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BRES2015-0110 Geotechnical Update0 45090 Golf Center Parkway, Suite F, Indio, CA 92201 (760) 863-0713 Far_ (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 February 23, 2015 Christopher McFadden Architect 74-145 St. Charles Place, Suite 4 Palm Desert, California 92211 Project: Proposed Smith Residence 80-790 Via Montecito The Hideaway La Quinta, California Subject: Geotechnical Update RECEIVED DEC 2 2 2015 CITY OF LA GIUINTA COMMUNITY DEVELOPMENT Project No. 544-15044 15-02-089 MAR 3 12015 CITY OF Lai QUINTA COMMUNITY DEVELOPMENT Ref: Geotechnical Engineering Report prepared by Earth Systems Southwest (ESSW) dated September 22,2000; File No. 07117-10, Report No. 00-09-772 Report of Testing and Observation During Rough Grading prepared by ESS dated August 28,2002; File No. 07117-11, Report No. 01-07-718 Report of Testing and Observation During Rough Grading, prepared by Sladden Engineering dated October 12, 2003; Project No. 544-2199 Repor_ No. 03-10-647 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 80-790 Via Montecito within the Hideaway Golf Club development in the City cf La Quinta, California. It is our understanding that the proposed residence will be a relatively 4.ghtweight wood -frame structure supported by conventional shallow spread footings and concrete slabs on grade. The subject lot was previously graded during the rough grading of the Hideaway project site and was subsequently regraded. The rough grading included over -excavation of the native surface soil along with the placement of engineered fill soil to construct the building pads. The regrading included processing the surface soil along with minor cuts and fills to construct the individual building pads to the current configurations. Some additional over -excavation was performed in areas where the building envelopes were reconfigured. The most recent site grading is summarized in the referenced Report of Testing and Observations During Rough Grading prepared by Sladden Engineering along with the compaction test results. The referenced reports include recommendations pertaining to the construction of residential structure foundations. Based upon our review of the referenced reports, .t is our opinion that the structural values included in the referenced grading report prepared by SIadden Engineering remain applicable for the design and construction of the proposed residential structure foundations. Sladden Engineering ;;_, February 23, 2015 -2- Project No. 544-15044 15-02-089 Because the lot has been previously rough graded, the remedial grading required at this time should be minimal provided that the building falls within the previously established 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 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. The allowable bearing pressures recommended in the referenced 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 11500 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 0.50 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 non -expansive and falls within the "very low" expansion category in accordance with 2013 California Building Code (CBC) classification criteria. Slab thickness and reinforcement should be determined by the structural engineer. We recommend a minimum floor slab thickness of 4.0 inches. All slab reinforcement should be supported on concrete chairs to ensure that reinforcement is placed at slab mid -height. Slabs with moisture sensitive surfaces should be underlain with a moisture vapor retarder consisting of a polyvinyl chloride membrane such as 10 -mil Visqueen, or equivalent. All laps within the membrane should be sealed and at least 2 inches of clean sand should be placed over the membrane to promote uniform curing of the concrete. To reduce the potential for punctures, the membrane should be placed on a pad surface that has been graded smooth without any sharp protrusions. If a smooth surface can not be achieved by grading, consideration should be given to placing a 1 -inch thick leveling course of sand across the pad surface prior to placement of the membrane. 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 following presents additional coefficients and factors relevant to seismic mitigation for new construction based upon the 2013 California Building Code (CBC). February 23, 2015 -3- Project No. 544-15044 15-02-089 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 mEy be used to estimate design seismic Ioading for the proposed structures. The 2013 CBC Seismic Design Parameters are summarized below. Risk Category (Table 1.5-1): I/II/III Site Class (Table. 1613.3.2): D Ss (Figure 1613.3.1):1.500g Sl (Figure 1613.3.1): 0.684g Fa (Table 1613.3.3(1)): 1.0 Fv (Table 1613.5.3(2)):1.5 Sms (Equation 16-37 (Fa X Ss]): 1.500g Sm1 (Equation 16-38 (Fv X S11): 1.026g SDS (Equation 16-39 (2/3 X Sms]):1.000g SD1 (Equation 16-40 [2/3 X Sml)): 0.684g Seismic Design Category: D If you have questions regarding this letter or the referenced report:a, please contact the undersigned. Respectfully submitted, SLADDEN ENGINEET Brett L. Anders n Principal Engineer iJ f'do. C45t;9 r --%P. 9!30116 SER/gvm civil EIVGNVEERII'MvCAO T Copies: 4 / Addressee Sys/-- /5-a5'�! A QUINT A Pidase verify that soils reports contain all of the above Information. In additlon, to assure continuity between•the investigation/reporting stage and the execution stage, please use the following checklist to verify that the conclusions and recommendations in the report corer all the required -elements. Only then- can we be assured that the construction documents address all of the site soil conditions, .La Quinta Geotechnical Report Checldist Does the "Conclusions and Recommendations" section of the sport address each of the following criteria? "Address" means; (a) the Criterion is considered significant and mitigation-neasure(s) noted, .or; (b) the criterion Is considered insighificant and explicitly so stated. Y9s No Criterion ® Foundation criteria to mitigate the effects of expansive soils, ® Foundation criteria based upon bearing capacity. -of -iatural or -compacted soil. . ® Foundation criteria to mitigate the effects of liquefaction. ® Foundation criteria• to mitigate the effgcts of seismically Induced differential settlement, E3 Foundation criteria to mitigate the effects of long-term differential settlement. � ® .. Foundation, crlterta._to .mitigate, the.effects.of.varying soli strength. . ® Foundation criteria to mitigate expected total and deferential settlement, Any "No" answers to the -above checklist should be noted as specific required COf l ections,