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Geotechnical Engineering Report <br /> Proposed New Storm Water Vault <br /> Northwest Mitsubishi <br /> November 18, 2002 <br /> CG File No. 1397 <br /> Page 7 <br /> the wall are in an "active"condition. Walls restrained from movement by stiffness or bracing are <br /> in an "at-resP' condition. Active earth pressure and at-rest earth pressure can be calculated based <br /> on eyuivalent fluid densiry. 'I'he recommended values fur the drained and undrained condition in <br /> both the active and at-rest cases are preseuted in the table below. <br /> Lateral loads can be resisted by friction betwecn the foundation and subgrade soil, ar.d by passive <br /> soil resistance acting on the below-grade portion of the foundation. For the latter, G�e foundation <br /> must be pourcd "neat" against undisturbed soil or backfilled with clean, free-draining, compacted <br /> structural fill. Passive resistance may be calculatcd as a triangular equivalent tluid pressure <br /> distribution. The upper 1-foot of soil should be ignored whcn calculating the passivr_ resistance <br /> unless covered with a hard surface like asphalt or concrete. <br /> Backfill t c Active ressure At-rest ressure Passive ressure <br /> <90% AS'IT1 D 1557 45 pcf drained GS pcf drained 180 pcf <br /> 85 cfundrained 95 efundrained <br /> 90%+ P�S7'M D 1557 35 pcf drained 55 pcf drained 220 pcf <br /> 80 cfimdraincd 90 cfundrained <br /> We recommcnd an allowablc cucfficient of friction betwcen the footings and be�ring soil of 0.44 <br /> be used in design providcd that the foundation is placed as recommended in this report. This <br /> figure should be applicd to thc vcrtical dcad load only. <br /> Surcharge effccts shou'd Uc considcred whcrc appropriatc. Increased lateral earth pressure due to <br /> adjacent vertical surchargc pressures may be calculated as a unifom� pmssure distribu�ion equ�'. <br /> to 0.4� times the vcrtical surcharge pressure for at-rest conditions, and 03 times the vertical <br /> surcharge pressure for acti��e condidons. Por esample, if 200 pound per square foot area <br /> surcharge is used for adjacent parking areas, then in the at-rest condition, a imiforni pressere <br /> dstnbution of 90 pounds per square foot should be applied against ihe retaining wall. <br /> Thc abo��c ��alucs include a factor of safcty of 2.0 applicd to our estimate of thc ultimate value of <br /> passi��c pressurc in ordcr to limit latcral moecmcnt. <br /> Cornerstone Geotechnical, Inc. �\ <br /> �J <br />