1343 MADRONA AVE Geotech Report 2022-10-25

Geotechnical Engineering Report Stark Residence Addition 1343 Madrona Avenue Everett, Washington December 8, 2014 RN File No. 2902-001A Page 2 Geology Most of the Puget Sound Region was affected by past intrusion of continental glaciation. The last period of glaciation, the Vashon Stade of the Fraser Glaciation, ended approximately 14,000 years ago. Many of the geomorphic features seen today are a result of scouring and overriding by glacial ice. During the Vashon Stade, areas of the Puget Sound region were overridden by over 3,000 feet of ice. Soil layers overridden by the ice sheet were compacted to a much greater extent than those that were not. Part of a typical glacial sequence within the area of the site includes the following soil deposits from newest to oldest: Artificial Fill (af)-Fill material is often locally placed by human activities, consistency will depend on the source of the fill. The thickness and expanse of this material will be dependent on the extent of fill required to grade land to the desired elevations. Density of the fill will depend on earthwork activities and compaction efforts made during the placement of the material. Recessional Outwash (Qvr) -These deposits were derived from the stagnating and receding Vashon glacier and consist mostly of stratified sand and gravel, but include unstratified ablation and melt-out deposits. Recessional deposits were not compacted by the glacier and are typically not as dense as those that were. Vashon Till (Qvt)-The till is a non-sorted mixture of clay, sand, pebbles, cobbles and boulders, all in variable amounts. The till was deposited directly by the ice as it advanced over and eroded irregular surfaces of previously deposited formations and sediments. The till was well compacted by the advancing glacier and exhibits high strength and stability. Drainage is considered very poor in the till. Advance Outwash (Ova)-The advance outwash typically is a thick section of mostly clean, pebbly sand with increasing amounts of gravel higher in the section. The advance outwash was placed by the advancing glaciers and was overridden and well compacted by the glacier. Transitional Beds (Fraser Glaciation to Pre-Fraser Glaciation) (Qtb) --These deposits consist of clay, silt, and very fine to fine sand; some layers of peaty sand and gravel are in the lower part of compact but may be unstable because of high moisture content, plasticity, and local vertical jointing. The sediments were mostly deposited in still to slowly moving water, except for the coarse stream deposits in the lower part of the unit. The geologic units for this area are mapped on the Geologic Map of the Everett Quadrangle, Snohomish County, Washington, by James P. Minard (U.S. Geological Survey, 1985). The site is mapped as being underlain by transitional bed deposits. Our site explorations encountered transitional beds and outwash. Robinson Noble, Inc