4320 THOMSON AVE GEOTECHNICAL ENGINEERING REPORT Geotech Report 2023-08-10

GeoTest Services, Inc. 4320 Thomson Avenue, Everett, WA Floor Support March 17, 2022 Project No. 22-0285 Floor slabs may be supported on properly prepared, firm and unyielding native subgrade or on properly placed and compacted structural fill placed over properly prepared native soil. Prior to placement of the structural fill, properly prepared subgrade soil should be proof -rolled as recommended in the Site Preparation and Earthwork section of this report. GeoTest recommends that interior concrete slab -on -grade floors be underlain with at least 6 inches of clean, crushed, free -draining gravel. The gravel should contain less than 3 percent passing the U.S. Standard No. 200 sieve (based on a wet sieve analysis of that portion passing the U.S. Standard No. 4 sieve). The purpose of this gravel layer is to provide uniform support for the slab and act as a drainage layer. Exterior concrete slabs -on -grade, such as sidewalks, may be supported directly on undisturbed native soil or on properly placed and compacted structural fill; however, long-term performance will be enhanced if exterior slabs are placed on a layer of clean, durable, well -draining granular material. Foundation and Site Drainage Positive surface gradients should be provided adjacent to new foundation areas to direct surface water away from the building and toward suitable drainage facilities. Roof drainage should not be introduced into the perimeter footing drains but should be separately discharged directly to the stormwater collection system or similar municipality -approved outlet. Pavement and sidewalk areas, if present, should be sloped and drainage gradients should be maintained to carry surface water away from foundation areas towards an approved stormwater collection system. Surface water should not be allowed to pond and soak into the ground surface near buildings or paved areas during or after construction. Construction excavations should be sloped to drain to sumps where water from seepage, rainfall, and runoff can be collected and pumped to a suitable discharge facility. To reduce the potential for groundwater and surface water to seep into interior spaces, GeoTest recommends that an exterior footing drain system be constructed around the perimeter of new foundations as shown in the Conceptual Footing and Wall Drain Section (Figure 3) of this report. The drain should consist of a perforated pipe measuring 4 inches in diameter at minimum, surrounded by at least 12 inches of filtering media. The pipe should be sloped to carry water to an approved collection system. The filtering media may consist of open -graded drain rock wrapped in a nonwoven geotextile fabric such as Mirafi° 140N (or equivalent) or wrapped with a graded sand and gravel filter. For foundations supporting retaining walls, drainage backfill should be carried up the back of the wall and be at least 12 inches wide. The drainage backfill should extend from the foundation drain to 7