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BRES2015-0302 Geotechnical Update"I. Engineering 45090 Golf Center Parkway, Suite F, Indio, CA 92201 (760) 863-0713 Fax (760) 863-0847 6782 Stanton Avenue, Suite C, 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 August 10, 2015 Gordon Stein Design 74794 42^ 1 Avenue, Suite 9 Palm Desert, California 92260 Subject: Geotechnical Update Project: Proposed Custom Residence The Madison Club — Lot 66B La Quinta, California Project No. 54445187 15-08-329 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 to be constructed on Lot 66B 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 subject lot was previously graded during the rough grading of the Madison Club project site. The rough grading included over -excavation and recompaction 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 that falls within the previously assu ped__. building envelope. The building areas should be cleared of surface yei ptat on !kp �?� � _� moisture conditioned prior to precise grading. The exposed suji rfaces lld"� n;lpkctrgd` o 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 rstc`Iand compacted to at least 90 percent relative compaction. NCB Sladden Engineering August 10, 2015 -2- Project No, 544-1.5187 15-08-329 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 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. 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 on the following page. 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 1.604.5):1/11/111 Site CIass (Table 1613.3.2): D Ss (Figure 1613.3.1):1.502g S1 (Figure 1.613.3.1): 0.702g Fa (Table 1613.3.3(1)): 1.0 Fv (Table 161.3.5.3(2)): 1.5 Sms (Equation 16-37 (Fa X Ss)):1.502g Sm1 (Equation 16-38 (Fv X S1.1):1.053g SDS (Equation 16-39 12/3 X Snis)): 1.001g SD1 (Equation 16-40 (2/3 X Smi1): 0.702g Seismic Design Category: D Madden Engineering August 10, 2015 -3- Project No. 544-15187 15-08-329 In addition, we have sampled the surface soil on the subject lot to determine the soluble sulfate content as it relates to selecting appropriate concrete mix designs. Testing indicates that the site soil is generally considered corrosive with respect to concrete. The testing indicated soluble sulfate content of 6400 ppm (0.640 percent) that corresponds with the " severe" exposure category in accordance with ACT 318-08, Table 3. Based upon this, the use of sulfate resistant concrete mixes will be required. Structural concrete in contact with the soil should have a minimum compressive strength of 4000 psi and a maximum water -cement ratio of 0.50. 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 Brett L. Anderson Principal Engineer ENGIrl -ERIi ?G SER/gvm Copies: 4/Gordon Stein Design Slarlden Engineering 51-1M-1619'� Please verify that soils reports contain all of the above information. In addition, 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 cover 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 Checklist Does the °Conclusions and Recommendations" section of the report address each of the following criteria? "Address" means: (a) the criterion is considered significant and mitigation measure(s) noted, or; (b) the criterion is considered Insignificant and explicitly so stated. Yes . No Criterion ❑ Foundation criteria based upon bearing capacity of natural or compacted soil. ❑ Foundation criteria to mitigate the effects of expansive soils. j ❑ Foundation criteria based upon bearin capacity. of natural / g _ or compacted soil. ❑ Foundation criteria to mitigate the effects of liquefaction. 711 ❑ Foundation criteria to mitigate the effects of seismically, Induced differential settlement. ❑ Foundation criteria to mitigate the effects of long-term differential settlement. ❑ Foundation criteria to mitigate the effects of varying soil strength. ❑ Foundation criteria to mitigate expected total and differential settlement. Any "No" answers to the .above checklist should be noted as specific required corrections. r TABLE 19-A-2—REQUIREMENTS FOR SPECIAL EXPOSURE CONDITIMIS MINIMUM MAXIMUI I • WATER:CE1MEftTR'IOUS 10!'k� NORMAL'-WEAND . LJGH fS'lEIGKF. - MATERlAL9, RAho;'BY::' AGGREGATI •CONCRETE, EXPOSURE CONDMON •WEIGHT,'NORMAL:WEIGHT• AGGREGATE CONCRETE • x a,t10689.tor 6iPa Concrete intcndcd to have low permeability when exposed to water 0.50 4,000 Conere)a exposed to*freezing and thawing in a moist condition or to deicing chemicals 0.45 4,500 ' For Corrosion projection for reinforced concrete exposed to chlorides from deicing ncmicals, salts or brackish:watcr, orsprayftnm these "sources 0.40 S,OOG TABLE 19-A-3--REQUIREMENTS•FOFJ CONC13ET-E EXPOSED TO SULFb.TE•-CONTAI),llNr:-cnt:t IrtnmQ NORMAL -WEIGHT UrHME1GHT AGGREGATE AGGREGATE =CONCRETE - Mazlmvm'Watar- CementlUou: 1, •Normal- Velptt[•and WATEP SOLUBLE SULFATE l tdtarlalta ReUo,-by:. 11Qhtwdpht ' SULFATE So) IN SOtt� P RG AGE BY We{Qhts..� !'tOA ADOro$lite.1 CO°te,,ps! EXPOSURE WEJGHY , SULFATE(SO4)IF{ WATER, pprn. CEMENTTYPE eht' Concrete S x G.6psagTorMPa. Negligible O.DG-4.10 Maderatc2• 1).1M20 150 1 500 11. IPCMS), iS OSO 4,000 (MS) Sevcrc 0.2Q 2 00 I SDO 1'G,OOG V 0.45 4,500 Very mvem Over 2.GG Ovcr 10,DOG V plus 0.45 4,500 - - pozzolan3 I A . u �� iu�rcc sclrngm may ocicquucd for low permeability-or forprotcction Z against wrrosion'of embEddcd items or frcczing and thawing (fabl'_ 19=A-2)_ Seawater_ ?PO=Olan that has been determined by test or service record to imprnvc sulfa tautmg'I pc V ccmcnL ct resistance when usqcl in concrete con- 2-264 Slac9den Engineering 6782 Stanton Ave., Suite A, Buena Park, CA 90621 (714) 523-0952 Fax (714) 523-1369 45090 Golf Center Pkwy, Suite F, Indio, CA 92201 (760) 863-0713 Fax (760) 863-0847 450 Egan Avenue, Beaumont, CA 92223 (951) 845-7743 Fax (951) 845-8863 Date: August 6, 2015 Account No.: 544-15187 Customer: MOX Design Location: Madison Club, Lot 6613, La Quinta Sulfate Series Analytical Report Soluble Sulfates per CA 417 PPM 6400 Soluble Chloride per CA 422 pprn :Ii Sulfate 544-15187 080615