4920 24TH AVE W Geotech Report 2023-06-22

GeoTest Services, Inc. October 8, 2021 2405 Hillside Lane, Everett,WA Project No.21-0845 mom fill placed over firm and unyielding native subgrade.The exposed subgrade should be viewed by the Geotechnical Engineer and 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, compacted, 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, provide a capillary break,and act as a drainage layer.To help reduce the potential for water vapor migration through floor slabs,a continuous 10-mil minimum thick polyethylene sheet with tape-sealed joints should be installed below the slab to serve as an impermeable vapor barrier. The vapor barrier should be installed and sealed in accordance with the manufacturer's instructions. Foundation and Site Drainage Positive surface gradients should be provided to direct surface water away from developed areas and toward suitable drainage facilities. Roof drainage from residential construction 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 the building 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 building foundations as shown in the Typical 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 within approximately 1 foot of the finished grade and consist of open-graded drain rock containing less than 3 percent fines by weight 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 invert of the footing drainpipe should be placed at approximately the same elevation as the bottom of the 13