223 PECKS DR 2016-01-01 MF Import

�, �--± RPtai_nina Walls Static design of basement walls str.ucturally braced against movement should be based on an equivalent fluid density of 50 pcf. This pressure assumes that the backfill is imported free draining granular mate.�ial with a horizontal surface and that there is no water pressure behind the wall. Uniform lateral pressures due to a uniform vertical surcharge behind a braced wall should be computed using a coefficient of 0 . 95 times the ' uniform vertical surcharge load. Care should be exercised in compacting backfill against retaining walls. Heavy equipment should not approach retaining walls close enough to intrude within a 1 : 1 line drawn upward from the bottom of the wall. Backfill close to walls should be placed and compacted with hand-operated equipment. All fill and backfill should be compacted to at least 90 percent of the maximum dry density as determined by the ASTM D1557 test method. Design wall pressures given above assume no water pressure behind the walls. We recommend that an adequate drain system be provided at the base of all retaining walls. As a minimum, wall drains should consist of a four-inch diameter perforated PVC drain pipe placed in at least one cubic foot of drain gravel per lineal foot along the base of the wall. Drain gravel should meet the gradation requirements of the Washington State DOT Standard Specifications Section 9-03. 12 (4) . Imported granular fill used for backfill of retaining walls should be capped with paving or 12 in^,hes of onsite silty soils to reduce surface water infiltration. Asphalt emulsion or other appropriate damp- proofing should be applied to the basement wall as a minimum. Conventional spread footing foundations founded on undisturbed natural glacial bearing soils (as defined in this report) may be used for support of retaining walls. Design of walls and their foundations should be performed by a qualified structural engineer in accordance with the recommendations presented in this report.