8407 BROADWAY SECURE SPACE STORAGE Geotech Report 2025-04-24

ZipperGeo Broadway Everett Expansion Project No. 2601.01 Geoprofessional Consultants July 7, 2022 structural fill and moisture conditioning will be impossible. If earthwork occurs during wet weather, the project team should assume that site soils will not be suitable for reuse as structural fill. It should also be noted that trace amounts of plastic and charcoal materials were identified in samples obtained at 5 and 7.5 feet bgs in boring B-3. Although the amount of this deleterious material observed in these samples does not appear to preclude their reuse as structural fill, higher amounts of deleterious materials could be encountered beneath the ground surface. The suitability of reusing site soils that contain deleterious materials should be made during construction by a representative from ZGA. Imported Structural Fill Imported structural fill may be required during earthwork.The appropriate type of imported structural fill will depend on the weather conditions. During extended periods of dry weather,we recommend imported fill meet the requirements of Common Borrow, Type 2 as specified in Section 9-03.14(3) of the 2020 WSDOT Standard Specifications. The on-site soils would be classified as Common Borrow, Type 2. During wet weather, higher-quality (lower fines content) structural fill might be required, as Common Borrow may contain sufficient fines to be moisture sensitive. During wet weather, we recommend that imported structural fill meet the requirements of Gravel Borrow as specified in Section 9-03.14(1) of the Standard Specifications. Moisture Content The suitability of soil for use as structural fill will depend on the prevailing weather at the time of construction,the moisture content of the soil, and the fines content(that portion passing the US No. 200 sieve)of the soil.As the amount of fines increases,the soil becomes increasingly sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (such as most of the on-site soils) cannot be consistently compacted to the appropriate levels when the moisture content is more than approximately 2 percent above or below the optimum moisture content (per ASTM D1557). Optimum moisture content is that moisture content which results in the greatest compacted dry density with a specified compactive effort. Fill Placement Structural fill should be placed in horizontal lifts not exceeding 10 inches in loose thickness. Each lift of fill should be compacted using compaction equipment suitable for the soil type and lift thickness. Each lift of fill should be compacted to the minimum levels recommended below based on the maximum laboratory dry density as determined by the ASTM D1557 Modified Proctor Compaction Test. Moisture content of fill at the time of placement should be within plus or minus 2 percent of optimum moisture content for compaction as determined by the ASTM D1557 test method. Compaction Criteria Our recommendations for soil compaction are summarized in the following table. Structural fill for roadways and utility trenches in municipal rights-of-way should be placed and compacted in accordance with City of Everett codes and standards. We recommend that a geotechnical engineer be present during 8