1515 132ND ST SE Geotech Report 2022-10-25

Proposal for Geotechnical Engineering Services Proposed Bank: 1515 132nd Street Southeast, Everett, Washington March 15, 2019 should consist of a well graded soil free of organic material with less than 5 percent fines (silt and clay sized particles passing the U.S. 200 sieve). Structural fill should be moisture conditioned to within about 3 percent of optimum moisture content, placed in loose, horizontal lifts less than 8 inches in thickness, and compacted to at least 95 percent maximum density, determined using ASTM D-1557 (Modified Proctor). The procedure to achieve proper density of a compacted fill depends on the size and type of compacting equipment, the number of passes, thickness of the lifts being compacted, and certain soil properties. If the excavation to be backfilled is constricted and limits the use of heavy equipment, smaller equipment can be used, but the lift thickness will need to be reduced to achieve the required relative compaction. Generally, loosely compacted soils are a result of poor construction technique or improper moisture content. Soils with high fines contents are particularly susceptible to becoming too wet and coarse -grained materials easily become too dry, for proper compaction. Silty or clayey soils with a moisture content too high for adequate compaction should be dried as necessary, or moisture conditioned by mixing with drier materials, or other methods. 6.4.1 Underground Storage Tank Decommissioning Backfill As part of the planned improvements the underground storage tanks located to the south of the existing fueling station island will be decommissioned and the excavation backfilled. The excavation backfill should consist of structural fill. Due to the presence of increased moisture and saturated soils encountered in our borings at 7 to l l %2 feet below grade, there is a potential for groundwater seepage to be encountered in the tank excavation. If fill will need to be placed into standing water, the fill should consist of 2- to 4-inch quarry spalls meeting the requirements of WSDOT 9-13.1(5) (WSDOT, 2018). The spalls should be locked into place using the bucket of an excavator. Above the standing water, a granular structural fill may be used. In order to prevent the migration of the granular fill into the quarry spalls, a layer of non -woven filter fabric, such Mirafi 140N, or approve equivalent should be used at the transition between fill materials. 6.5 WET WEATHER CONSTRUCTION The wet season in Western Washington typically extends from October through May. Earthwork during the wet season requires planning and may require the use of imported wet weather fill materials that can increase earthwork costs. General recommendations 19-049 1515 132nd St SE Page 12 PanGEO, Inc.