801 E CASINO RD Geotech Report 2022-10-25

Cascade High School Subsurface Exploration and Synthetic Turf Field Geotechnical Engineering Report Everett, Washington Design Recommendations Project planning and construction should follow local standards of practice with respect to TESC. Best management practices (BMPs) should include but not be limited to: • Provide storm drain inlet protection; • Route surface water away from work areas; • Keep staging areas and travel areas clean and free of track -out; • Cover work areas and stockpiled soils when not in use; • Complete earthwork during dry weather and site conditions, if possible. 7.0 SITE PREPARATION We understand that new site grades will be similar to existing site grades with cuts and fills expected to be on the order of 2 feet or less. Site preparation for the renovated field should include removal of the existing sod and topsoil and re -grading to establish design subgrade elevation in preparation for the installation of the new field components. Once stripping, demolition, and excavation to subgrade elevation have been completed, the resulting subgrade should be assessed. We anticipate that the exposed soils will consist of native silty sand and existing fill. The subgrade should be compacted to 90 percent of the modified Proctor maximum dry density as determined by American Society for Testing and Materials (ASTM) D-1557. Any soft, yielding, or excessively organic areas should be overexcavated to expose suitable bearing soils and planned grade restored with compacted structural fill. Based on our subsurface explorations, the uppermost 2 to 3 feet of existing fill is typically highly organic and loose and will likely require removal. Below 2.5 feet, existing fill was typically less organic and dense and can likely be left in place. Native soils and existing fill soils deeper than 2 to 3 feet were observed to be very silty and are therefore very moisture - sensitive. We anticipate that site soils will be most economical to work during the summer when soil moisture content can be adjusted by aeration and drying. Controlling soil moisture by aeration is not expected to be feasible during wet site and weather conditions. This site is a good candidate for soil cement treatment if wet surface soils are encountered at the time of construction. We recommend that soil cement treatment be included in the base bid if the project will be constructed in the winter. The on -site soils contain a significant amount of fine-grained material, which makes them moisture -sensitive and subject to disturbance when wet. The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. It should be noted that the moisture content of the site soils was visually estimated to be above the optimum moisture content for compaction purposes at the time of March 20, 2017 ASSOCIATED EARTH SCIENCES, INC. DDV/pc-170081EOOI-2-ProjedsJ20170081JKEJWP Page 6