2320 RAILWAY AVE Geotech Report 2023-02-01

Interwest Construction Co. -Everett Contractor Yard Site Improvements, Everett,WA March 12,2021 Geotechnical Engineering Report P2184-T20 I We recommend that a representative from our firm be present during backfilling. Our representative will evaluate the adequacy of the subgrade soils and identify any areas needing further work, perform in-place moisture-density tests to determine if the work is being done in compliance with the compaction specifications and the intent of our recommendations,and advise on any modifications to procedure which might be appropriate for the prevailing conditions. 4_3 Spread Footings In our opinion,conventional spread footings will provide adequate support for the proposed scale house building if the subgrades are properly prepared. We offer the following comments and recommendations for spread footing design. Footing Depths and Widths: For frost and erosion protection, the bases of all exterior footings should bear at least 18 inches below adjacent outside grades,whereas the bases of interior footings need bear only 12 inches below the surrounding slab surface level. To reduce post-construction settlements, continuous (wall) and isolated (column) footings should be at least 18 and 24 inches wide, respectively. Bearing Subgrades: Footings should bear on medium dense or denser, undisturbed native soils which have been stripped of surficial organic soils and vigorously surface compacted, or on properly compacted structural fill which bears on the soils just described. We anticipate that adequate bearing soils will be encountered within 2 feet of existing grade across much of the project area, with existing fill materials being in a suitable enough condition to provide foundation support. In general,before footing concrete is placed, any localized zones of loose soils exposed across the footing subgrades should be compacted to a firm,unyielding condition,and any localized zones of soft, organic, or debris-laden soils should be overexcavated and replaced with suitable structural I I I I I I I fill. Lateral Overexcavations: Because foundation stresses are transferred outward as well as downward into the bearing soils, all structural fill placed under footings, should extend horizontally outward from the edge of each footing. This horizontal distance should be equal to the depth of placed fill. Therefore,placed fill that extends 24 inches below the footing base should also extend 24 inches outward from the footing edges. subgrade Observation: All footing subgrades should consist of firm,unyielding,native soils, the existing medium dense or denser gravelly fill,or structural fill materials that have been compacted to a density of at least 95 percent (based on ASTM:D-1557). Footings should never be cast atop loose,soft,or frozen soil,slough,debris,existing uncontrolled fill,or surfaces covered by standing water. Bearing Pressures: In our opinion,for static loading,footings that bear on dense properly prepared subgrades can be designed for a maximum allowable soil bearing pressure of 2,000 psf. A one-third increase in allowable soil bearing capacity may be used for short-term loads created by seismic or wind related activities. Migizi Group, Inc. Page 11 of 16 MIGRI Iiiiii i,