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( i <br /> 4 ( <br /> . i <br /> � not bc dcsigncd usinc h��drostatic pressures. Por thcsc cimditirnis.thc ��alls shuulJ hc dctiigncd for ' <br /> soil pressurcs. Wc recommend thal thc walls hc dcsigncd using a laicnl soil pressurc c�presscd as <br /> I an equivalcnt iluid dcnsity of 3j pcf(trian�ular distribu�ion). Tliis vahic assumcs no hydroslatic � <br /> pressure bchind thc���alls. <br /> The abo��e-rccommended lateral soil pressurc docs not includc effccls of surchargcs. 14c <br /> � undcrstand that the detention��ault will be dcsigncd for an IiS-20 truckload. llic vault lid and �+alls � <br /> should also bc dcsicned for pressures rcsulting trom ihc o�crlping fill tioils and pa�cmcnt sccti�m. <br /> I We rccommcnd that a surchargc load of 20(1 psf (rcclanculnr disirihuiion) Ix addcd duc In thc f <br /> overlying soil. i <br /> I 4.6.3 Lateral Resistance � <br /> Soil resistancc to lateral foundation loads m;q� bc resisicd hy passive resistance nn ihc sides of <br /> the footings and b�' friction on the base of thc footings. f-or footings supportcd on nativc � <br /> 1 undis[urbed ad��ance ouh��ash sand, thc allmvable Gictional rcsir'3nce ntay be computed using a <br /> coe�cicnt of friction of 0.40 applicd to vcnical dead•load forccs. <br /> i <br /> 1 The allowable passive resistance may be computed using an equi�•alent fluid density of 300 pcf ; <br /> (triangular distribution) if these clements are poured directly against undisturbed nativc soils or I <br /> surroundcd by swctural fill. The sWcturai fill should e�tend out from the face of ihe foundation <br /> Ielement for a distance at least equal to two times the heicht of thc clement and be compacted to �it <br /> least 95 percent of ihe maaimum d ,ry density. <br /> I Tlie above coefficient of friction and passive equi��alent Iluid density��alues incotporale a factor <br /> of safety of about 1.�. <br /> I 4.6.4 Backfill Conditions <br /> � The suitabili�y� of the e�cavated soil for use as backfill of the vault �valis wi11 depcnd on its � <br /> gradauon,moistute content and the weather conditions during construction. Tlie e�isting till fill has � <br /> ( a reiativelp high fines content and are themforc, moisiure-censitive. These soils are suitable for usc � <br /> as backfill pro�•ided that they have a moisture content ncar optimum and can be corupacted ro the <br /> ( requirements provided belo���. If backfill placemen[takes place during wet weather,we recommend � <br /> the use of imported sand and gravel with less than 5 percent fines (material passing U.S. Standard <br /> No. 200 sieve)by���eieht relati��e to the fraction passing the'/.-inch sieve. <br /> ` \yc recomtnend that the�•ault walls be designed �aith a 2-foot-thick laycr of frec-draining sand <br /> � and gravel against the walls, as described in Section 4.5.2 (Drainagel. We also recommend that <br /> I hea��y-gauge galvanized ���ire mesh or a geoteatile filter cloth (Mirafi 140N or equal) be installed <br /> over the weepholes on the back of the wall to prevent migration of soil particles. <br /> All backfill should be compacted to a firm,nonyielding condition. We recommend that backfill <br /> I placed within a horizontal distance cqual to [he height of the wall be compacted to approximately <br /> � 90 to 92 percent of the ma�imum dry density (ASTM D ]557). We rccommend that ilic upper <br /> I2 feet of fill be compacicd to at least 95 percent of the maaimum dry density(ASTIvI D 1557)under <br /> l � <br /> G e o L n g i n c c r s ]( FileNa 75R4-002•00-1130\050101 �/,fc <br /> I /�� <br />