10-0915 (SFD) Geotechnical UpdateUO3
Sladden Engineering
45090 Golf Center Parkway, Suite F, Indio, CA 92201 (760) 863.0713 Fax (760) 863-0847
6782 Stanton Avcnuc, Suitc A, Bucna Park, CA 90621 (714) 523-0952 Fax (714) 523-1369
450 Egan Avenue, Beaumont, CA 92223 (951) 845-7743 Fax (951) 845-8863
800 E. Florida Avenue, Hemet, CA. 92543 (9S 1) 766-8777 Fax (951) 766-8778
November 16, 2010
Discovery Land Company
80955 Avenue 52
La Quinta, California 92253
Subject: Geotechnical Update
Project: Lot 114 B
The Madison Club
La Quinta, California
Project No. 544-10196
10-11-269
Ref: Geotechnical Investigation Report prepared by Sladden Engineering dated January
28,2005; Project No. 544-4810, Report No. 05-01-101
Report of Testing and Observation During Rough Grading prepared by Sladden
Engineering dated March 2,2006; Project No. 5224810; Report No. 06-02-120
As requested, we have reviewed the above referenced geotechnical reports as they relate to the
design and.construction of the proposed custom residence. The project site is located at Lot 114 B
within the Madison Club development in the City of La Quinta, California. It is our
understanding that the proposed residential structure will be of relatively lightweight wood -
frame construction and will be supported by conventional shallow spread footings and concrete
slabs on grade. The project will also include significant site improvements including a swimming
pool and retaining walls within the rear yard areas.
The lot was previously -graded during the initial rough grading of the Madison Club project site.
The rough grading included overexcavation and recompaction'of the native surface soil along
with the placement of engineered fill material to construct the building pads. The rough grading
is summarized in the referenced report of Testing and Observation During Rough Grading along
with the compaction test results.
Because the lot has been previously rough graded, the remedial grading required at this time
should be minimal provided that the building area falls within the previously assumed building
envelope. The building area should be cleared of surface vegetation, scarified and moisture
conditioned prior to precise grading. The exposed surface should -be compacted to a minimum of
90 percent relative compaction prior to fill placement. The previously removed soil and any fill
material should be placed in thin lifts at near optimum moisture content and compacted to at
least 90 percent relative compaction.
November 16, 2010 -2- Project No. 544-10196
10-11-269
The referenced reports include recommendations pertaining to the construction of residential
structure foundations. The previous reports also address the potential for liquefaction,
subsidence and differential settlement. Based upon our review of the referenced reports, it is our
opinion that the structural values included in these reports remain'applicable for the design and
construction of the proposed residential structure foundations.
The allowable bearing pressures recommended in the Geotechnical Investigation report remain
applicable. Conventional shallow spread footings should be bottomed into properly compacted
fill material a minimum of 12 inches below lowest adjacent grade. Additional '.footings
embedment depth will be necessary for the retaining walls proposed along the descending slope.
A minimum lateral distance to daylight of 5 feet should be maintained as measured from the top
of the footings. Continuous footings.should be at least 12 inches wide and isolated pad footings
should be at least 2 feet wide. Continuous footings and isolated pad footings should be designed
utilizing allowable bearing pressures of 1500 psf and 2000 psf, respectively. Allowable increases
of 300 psf for each additional 1 foot of width and 300 psf for each additional 6 inches of depth
may be utilized, if desired. The maximum allowable bearing pressure should be 3000 psf. The
recommended allowable bearing pressures may be increased by one-third for wind and seismic
loading.
Lateral forces may be resisted by friction along the base of the foundations and passive resistance
along the sides of the footings. A friction coefficient of 0.48 times the normal dead load forces is
recommended for use in design: Passive resistance may be estimated using an equivalent fluid
weight of 300 pcf. If used in combination with the passive resistance, the frictional resistance
should be reduced by one third to 0.33 times the normal dead load forces.
The bearing soil is generally non -expansive and falls within the "very low" expansion category in
accordance with the 2007 (CBC)) 'classification criteria. Pertinent 2007 CBC Seismic Design
parameters are summarized on the following'pagc.
Based on our field observations and understanding of local geologic conditions, the soil profile
type judged applicable to. this site is So, generally described as stiff soil. The site is located within
UBC Seismic Zone 4. The following presents additional coefficients and factors relevant to
seismic mitigation for new construction upon adoption of the 2007 California Building Code
(CBC).
Sladden Engineering
November 16, 2010 -3- Project No. 544-10196
10-11-269
The seismic design category for a structure may be determined in accordance with Section 1613
of the 2007 CBC or ASCE7. According to the 2007 CBC, Site Class D may be used to estimate
design seismic loading for the proposed structures. The period of the structures should be less
than 1h second. This assumption should be verified by the project structural "engineer.. The 2007
CBC Seismic Design Parameters are summarized below.
Occupancy Category (Table 1604.5): II
Site Class (Table 1613.5.5): D
Ss (Figure 16135.1):.1.500g
St (Figure 1.61.3.5.1); 0.600g
Fa (Table 16135.3(1)): 1.0
Fv (Table 1613.5.3(2)):1.5
Sms (Equation .16-37 (Fa X Ss)):1.500g
Smi (Equation 16-38 (Fv X Si)): 1.900g
SDs (Equation 16-3912/3 X Srmj) 1.000g
SDI (Equation 16-4012/3 X Smit): 0.6008
Seismic Design Category: D
We appreciate the opportunity to provide service to you on this project, if you have any
questions regarding this letter or the referenced reports please contact the undersigned.
Respectfully submitted,
SLADDEN ENGINEERING_
Brett L. Anderso
Principal Engineer it E*93x2012
1' I
SER/gl
Copies: 4/Discovery Land Company
Sladden Engineering