump concrete should be used to help reduce the potential for concrete shrinkage. The
effectiveness of the moisture barrier is dependent upon its quality, method of overlapping, its
protection during construction, and the successful sealing of the barrier around utility lines.
Slab thickness and reinforcement: Slab thickness and reinforcement of slab -on -grade are
contingent on the recommendations of the structural engineer or architect and the expansion
index of the supporting soil. Based upon our findings, a modulus of subgrade reaction of
approximately 200 pounds per cubic inch can be used in concrete slab design for the expected
very low expansion subgrade.
Concrete slabs and flatwork should be a minimum of 4 inches thick. We suggest that the
concrete slabs be reinforced at slab mid -height to resist cracking. Concrete floor slabs may
either be monolithically placed with the foundations or doweled after footing placement. The
thickness and reinforcing given are not intended to supersede any structural requirements
provided by the structural engineer. The project architect or geotechnical engineer should
continually observe all reinforcing steel in slabs during placement of concrete to check for proper
location within the slab.
Control Joints: Control joints should be provided in all concrete slabs -on -grade at a maximum
spacing of 36 times the slab thickness (12 feet maximum on -center, each way) as recommended
by American Concrete Institute (ACI) guidelines. All joints should form approximately square
patterns to reduce the potential for randomly oriented, contraction cracks. Contraction joints in
the slabs should be tooled at the time of the pour or saw cut (1/4 of slab depth) within 8 hours of
concrete placement. Construction (cold) joints should consist of thickened butt joints with one-
half inch dowels at 18 -inches on center or a thickened keyed joint to resist vertical deflection at
the joint. All construction joints in exterior flatwork should be sealed to prevent moisture or
foreign material intrusion. These procedures will reduce the potential for randomly oriented
cracks, but may not prevent them from occurring.
Curing and Quality Control: The contractor should take precautions to reduce the potential of
curling of slabs in this and desert region using proper batching, placement, and curing methods.
Curing is highly affected by temperature, wind, and humidity. Quality control procedures may
be used including trial batch mix designs, batch plant inspection, and on-site special inspection
and testing. Typically, for this type of construction and using 2500 -psi concrete, many of these
quality control procedures are not required.
Mitigation of Soil Corrosivity on Concrete
Chemical analyses for corrosivity testing of the native soils has been conducted on adjacent lots
and were found to have very low sulfate ion and chloride ion concentrations. Sulfate ions can
attack the cementitious material in concrete, causing weakening of the cement matrix and
eventual deterioration by raveling. Chloride ions can cause corrosion of reinforcing steel. The
Uniform Building Code does not require any special provisions for concrete for these low
concentrations as tested. Normal concrete mixes may be anticipated for used. However, a
sample of the native soil should be .obtained at the completion of rough grading to evaluate
corrosive potential of the upper 12 inches of finish grade.
EARTH SYSTEMS SOUTHWEST
January 29, 2001 4 File No.: 08065-01
01-01-758
A minimum concrete cover of three (3) inches should be provided around steel reinforcing or
embedded components exposed to native soil or landscape "water (to 18 inches above grade).
Additionally, the concrete should be thoroughly vibrated during placement.
Electrical resistivity testing of the soil suggests that the site soils may present a severe potential
for metal loss from electrochemical corrosion processes. Corrosion protection of steel can be
achieved by using epoxy corrosion inhibitors; asphalt coatings, cathodic protection, or
encapsulating with densely consolidated concrete. A qualified corrosion engineer should be
consulted regarding mitigation of the corrosive effects of site soils on metals.
Seismic Design Criteria
This site is subject to strong ground shaking due to potential fault movements along the
San Andreas and San Jacinto Faults. The minimum seismic design should comply with the latest
edition of the Uniform Building Code (UBC). The UBC provisions are generally intended to
protect human life safety and prevent structural collapse. It is not necessarily intended to prevent
structural damage or preserve functionality after a large earthquake. Therefore, more stringent
seismic design should be considered if a particular level of structural performance is desirable
after a large earthquake. That design should be based on a site and project specific seismicity
analysis. The following are updated 1997 UBC seismic design values:
1997 UBC Seismic Coefficients for Chapter 16 Seismic Provisions
The potential for soil liquefaction to occur at this site is considered negligible because the depth
of groundwater beneath the site exceeds 50 feet. In addition, the project does not lie within the
Riverside County liquefaction study zone.
Closing
This report is issued with the understanding that the owner, or the owner's representative, has the
responsibility to bring the information and recommendations contained herein to the attention of
the architect and engineers for the project so that they are incorporated into the plans and
specifications for the project. The owner, or the owner's representative, also has the
responsibility to take the necessary steps to see that the general contractor and all subcontractors
follow such recommendations. It is further understood that the owner or the owner's
representative is responsible for submittal of this report to the appropriate governing agencies. .
EARTH SYSTEMS SOUTHWEST
Reference
Seismic Zone:
4
Figure 16-2
Seismic Zone Factor, Z:
0.4
Table 16-I
Soil Profile Type:
Sp
Table 16-J
Seismic Source Type:
A
Table 16-U
Closest Distance to Known Seismic Source:
11.0 km = 6.8 miles
(San Andreas Fault)
Near Source Factor, Na:
1.00
Table 16-5
Near Source Factor, Nv:
1.16
Table 16-T
Seismic Coefficient, Ca:
0.44 = 0.44Na
Table 16-Q
Seismic Coefficient, Cv:
0.74 = 0.64Nv
Table 16-R
The potential for soil liquefaction to occur at this site is considered negligible because the depth
of groundwater beneath the site exceeds 50 feet. In addition, the project does not lie within the
Riverside County liquefaction study zone.
Closing
This report is issued with the understanding that the owner, or the owner's representative, has the
responsibility to bring the information and recommendations contained herein to the attention of
the architect and engineers for the project so that they are incorporated into the plans and
specifications for the project. The owner, or the owner's representative, also has the
responsibility to take the necessary steps to see that the general contractor and all subcontractors
follow such recommendations. It is further understood that the owner or the owner's
representative is responsible for submittal of this report to the appropriate governing agencies. .
EARTH SYSTEMS SOUTHWEST
January 29, 2001 5 File No.: 08065-01
01-01-758
Earth Systems Southwest (ESSW) has striven to provide our services in accordance with
generally accepted geotechnical engineering practices in this locality at this time. No warranty
or guarantee is express or implied. This report was prepared for the exclusive use of the Client
and the Client's authorized agents.
ESSW.should be provided the opportunity for a general review of final design and specifications
in order that earthwork and foundation recommendations may be properly interpreted and
implemented in the design and specifications. If ESSW is not accorded the privilege of making
this recommended review, we can assume no responsibility for misinterpretation of our
recommendations.
This report is based on the assumption that an adequate program of client consultation,
construction monitoring, and testing will be performed during the final design and construction
phases to check compliance with these recommendations. Maintaining ESSW as the
geotechnical consultant from beginning to end of the project will provide continuity of services.
The geotechnical engineering firm providing tests and observations shall assume the
responsibility of Geotechnical Engineer of Record.
Should you have any questions concerning our report please give us a call and we will be pleased
to assist you.
�OFESS;p
Sincerely, S. N9!
EARTH
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EARTH SYSTEMS SOUTHWEST
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Reference: USGS Topographic Map, Figure 1 - Site Location Map
La Quinta Quadrangle, 1980 (photorevised)
Lot 32, La Quinta Golf Estates, 48801 San Dimas, LQ, CA
File No.: 08065-01
N Scale: 1" = 2,000' , Earth Systems
0 2,000 4,000 Southwest
Figure 2 - Site Map
Lot 32, La Quinta Golf Estates, 48801 San Dimas, LQ, CA I
File No.: 08065-01
Earth Systems
Southwest