05-5557 (SFD) Geotechnical UpdaterR
r.
Sladden -Engineering
6782 Stanton Ave., Suite A, Buena Park, CA 90621 (714)52370952 Fax (714) 523-1369
39-725 Garand Ln., Suite G, Palm Desert, CA 92211 (760) 772-3893 Fax (760) 772-3895
February 17, '2006
Prest Vuksic Architects
44-530 San Pablo Avenue, Suite 200
Palm Desert, California 92260
Project: 78-241 Deacon Drive West
The Tradition
La Quinta, California
Subject: Geotechnical Update
Project No. 544-06141
06-02-165
Ref: Report of Testing and Observation During Rough Grading prepared'.by Sladden
Engineering dated July 30, 1997; Project No. 522-6138G1
Geotechnical Update prepared by Sladden Engineering dated December 12, 1996;
Project No. 444-6130
As requested, we have. reviewed the above referenced geotechnical reports as they relate to the
design and construction of the proposed single family residence. The project site is identified as.
Lot 23 along Deacon Drive within The Tradition Golf Club development in the City of La Quinta,
California. It is our understanding that the proposed residence will be a relatively lightweight
wood frame structure supported -by conventional shallow spread footings and concrete slabs on
grade.
The lot was .previously graded during'the rough grading of The Tradition project site. The rough
grading included overexcavation of the. native surface soils along with the placement of
engineered fill material to construct.the building pads. The site grading is summarized in the
referenced Report of Observation and Testing during Rough Grading along with the compaction
test results.
February 17, 2006 -2- Project No. 5.44-06141
06-02-165
The referenced reports include recommendations pertaining to the construction of residential
structure foundations. Based upon our review of the referenced reports, it is our opinion that. the
structural values included in the referenced grading report remain applicable for the design and
construction of the proposed residential structure foundations.
Because the lot has been previously rough graded, the remedial grading required at this time
should be minimal. The building area should be cleared oe f surface vegetation, scarified and
moisture conditioned prior to precise grading. The exposed surface should be compacted so that
a minimum of 90 percent relative compaction -is attained, prior to fill placement. Any fill material
should be placed in thin lifts at near optimum moisture content and compacted. to at least 90
percent relative compaction.
Allowable Bearing Pressures: The allowable bearing pressures recommended in the grading
report prepared by Sladden Engineering 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. An
allowable increase 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.
The bearing soils are non -expansive and fall within the "very low" expansion category in
accordance with Uniform Building Code (UBC) classification criteria. Pertinent 1997' UBC
Seismic Design parameters are summarized on the attached data sheet.
If you have questions regarding this letter or the referenced report, please contact the
undersigned.
Respectfully submitted,
SLADDEN ENGINEERING OFEssroy
Brett L. Anders6n
Principal Engineer
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Copies: 4/Prest Vuksic Architects
Sladderr Engineering
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February 17, 2006
-3-
1997 UNIFORM BUILDING CODE INFORMATION
Project No. 544-06141
06-02-165
The International Conference of Building Officials 1997 Uniform Building Code contains .
substantial revisions and additions to the earthquake engineering section in Chapter. 16.
Concepts contained in the code that will be relevant to construction of the proposed structure are
summarized below.
Ground shaking is expected to be the primary hazard most likely to affect the site, based upon
proximity to significant faults .capable of generating large earthquakes. Major fault zones
considered to be most likely to create strong ground shaking at,the site are listed below.
Fault Zone
Approximate Distance
From Site
Fault Type
(1997 UBC)
San Andreas
12.0 km
A
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 or dense soil. The site is
located within UBC Seismic Zone 4. The following table presents additional coefficients and
factors relevant to seismic mitigation for new construction upon adoption of the -1997 code.
Sladden Engineering
Near -Source
Near -Source
Seismic
Seismic
.Seismic
Acceleration
Velocity
Coefficient.'
Coefficient
Source
Factor, Na_
Factor, N�
Ca
C�
San Andreas
1.0
1.12
0.44'Na
0.64 N�
Sladden Engineering