2408 RAVENNA ST 2016-01-01 MF Import

� ( � Lowell Short Plac ' ' 7une 2, 1999 NCA File No. 3594Sy Page 9 2-inch-thick ssnd blanket may be used to cover the vapor barrier to sid in curing the concrete. The c3pillary brral:material should be conaected to tha footing drsins to provide positive dninage. Lateral Preseures The latera! earth pressure acting on rateining wells is dependent on the natute end density of the �oil behiad the wait, the amoant of lateral wall movement, which can oecur es bacl�ill is pleced, mld the inclination of the backfill. WaUs that ero fise to yield at least one-thousan�ith of the height of the wall are in an "nctive" condiNon. Walls ratrained from movanent by stiffness or bracing are in an "at-resP' condition. Active earth pressure and at-isst earth prwsure ean be calculated based on equivaleat fluid density. Fyuivalen.fluid �lensides for active and at-�est eaith pieasure of 35 pounds per cubic foot(p:fl and 55 pef,respectively,may be used for dexign for a level beckslope wheie we�l baekfill is eompacted to at least 90 pereent of maximum dry density by AS7M D 1557. Thcse values assume that ibe on-site eands or granular import soils ate used for bacicfill,and thet the wall b:.ek�ll is drained. The pieeeding valuGs do not include the effects of suroharges; such es due to foundation losds, traftic, or other surface loads. Surchazge effects should be consideted whero appropriate. The lateral pressures may be resisted by friction et the base of the wap and pasaive resistance against the subswface portioas of the fuu�etlon. A coeffici�nt of&ietion of 0.4 may be used to calculatr.Yhe bau friction. An equivalent fluid density of 200�pef should be used for pessive rosistnnce desi�. These recommended valucs iocorporete safety factors of I.5 and 2.0 applied m the estimated ultimate values for frictional:snd passive rosistance,respectively. To achieve this value of passive taistance,the foundations slould be poured"neaP'a�ainst the native dense soils or compacted fill should be used as baek�ll egelost the froat of the footing, end the soil in front of the wall should extend a horizontal distence equal to at least three times the foundation depth. We recoinmend that dte upper l foot of soil be neglec.ted when calculating the passive rosistance. All wall backfill should be well compacted. Care should be teken to prcveat the buildup of excess laternl soil pressures, due to ovetcompaction of the wall backfill. This Catt be aeeonnplished by placing well backtill in&inch loose lifts and compaeting wlth small,hand•operated compactors. Permanent drsinagc systems should be installed for retainiag walls. We recommend t6at thase drainage sy�tema consist of an 18-inch-wide zotte of clean (less then 3 percent Fines), freo-dtainiag, granular mnterial placed along the back of the wall. Pea gravel is an acceptable drain mete�ial. Tlte grAnuler NELSON-COWRETTE&ASSOClATES, 1NC. 9�