5109 SOUND AVE 2017-08-02 - Laserfiche WebLink

July 21, 2014 Twa Single-Family residences L&A Job No. 14-065 Page 13 Concrete Retaining Wall A conventional reinforced concrete retaining wall, if used to stabilize the hillside in the southeast quadrant of the project site, should be founded on or into the Whidbey formation hard clayey silt soil. The retaining wall should be designed for static and seismic loading conditions. For static loading we recoinmend the wall be designed for an active soil pressure of 35 pcf EFD (equivalent fluid density) plus 0.75�i pcf, where (3 is the angle above horizon in degrees of the hillside behind the wall. The active soil pressure may be countered by a passive soil pressure of 400 pcf EFD for the portion of the wall extending below the hard clayey silt deposit. The above soil pressures are unfactored ultimate values. The retaining wall should be designed for a factor of safety of at least 1.5 against sliding and overturning failures and 2.5 against soil bearing failure under static loading. Footing foundations constructed on or into hard clayey silt deposit may be used to support the wall and an allowable soil bearing pressure of 4,OOU psf may be used for the design of the wal] footing foundations. "I'he Puget Sound region is in an active seismic zone. The reinforced concrete retaining wall should also be designed for an 100-year seismic event. We recommend a pseudo static loading be used for seismic loading design of the ��all. The active soil pressure should be an invert triangular distribution pressure diagram, with the magnitude of pressure at the top to be lOH[(35H+0.'75 (3)/35H] EFD, where (3 is the angle above horizon in degrees of the hillside behind the wall, and H the height of the wall from top to bottom of footing. The allowable stresses of the wall elements and the allowable soil bearing pressure may be increased by one third for design of short-duration seisinic LIU & ASSOCIATES, INC.