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BRES2020-0217 - Soils ReportSladden Engineering 9 9 45090 Golf Center Parkway, Suite F, Indio, CA 92201 (760) 863-0713 6792 Stanton Avenue, Suite C, Buena Park, CA 90621 (714) 523-0952 450 Egan Avenue, Beaumont, CA 92223 (951) 845-7743 w .Sladdenengineeringxom September 9, 2020 Project No. 544-20284 20-09-453 Mr. Richard Doan P.O. Box 8011 Rancho Santa Fe, California 92067-8011 Subject: Geotechnical Update Project: Proposed Custom Residence 81333 Peary Place - Lot 59A The Madison Club La Quinta, California 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 In accordance with your request, we have reviewed the above referenced geotechnical reports as they relate to the design and construction of the proposed custom residence to be constructed on Lot 59A located at 81333 Peary Place 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 referenced reports include recommendations pertaining to the design and 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 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. Sladden Engineering September 9, 2020 -2- Project No. 544-20284 20-09-453 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 2019 (CBC) classification criteria. Slab thickness and reinforcement should be determined by the Project Structural Engineer. We recommend a minimum floor slab thickness of 4.0 inches and minimum reinforcement of #3 bars at 24 inches on center in both directions. 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 cannot 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. The seismic design category for a structure may be determined in accordance with Section 1613 of the 2019 CBC or ASCE7-16. According to the 2019 CBC, Site Class D may be used to estimate design seismic loading for the proposed structures. The 2019 CBC Site Specific Seismic Hazard Analyses are attached. The subject lot was previously graded during the rough grading of the Madison Club project site. The rough grading included over -excavation and re -compaction of the native surface soil along with the placement of engineered fill material to construct the building pads. 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 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. 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. Sladden Engineering September 9, 2020 -3- Project No. 544-20284 20-09-453 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 SSlpy' ��C ERrNc `moo BRED I" �G' w J. COHRT 0 DERSOAf Brett L. Ande No, 369 Matthew. Cohrt Principal Enginee a CIVIL Principal Geologist 2634 � ENGINEERfNG � J s�. ���F SER/ra �9 OF (A� �F�C? OF CA'0F Copies: Q Mr. Richard Doan Shulden Engineering Please verify that soifq reports contain all of the abovo Information. In addition, to assure continuity between the Invastigationlreporting stage and the execution stage, please use the following checklist to vcdfy that the conclusions and recommendations in the report cover all the required elements, Only then can we be assured that the construction documents address all of fie site soil conditlons. La Qulnta Geotechnical Report Checklist Does the "Conclusions and Recommendations" -section of the report address each of the follovring criteria? "Address" means: (a) the criterion Is considored significant and mitigation measure(s) noted, or; (b) the criterion is consfdamd insignificant and explicitly so stated. Y No criterion ❑ Foundation criteria based upon t)enring capacity of natural or compacted soil. 0� Ct Foundation criteria to mitigate the effects of expansive soils. is ❑ Foundation criteria based upon bearing capacity, of natural or compacted soil. ❑ Foundation criteria to rnitigato.the erects of liquefaction. L1 ❑ Foundation criteria to mitigato the effects of seismically induced differential settlement. U © Foundation criteria to mitigate the effects of long-term differential settlement U ❑ Foundation criteria to mitigate the effects of varying soil strength. 0 Foundation criteria to mitigate O*Octed total and differential settlement. Any "No" answers to the -above checklist should be noted as specific required corrections. -�ERSOiV tip N . 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