1018 14TH ST 2023-02-09 - Laserfiche WebLink

SHANNON 6WILSON,INC. moisture content of each sample was determined to aid in estimating soil unit weight. Soil grain size determinations and fines content determinations were made on selected samples to aid in soil classification and to provide information needed for determining soil parameters and liquefaction potential. Two Atterberg Limits tests were perfonned to determine the plasticity of fine-grained materials. The results of the tests are presented in Appendix B and shown in the boring logs in Appendix A. 3.0 SUBSURFACE CONDITIONS 3.1 Regional Geologic Setting The project is located in the central portion of the Puget Lowland, an elongated. north-south depression situated between the Olympic Mountains and the Cascade Range. Repeated glacial advances (glacial events) into this region strongly influenced present-day topography, geology, and groundwater conditions in the project area. The ice for these glaciations originated in the Coast Range and Rocky Mountains of British Columbia, Canada, and generally advanced (flowed) southward into the Puget Lowland. Each glaciation deposited new sediment and partially eroded previous sediments. During the intervening periods when glacial ice was not present, normal stream processes, wave action, weathering, and landsliding eroded and reworked some of the glacially derived sediment, further complicating the geologic setting. During the most recent glaciation that covered the central Puget Lowland, approximately 18,000 to 13,000 years before present(Porter and Swanson, 1998), the glacial ice is estimated to have ranged from about 3,000 to 5,000 feet thick in the deepest part of the trough (Thorson, 1989). The weight of the glacial ice resulted in compaction (overconsolidation) of the glacial and nonglacial soils beneath the ice. As the last ice to reach the Puget Lowland (Vachon Stade of the Fraser Glaciation) retreated to the north, deposits of sand, gravel, silt, and clay, often containing cobbles and boulders, were laid down by meltwater streams issuing from the glacial ice front. These deposits are termed glacial recessional soils and are not glacially consolidated. The proposed bulkhead replacement site is located along the east shore of Possession Sound. Prior to construction of the original bulkhead and other Port facilities,the site was likely situated at the southern edge of the Snohomish River delta. The glacial and interglacial deposits in this area are overlain by younger(Holocene Epoch), relatively loose and soft, post-glacial soils that include beach, alluvial, estuarine, and fill deposits. 21-1-21761-003-R I f.docx4p/clp 21-1-21761-003 5