801 E CASINO RD Geotech Report 2022-10-25

Cascade High School Subsurface Exploration and Synthetic Turf Field Geotechnical Engineering Report Everett, Washington Project and Site Conditions density of granular soils or the relative consistency of cohesive soils; these values are plotted on the attached exploration boring logs. The samples obtained from the split -barrel sampler were classified in the field and representative portions placed in watertight containers. The samples were then transported to our laboratory for further visual classification and laboratory testing, as necessary. 4.0 SUBSURFACE CONDITIONS Subsurface conditions on the project site were inferred from the field explorations conducted for this study, visual reconnaissance of the site, and a review of selected applicable geologic literature. As shown on the field logs, our exploration borings encountered up to 9 feet of fill overlying native materials consisting of dense to very dense silty sand with gravel interpreted as lodgement till sediments. 4.1 Stratigraphy Grass and Topsoil Each of the borings in the field encountered natural turf approximately 2 to 4 inches thick above a sand base approximately 6 inches thick. Fill Three of the exploration borings (EB-2, EB-3, and EB-4) encountered existing fill that was observed to be up to approximately 9 feet thick. The existing fill was typically very loose to dense silty sand with gravel and included variable organic content. Organic content analyses were completed on three selected soil samples retrieved from our exploration boring EB-4, and test results are included in the Appendix. For context in reviewing laboratory organic -content analyses, typical native topsoil generally has an organic content of about 2.5 to 4.5 percent expressed as a dry weight percentage. The upper 2.5 feet of the existing fill material was observed to contain significant organic content and is not recommended for use in compacted fill applications below the new field or other settlement —sensitive structures due to long-term settlement risk. The existing fill below 5 feet contained significantly less organic material, as shown on the laboratory test results included in the Appendix. Soil with significant organic content also tends to be somewhat elastic, yielding and rebounding under temporary loads. A primary objective when preparing synthetic turf subgrades is establishing a firm and unyielding surface that is precisely graded, which is difficult to attain when working with organic soils. The "Site Preparation" section of this report presents our recommendations for addressing existing fill soils below the new synthetic turf. March 20, 2017 ASSOCIATED EARTH SCIENCES, INC. DDV/Pt-1700BIE001-2—Projectsj201700811KEIM Page 3