BRES2014-1166 Geotechnical Update5
Sladden Engineering
45090 Golf Center Parkway, Suite F, Indio, CA 92201 (760) 863-07I3 Fax (760) 863-0847
6782 Stanton Avenue, Suite A, Buena 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 (951) 766-8777 Fax (951) 766-8778
December 29, 2014
Gordon Stein Design
74794 42nd Avenue, Suite 9
Palm Desert, California 92260
Subject: Geotechnical Update
Project: Custom Residence
Meriwether Way - Lot 38B
The Madison Club
La Quinta, California
_ FEB 03 2015
CITY Or LA QUINTA
COMMUNITY DEVELOPMENT
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. 522-4810; 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 to be constructed along Meriwether
Way (identified as Lot 38B) 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 byconventional shallow spread
footings and concrete slabs on grade.
The subject lot was previously graded during the rough grading of the Madison.Club project site.
The rough,grading included recompaction of the native surface soil along with the placement of
engineered fill material to construct the building pad. The site 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 that falls within the previously assumed
building envelope. The building areas 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. Fill material should be placed
in thin lifts at near optimum moisture content and compacted to at least 90 percent relative
compaction.
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December 29, 2014 2- Project No. 544-14325
14-12-486
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 allowab.Ie_.bearing_.pressures:.._recommended._in . the referenced 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.
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: 2013 (CBC) classification criteria. Pertinent 2013 CBC Seismic Design
parameters are summarized below.
Sladden has reviewed the 2013 California Building Code (CBC) and summarized the current
seismic design parameters for the proposed structure. The seismic design category for a structure
may be determined in accordance with Section 1613 of the 2013 CBC or ASCE7. According to the
2013 CBC, Site Class D may be used to estimate design seismic loading for the proposed
structures. The 2013 CBC Seismic Design Parameters are summarized below.
Risk Category (Table 1.5-1): I/Il/III
Site Class (Table 1613.3.2): D
Ss (Figure 1613.3.1):1532.g
S1 (Figure 1613.3.1):0.723g
Fa (Table 1613.3.3(1)):1.0
Fv (Table 1613.5.3(2)):1.5
Sms (Equation 16-37 (Fa X Ss)): 1.532g
Smi (Equation 16-38 (Fv X SI{):1.084g
SDS (Equation 16-39 12/3 X Sms}): IMlg
SDI (Equation 16-40 [2/3 X Smi)):.0.723g
Seismic Design Category: D
December 29, 2014 <3 Project No. 544-14325
14-12-486
We appreciate the opportunity to provide service to you on this project. IE you have any
questions regarding this letter or the referenced reports, please contact the undersigned.
Respectfully submitted, r
SLADDEN ENGINEERING ���pF p
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Brett L. Anderson -,ML--
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Copies: 4/ Gordon Stein Design
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