2908 49TH ST SW 2016-01-01 MF Import

September 7, 2010 Mr. John Mustach L&A Job No. 10-036 Page 4 any, within thc keyway trench of the wall should be over-excavated down to dense Esperance Sand soil and backfilled with stcuciural fill. A vertical drainage blanket should be placed against the back of the blocks and should be hydraulically connected to the wall drain line. Structural iill should be uscd to backfill the wall behind the vertical drainage blanket. Dcsign Soil Parametcrs The proposed prccast conerete block wall varies from less than 4 fect to about ] 0.5 feet ta(I. We recommcnd that the wall be designed for a fully drained wndition in accordance with thc following soil perimcters: Unit Wcight, 7', pcf Angle of Internal Friction, �, dcgrecs Cohesion, c, psf Reinforccd Retained SOIIS SOIIS 135 125 3C 34 0 0 Poundation Levcling Soils Rock Base 135 135 36 40 0 0 "I'hc block wall should bc designcd for a iuinimum lactor of 1.5 against sliding failurc, 1.7 against overturning fuilurc and 2A against foundation bcaring failure under the static loading condition. 7'he Puget Sound region is in an aclive seismic zone snd the block wal( should also be designed undcr thc scismic loading condition for a 100-year seismic evenL The peak ground acceleration 1'or such a�� event in the Puget Sound region is about 03g (g = gravity force). The block wall, howcvcr, arc built with intcrlocking wncrcte blocks with somc (lexibility, and ihe block do not movc in unison during carihquakes. Thcrclorc, for design of thc block wall under the seismic loading condition, the ground acceleration may be reduced to 0.2g. The block wall should designed for a factor of safety o1� at least l.l against sliding failure, 1.15 against overturning 1'ailure and 1.5 against foundation bearing failure under [he seismic loading condition. LIU & ASSOCIATES, INC.