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October 3, 2016 Single-Family Residence L&A Job No. 16-124 Page 16 CAST-IN-PLACE CONCRETE WALLS Building foundation walls, if required to retain soils, should be designed as retaining walls. Foundation walls restrained at the top from lateral movement are considered unyielding and should be designed for a lateral soil pressure under the at-rest condition. Retaining walls unrestrained at the top from lateral movement may be designed for active soil pressure. We recommend that an at-rest soil pressure of 55 pcf EFD(equivalent fluid density) and an active soil pressure of 35 pcf EFD be used for the design of building foundation walls and retaining walls, respectively, with a level or descending backslope away from the walls. For walls with ascending backslope away from the walls, an additional pressure of 0.75 pcf per degree of the backslope angle above the horizontal should be added to the above design pressures. To counter the above active or at-rest pressure, a passive lateral soil pressure of 300 pcf EFD may be used. This passive pressure value is applicable only to walls with a level or ascending backslope away from the walls for a horizontal distance of at least 1.5 times the wall height To resist against sliding,the friction force between footings and subgrade soils may be calculated based on a coefficient of friction of 0.55 (ultimate value). The above soil parameters are ultimate values based on a fully drained condition of the walls, and proper factors of safety should be applied in the design of the building basement walls and retaining walls against sliding and overturning failures. A vertical drainage blanket, at least 12-inch-thick horizontally, consisting of clean, free- draining,pea gravel or washed gravel should be placed against the back of foundation and retaining walls to within 18 inches of the finish grade to prevent accumulation of groundwater behind and buildup of hydrostatic pressure against the walls. This drainage LIU & ASSOCIATES, INC. 211 3 3