2514 RAINIER AVE Geotech Report 2022-10-25

amec foster wheeler geotextile separator should be placed between the lacustrine silt (native soils) and the gravel bearing I pad. Spread footings constructed on gravel bearing pads may be designed for an allowable static bearing pressure of 2,500 pounds per square foot (psf). 111 Floors: Slab-on-grade floors should be designed to include an 8-inch subbase layer of gravel borrow, a 4-inch layer of washed crushed rock as a capillary break, and a vapor barrier placed on top of the capillary break layer. During wet weather work, a geotextile separator should be placed between the lacustrine silt and gravel subbase. 111 Stormwater Infiltration: While the Advance Outwash appears to have moderately high infiltration rates, infiltration would be negligible in areas with fill, lacustrine silt, topsoil, or any organic-rich soils. We I recommend in situ testing at specific locations and depths where stormwater infiltration would be desired to estimate long-term design infiltration rates. Observation wells should be installed at specific locations of proposed infiltration facilities to measure seasonally high groundwater levels. On-site Soil Considerations: The fill and native lacustrine silt soils will be very difficult to reuse as I structural fill except under ideal moisture and weather conditions. The fill encountered in the athletic field had a high fines and organics (topsoil) content and is therefore not suitable for reuse as structural fill. The contractor should take precaution to protect any exposed subgrades. Ideally, earthwork would be scheduled for the summer and fall months when drier weather occurs. I I I I i I Amec Foster Wheeler jj Project No.6-917-18116-0 \\Sea-fsl\WordProc\ Projects\18000s\1 8116 Everett School District\Geotech Report\Revised\2017_10-19_Everett Middle School Geotech_Sx.docx