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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 SER/lh SO Z E m No. C 45389 m F-Ap.9130106 ct �r CIV��- STP OF C ALF Copies: 4/Prest Vuksic Architects Sladderr Engineering r 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