12728 19TH AVE SE BASE FILE Geotech Report 2025-07-29

I May 28, 2007 Proposed Office Building L&A Job No. 7A053 Page 4 underlying fresh till is very dense and is practically impervious to stormwater infiltration. The fresh till has the strength of low-grade concrete and can stand in a steep natural or cut slope for a long period. If remains undisturbed and well-drained, the fresh till can provide excellent foundation support with little settlement expected. 1 SOIL CONDITIONS Subsurface conditions of the site were explored with five test pits spread throughout the site. The test pits were excavated on May 3, 2007, with a track-mounted backhoe to depths from 4.5 111 to 5.0 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 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. Detailed descriptions of soils encountered during site exploration are presented in test pit logs on Plates 4 through 6. The test pits encountered a layer of loose, organic topsoil, from 10 to 14 inches thick, mantling the site. The topsoil is underlain by a layer of weathered soils of brown,medium-dense, silty fine sand with a trace of gravel, from about 1.5 to 2.0 feet thick. Underlying this layer of weathered soils to the depths explored is a light-gray fresh Vashon till deposit of very-dense, weakly- cemented,gravelly,silty,fine sand,with occasional cobble. P LIU & ASSOCIATES, INC. P