2320 RAILWAY AVE Geotech Report 2023-02-01

I I Interwest Construction Co.-Everett Contractor Yard Site Improvements, Everett,WA March 12,2021 Geotechnical Engineering Report P2184-T20 I I I I I 4.5 Truck-Scale Pits and Concrete Wet Pond The precast truck-scale pits and sediment collection and concrete stormwater wet pond will encounter poorly consolidated alluvial sands and peat underlying the upper yard fill. This material will cave and run during excavation, so temporary shoring will likely be required. Groundwater levels are expected to be near the bottom of the excavations,and seepage should be anticipated. We anticipate that an internal system of ditches, sump holes, and pumps will be adequate to temporarily dewater excavations that do not extend deeply into the water table. The truck-scale pits and sediment collection and concrete stormwater wet pond should be supported on 24 inches of 2 to 4-inch quarry spalls driven into the subgrade or according to the manufacturer's directions. The sump structures should be designed to resist active earth pressures of 35 pcf equivalent fluid for drained conditions and 80 pcf for undrained conditions.P 4.6 Asphalt Pavement Since a heavy-duty pavement curtain is proposed along the perimeter and southcentral portion of the site we offer the following comments and recommendations for pavement design and construction. ISubgrade Preparation: All soil subgrades should be thoroughly compacted,then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be over excavated to a minimum depth of 12 inches and replaced with a suitable structural fill material. All structural fill should be compacted according to our recommendations given in the Structural Fill section. Specifically, the upper 2 feet of soils underlying pavement section should be compacted to at least 95 percent(based on ASTM D-1557), and all soils below 2 feet should be compacted to at least 90 percent. I Pavement Materials: For the base course, we recommend using imported washed crushed rock, such as"Crushed Surfacing Base Course" per WSDOT Standard Specification 9-03.9(3)but with a fines content of less than 5 percent passing the No. 200 Sieve. For the subbase course, we recommend using imported, clean, well-graded sand and gravel such as "Ballast" or "Gravel Borrow" per WSDOT Standard Specifications 9-03.9(1) and 9-03.14, respectively. Conventional Asphalt Sections: A conventionalpavement section typicallycomprises an asphalt p P P I I concrete pavement over a crushed rock base course. We recommend using the following I conventional pavement section, or thicker if required by the City of Everett: Minimum Thickness I Pavement Course Heavy Duty Section Asphalt Concrete Pavement 4 inches Crushed Rock Base 8 inches Granular Fill Subbase 24 inches I I Migizi Group, Inc. Page 13 of 16 MIGIZI iiIili' II