10200 19TH AVE SE COSTCO FUEL STATION Geotech Report 2022-10-25

mpEOTECHNICAL ENGINEERING STUDY ostco Wholesale c/o Barghausen Consulting Engineers E-8556 January 13, 1999 Page 5 The existing fill and native soils are moisture sensitive, and will become unstable when exposed to- excessive moisture. Compaction and grading of these soils will be difficult if the moisture content is above optimum. During dry weather, the existing silty sand soils can be considered for use as structural fill, provided the moisture content of the soil is at or near optimum at the time of placement. At the time of our exploration, the existing fill and native silty sand soils were generally above the optimum moisture content, and would require moisture conditioning before placement. Fill for use during wet weather should consist of a fairly well graded granular material having a maximum size of three inches and no more than five percent fines passing the No. 200 sieve based on the minus 3/4-inch fraction. Structural fill is defined as compacted fill placed under foundations, roadways, slabs, pavements, or other load-bearing areas. Structural fill under slabs and footings should be placed in horizontal lifts not exceeding twelve (12) inches in loose thickness and compacted to a minimum of 90 percent of its laboratory maximum dry density. The maximum dry density should be determined in accordance with ASTM Test Designation D-1557 (Modified Proctor). The fill materials should be placed at or near the optimum moisture content. Fill under wavements and walks should also be placed in horizontal lifts and compacted to 90 percent of maximum density except for the top twelve (12) inches which should be compacted to 95 percent of maximum density. Foundations In our opinion, the proposed fueling canopy can be supported on a conventional spread and continuous footing foundation bearing on the competent native soils or on structural fill. Based on the subsurface information obtained at the site, the competent native soils should be encountered below a depth of approximately four feet. As mentioned previously, the existing fill can be considered for use as structural fill, provided the soil can be compacted to the specifications of structural fill. Earth Consultants, Inc.