5200 EVERGREEN WAY SEPA 017 - 010 Geotech Report 2025-04-23

Subsurface Exploration, Geologic Hazards, and Former Brien Ford Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations conditions. The native and existing fill soils present onsite contained significant amounts of silt and are considered highly moisture-sensitive. On-site soils may only be reused in structural fill applications if specifically allowed by project plans and specifications, and if moisture conditions can be achieved that allow compaction to a firm and unyielding condition and to the specified minimum density for the application where they are used. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction with at least 25 percent retained on the No. 4 sieve. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of in-place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses, and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing program. 11.0 FOUNDATION UNDERPINNING Existing foundations located adjacent to the proposed excavation for environmental remediation at the project site will require underpinning for support during removal of contaminated soils. We anticipate that the foundation for the wall that separates commercial sales from the service intake building as well as the north end of the foundation of the auto detail shop will require underpinning. The subsurface explorations completed for this study and preceding studies encountered areas of variable surficial fill soils, ice-contact deposits, or dense native advance outwash sediments. Underpinning elements (pipe piles) should fully penetrate the existing fill soils and ice-contact deposits and be supported by the underlying outwash sediments. 11.1 Pipe Piles A deep foundation system consisting of small-diameter driven pipe piles may be used for foundation support where existing foundations will be undermined by the proposed excavation. The pipe piles should consist of Schedule 40 steel pipe, driven to refusal, which is defined as less than a given amount of penetration during a time interval of continuous driving using a hydraulic hammer. The time interval of continuous driving and the allowable pile load is dependent upon the pipe pile diameter and the weight of the driving hammer (see Table 1). At the request of the project structural engineer, we have provided design recommendations for 3-inch-diameter and 4-inch-diameter piles in Table 1. The depth of pile embedment into the May 16, 2017 ASSOCIATED EARTH SCIENCES,INC. AWR/Id-160594V003-2-Projects1201605941KVIWP Page 11