6202 ASSOCIATED BLVD Geotech Report 2022-10-25

Proposed Everett Warehouse Project No. 2152.01 March 5, 2019 site are expected to consist of sands with a significant fines content (15 to over 30 percent). 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 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. Laboratory testing of select soil samples indicates the in -place moisture content of site soils ranges from about 7 to 19 percent with an average of about 10.4 percent. Optimum moisture content of site soils is estimated at about 8 percent. Therefore, site soils appear somewhat above optimum moisture content for compaction. Site soils will only be suitable for reuse as structural fill during dry weather. During wet weather, site soil will quickly become too wet for reuse as structural fill. During wet weather, the project team and bidding contractors should expect that site soils will not be suitable for reuse as structural fill and imported fill with little to no fines content will be required. We recommend that site soils used as structural fill have less than 4 percent organics by weight and have no woody debris greater than % inch in diameter. We recommend that all pieces of organic material greater than % inch in diameter be picked out of the fill before it is compacted. Any organic -rich soil derived from earthwork activities should be utilized in landscape areas or wasted off site. Imported Structural Fill: If earthwork occurs during wet weather, imported structural fill may be required. The appropriate type of imported structural fill will depend on weather conditions. During extended periods of dry weather, we recommend imported fill, at a minimum, meet the requirements of Common Borrow as specified in Section 9-03.14(3) of the most current version of the Washington State Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard Specifications). During wet weather, higher -quality 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 WSDOT Standard Specifications. Prior to importing structural fill for general use in raising site grades, we recommend we be provided a sample of the material to evaluate its suitability for use as structural fill. Retaining Wall Backfill: Cast -in -place concrete foundation retaining walls should include a drainage fill zone extending at least 2 feet back from the back face of wall for the entire wall height. The drainage fill should meet the requirements of Gravel Backfill for Walls as specified in Section 9-03.12(2) of the WSDOT Standard Specifications. 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 the jurisdiction codes and standards. We recommend that a geotechnical engineer be Page 8