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. ._._ .__ _.. _ _ . .. . . . . . . ._.. _ _ _ . ._ _ ..._ ,._.. . , .�_ �_ _ _ , . __ <br /> Glemti•ood 7'cmcc <br /> filc Numbcr 12G994 <br /> May 12, 1994 <br /> Page 17 <br /> We reconunend Uiat a laternl passive soil pressure of 100 pounds per cubic foot (PCr) be used in dcsign. <br /> The pressure should be a;plicd starting at 6 inches bclwv the planned subgrnde elevation to allow for some <br /> sctticment of the undcrlying 611. 71us value includes a factor of safety of 1.5. <br /> An altcrnativo mcthod lhat would incre�se the allowable passivc pressure is to excavate the cxisting soil <br /> arow;d Uic outside of Uie plaruicd foundation and replace it with structural fill. The ercavation should <br /> extead out from the pile cap a distance eyual to lhree times the dcpth of the pile cap. W ith Ihis system, we <br /> recommend U�at a later�l passive soil pressure of 200 pounds per cubic foot (PCF)be used in dcsign. 'Ihe <br /> pressure should bc applied starting at 6 inchcs bclow the plan:ied subgtade elevation to allow for some <br /> sc�dcmcnt ofd�c undcrlying fill. 'Iliis valuc includes a faclor ofsafcty cf 1.5. <br /> Retaining�Valt� <br /> Thc latcral pressure acting on rctaining walls is dependcnt on Qie naturc and density of thc soil behind du <br /> wall, the amount of lateral wall movement µ•hich can occur as backfill is placed, and the inclination of die <br /> backfill. For walls that nre frce to yield at thc top at Icast one U�ousandth oC the I�eight of thc wall, soil <br /> pressures will be less Uian if movement is limitcd by such fnctors as wall stilFncss or bracing. We <br /> recommcnd that yiclding�valls supporting horizonGll backfill be dcsigned using :ui cquivalent (luid density <br /> of 35 pounds per cubic foot (PFC), whilc non-yielding walls be designcd using an equivalcnt Ouid Aensity <br /> of 55 PFC. 'llic nbove recommcndcd lateral soil pressurcs do not includc thc effccts of surch�rges such as <br /> traRic loads or othcr surface lo.�+ds. Surcharge efTccts sliould be considered, if approprinte. <br /> "Ilic nbove latctal pressures may be resisted by Giction at the base of Uw �vall and plssivc pressure ngainst <br /> llie foundation. Thc values providcd in thc Foundntion subscction of this report for passivc pressure and <br /> friction should bc uscd. <br /> All backfill for subgrade�valls should wnsist of cican fill «�ithout organic and bc compacicd to behvecn 90 <br /> and 92 percent of lhe maximum dry density dctertnincd in accordancc with ASTM D 1557. Care should bc <br /> G�kcn to prevent tlic builJup oC exccss latcral soil pressures duc to overcompnction of thc backfill behind <br /> tlic��•all. 1'his c.1n be accomplishcd by placing Q�e bnckfill locatcd«�Ihin 18 to 24 ineLes of thc wnll in IiAs <br /> not excccding 8 inchcs in loosc tl�icl:ness and compacting diis zone «�th Land opcnted vibrating plate <br /> compactors. <br /> 1'cnnmicnt drninage systems should be inst��lled for subgrndc walls. Wc rcconvncnd that thcsc dninagc <br /> s�stems consisl of I8 inches of cle.�n (Iess that 3 percent fines), free<Iraining gr;uudar material placed <br /> along thc back of tl�e wall. 71ie graimlar matcrial should be placed up dic back oCdia���all to ���thin t foot <br /> of Aic ground surfacc. A less pemieablc soil should be placed in llic last 1 foot. �lotted drainpipc having a <br /> NELSON-COUVRETTE�ASSOCIATES, INC. <br /> rr_R-2-.-���r i2: it 2nr nst 25io 96: P.19 <br />