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N <br /> ' DAV�D L. NELSON AND ASSOCIATES, INC. <br /> �.� Consulting Enginccring Gaology <br /> k� May 31 , 1991 <br /> Project No. 4791 <br /> Page 10 <br /> Ii <br /> � such as cantilever walls, the "active" condition may be assumed and an <br /> �' equivalent fluid pressure of 35 pcf be used. To develop the "active" pressure <br /> i condition, the wall must be allowed to yield about its base a distance of <br /> about 0.007 times its total height. <br /> {i <br /> ' The effect of surcharges, such as traffic or floor loads, should also be <br /> � " considered. For a uniformly distributed load behind the wall, a corresponding <br /> � uniformly distributed pressure equal to 30 percent or 50 percent of the <br /> I� surcharge should be added to the lateral soil pressure for yielding and non- <br /> � ieldin walls res <br /> y g , pectively. If filling behind the wall is performed, <br /> � p compaction of backfill within one-half of the wall embedment height behind the <br /> I wall should be performed with light equipment such that the wall is not <br /> adversely stressed. <br /> f : <br /> � <br /> For planning purposes, design for lateral earth pressures acting on foundation <br /> � ' walls could be resisted in the native glacial bearing soils by use of a <br /> � combination of foundation base friction and passive pressure. A base friction <br /> i coefficient of 0.45 is recommended within the dense glacial till. A passive <br /> � '' equivalent fluid pressure of 450 pcf is recommended within the dense qlacial <br /> � till. Where walls are located near slopes, the ground surface in front of the <br /> � , wall should be level for a distance of at least 3 times the depth of burial of <br /> the footing, to allow the above passive pressures. Otherwise, a reduction of <br /> i <br /> � � passive pressure will be required. Specific reductions in passive pressure <br /> could be developed once the downslope geometry and building designs are known. <br /> ' An appropriate factor of safety should be applied to the above base friction <br /> 1 ! <br /> value to resist sliding. <br /> � � The above values assume the presence of the soils encountered in our <br /> � explorations, and a free-draining material behind the subgrade wall. These <br /> � q values do not take into account hydrostatic pressures, slopinq ground behind <br /> the wall, or surcharges due to equipment or adjacent structural loads. These <br />