1228 GRAND AVE Geotech Report 2022-10-25

April 7,2008 Mr.Don Levin L&A Job No. 8A037 Page 12 be used for lateral resistance. The above passive pressure assumes that the backfill is level or inclines upward behind the foundations for a horizontal distance at least twice the depth of the foundations below final grade. A coefficient of friction of 0.60 between the foundations and the subgrade soils may be used. The above soil parameters are unfactored values,and a proper factor of safety should be used in calculating the resisting forces against lateral loads on the buildings. BASEMENT WALLS Basement walls of the proposed new residence would be restrained at the top from lateral movement and should be designed for a lateral soil pressure under the at-rest condition. We recommend that an at-rest soil pressure of 45 pcf EFD(equivalent fluid density)be used for the design of basement walls or extended footing walls. To counter the above active soil pressure, a passive lateral soil pressure of 350 pcf EFD may be used. To resist against sliding, the friction force between-the footings and the subgrade soils may be calculated based on a coefficient of friction of 0.60. The above soil parameters are ultimate values based on a fully drained condition of the walls, and proper factors of safety factors should be applied in the design of the basement walls or extended footing 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 or crushed rock, should be placed against the back of basement or extended footing walls to prevent accumulation of groundwater behind and buildup of hydrostatic pressure against the walls. This drainage blanket fill should be compacted to a non- yielding state with a vibratory compactor. Structural fill should be used for backfilling the walls behind the vertical drainage blanket. The top 12 to 18 inches of the backfill may consist of compacted, clean, on-site granular soils. In order not to damage the basement walls, only hand- held, light-weight, compaction equipment should be allowed within a horizontal distance of the LIU & ASSOCIATES, INC.