1001 39TH ST 2016-01-01 MF Import

DAVID L. NELSON AND ASSOCIATES, INC. Consulting Engineering Gcology November 27; 1991 Project No. 10591 Page 10 II behind the wall. For planning purposes, :`ixed o.r r.on-yielding walls, we recommend that the "at rest" c;ondition should be assumed, and that an equivalent fluid pressure of 50 pounds per cubic foot (pcf) be used foz design pur��oses. For yielding walls, such as cantilever walls, the "a^tive" condition should be assumed and an equivalent fluid pressure� of 35 pcf be used. To develop the "active" pressure condi':ioa, the wall must be allowed to yield about its base a distance of ahout 0 . 001 times its total height. The effect of surcharges, such as traffic or floor loads, should also be considered. For a uniformly distributed load behind the wall, a corresYonding uniformly di:;tributed pressure equal to 30 percent or 50 percent of the surcharge should be added to the , lsteral soil pressure for yielding and non-yielding walls, res�ectively. if filling behind the� wall is performed, compaction of backfill within one-half of the wall embedment height beh5.nd the wall should be performed with light equipment, such that the wall is not adversely stressed. For planning purposes, design for lateral earth pressures acting on foundation walls could be resisted in the native glacial bearing soils by the use of a combination of foundation base friction and passive pressure. A �ase friction coefficien� of 0 . 40 is considered appropriate within the glacial deposits and Whidbey Formation. :. passive equivalent fluid pressure of 250 pcf should be used fo:: the on site soils. Where walls are located near slopes, the ground surface in front of the wall should be level for a distance of at least 3 times the depth of burial of the footing, to allow the above passive pressures. Otherwise, a reduction of passive pressure will be required. Specific reductions in passive pressure could be developed once the downslope geometry and bu�lding designs are known. An appropriate factor of safety should be applied to the above base iriction value to resist sliding. The above values assume the presence of the soils encountered in our explorations, and a free-draining mat�-.ria1 behind the subgrade wall. These values do not take into account hydrostatic pressures, sloping ground behind the wall, or surcharges due to equipment or adjacent structural loads . These values further assume the use of an effective drain system along the backside of the wall. We suggest the use of a free-draining sand and fine gravel backfill along the backside of the wall to reduce pressures on walls and to reduce potential for moisture problems. We suggest any basement or retaining wall areas utilize the recommendations as shown on the enclosed Subdrain & Backfill Scheme enclosed. The drainage blanket should extend to within about two ( 2 ) feet of fi>>ished exterior grade and have a minimum I�