9205 4TH AVE W 2025-12-03 - Laserfiche WebLink

July 2, 2008 Duplex Buildings L&A Job No. 8AO67 Page 4 The Vashon till soil unit is normally underlain by an Advance Outwash soil unit composed of stratified sand and gravel with minor amounts of silt and clay, deposited by the meltwater of advancing glacial ice. Due to their generally granular composition, the advance outwash deposits are of moderate permeability and drains fairly well except in the more silty zones of this soil unit. The advance outwash deposits are glacially overridden and are generally dense to very dense in its natural, undisturbed state, except the top 2 to 4 feet where exposed on slopes which may be weathered to a loose to medium -dense state. The advance outwash deposits can stand in steep cuts or natural slopes for extended period when undisturbed. Where exposed on slopes with poor vegetation cover and subject to storm runoff or groundwater seepage, the advance outwash deposits can be gradually eroded and may slough and redeposit to a flatter inclination. The underlying fresh advance outwash deposits in their native, undisturbed state can provide good foundation support with little settlement expected for light to moderate residential structures. SOIL CONDITIONS The subsurface conditions of the site were explored with four test pits. These test pits were excavated on June 16, 2008, with a rubber -tired backhoe to depths from 6.0 to 6.5 feet. The approximate locations of the test pits are shown on Plate 2 - Site and Exploration Location Plan. The test pits were located with either a tape measure or by visual reference to existing topographic features in the field and on the topographic survey map, and their locations should be considered only accurate to the measuring method used. A geotechnical engineer from our office was present during subsurface exploration, who examined the soil and geologic conditions encountered and completed logs of test pits. Soil samples obtained from each soil unit in the test pits were visually classified in general accordance with United Soil Classification System, a copy of which is presented on Plate 3. LIU & ASSOCIATES, INC.