7100 HARDESON RD Geotech Report 2025-03-06

Geotechnical Engineering Report lierracon Merrill Creek Operations Base Expansion • Everett, Washington December 14, 2020 • Terracon Project No. 81205012 GeoRepol't LIQUEFACTION Liquefaction is the phenomenon where saturated soils develop high pore water pressures during seismic shaking and lose their strength characteristics. This phenomenon generally occurs in areas of high seismicity, where groundwater is shallow and loose granular soils or relatively non- plastic fine-grained soils are present. Based on the site geology and subsurface groundwater conditions, the risk of widespread liquefaction of the site soils is low for this site during a design level earthquake. However,zones of medium dense soil beneath the groundwater table were encountered during exploration, and zones of isolated liquefaction may occur during a design level earthquake. Because the groundwater table is relatively deep, the effects of isolated liquefaction is likely to be muted, but may result in differential settlement beneath building foundations and floor slabs. The magnitude of these settlements has not been calculated but is expected to be minor. FLOOR SLABS Design parameters for floor slabs assume the requirements for Earthwork have been followed. Specific attention should be given to positive drainage away from the structure and. positive drainage of the aggregate base beneath the floor slab. Floor Slab Design Parameters Item Description Minimum 6 inches of free-draining (less than 5% passing the U.S. No. 200 Floor Slab Support sieve)crushed aggregate compacted to at least 95% of ASTM D 15572' 3 Estimated Modulus of Subgrade Reaction 2 100 pounds per square inch per inch (psi/in)for point loads 1 Floor slabs should be structurally independent of building footings or walls to reduce the possibility of floor slab cracking caused by differential movements between the slab and foundation. 2 Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade condition, the requirements noted in Earthwork, and the floor slab support as noted in this table. It is provided for point loads. For large area loads the modulus of subgrade reaction would be lower. 3 Free-draining granular material should have less than 5%fines(material passing the No. 200 sieve). Other design considerations such as cold temperatures and condensation development could warrant more extensive design provisions. The use of a vapor retarder should be considered beneath concrete slabs on grade covered with wood, tile, carpet, or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder. I Responsive • Resourceful • Reliable 14