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August IR,20U4 <br />Mr. Jim "I hom:is <br />13clvcJcrc Lols 3? anJ i_1 <br />L&A .Icb N�. 4AORi� <br />Pagc I S <br />13ASP:MF.N"1' ANU RI�I'AINING �1'ALI.S <br />fSascmcnt w.ills « slr.iineJ horizonlally al �hc lop arc considcrcJ unyiclding and shuuld bc <br />dcsigncd for a I�tcral suil pressurc undcr ihc at-rest cundition; whilc rctaining walls frec lo inuvc <br />al thc iop slioidJ bc dcsigncd I'ur aGivc lalcral soil pressurc. Wc rccommcnrl Ihat a latcral soil <br />pressure of 55 pcf GPD be uscd lor thc design of foimdation walls restrained at Ihe lop; and 40 <br />pcf L•:PD for retaining walls unrestraincd at the top. "I�o counter the aclive soil or at-rest pressure, <br />a passive lateral soil pressure of 350 pcf GFD may be uscd, except thal the passive pressure <br />within the �op 12 inches of �he �inish subgrade should be ignored. l'he above laleral soil <br />presswes are undcr �hc assumption lhal gruunclwatcr bchind the walls is fully drained. lb resist <br />against sliding, ihe I�iction lorce bet���ecn the footings and the subgrad� soils may be calculated <br />hascd on a cocflicieni nf friclion of 0.G0. The above soil ��arameters are ullimn�e values, and <br />properlaclors ol salcly should bc uscJ in thc dcsign ol thc basemcnl and retaining wulls against <br />sliding and overturning failures. !?asc�nent walls or rctaining walls may be supported on footing <br />foundations seated on or in�.i the underlying, vcry-stiff to hard silt or �he dense to ven-dense <br />lisper,uicr San�l �cpusits, ��ith an allowablc suil hcaring pressurc not Io cxcccd 2,500 psf. <br />A vcrtical dnina�tc bl:inkct consisling uf al Icasi I?-indi-thick frec-draining pca �ravcl o: washcd <br />gravcl shuuld hc �ilaccd on thc upslo��c sidc uf I��undaiion and rctaining walls lo prevcnt <br />accumul:iliun uf gruundwalcr bchinJ ancl buildup of hydrostatic pressurc againsl thc walls. l�he <br />drainagc blankcl should hc ol a cican, frcc-draining, granular malerial, containing no morc than <br />J'SL hy �+cight of fines passing lhe No. 200 sicve, based ou the fraction passing the No. 4 sieve. <br />I'his Gce-draining h:ick�ill shuuld be compacted Io the minimum dry density recommended in <br />S_1 KUC�I�UIt/�I. fll L scr,ion nf this report. 'fhc top 12 inches of backlill should consist of <br />compacled, on-site soils. The backfill material for the foundation and retaining walis should be <br />cumpacted wilh a hand-operated compaclor. lieavy compaction equipntenl should not be <br />all�i�vcd closcr to Ihc �valls lh�n a horir.untal distance cyual to thc wall hcights. A fooling drain, <br />LIU & ASSOCIATES, INC. <br />