10630 EVERGREEN WAY BASE FILE 2016-01-01 MF Import

Geotechnical Engineering Report Proposed New Storm Water Vault Northwest Mitsubishi Novembcr 18, 2002 CG Pile No. 1397 Page 4 631.5 feeQ. Aclow the fill was a weathered zone that was loose to medium dense wiih trace organics. The surface water was trickling into the tcst holes and the excavated material was wet and ran into the excavation. Iivaluation of the bottom of the holes was JitficulL [n Test Pit t at a depth of 8.5 feet, the material appcared to be a b�ray sand wiPi silt to silty sand that was medium dense to dense. "Cest Pit 2 could not bc advanced into medium dense or better soils. It was not possible to detcrminc thc amount of subsurfacc watcr sccpagc in the holcs. CONCLUSIONS ANll RECOMMENDATIONS General The sile is considercd suitaUle for the planned improvements. The nati��e soil at depth appcars to be mcdium dense to dense soil that should provide good support for the planned strucwre. We expect that, due to �vct conditions and the depth to medium dense or better soil, some overexcavation under the vault and replacement with rock matcrial such as 2- to 4-inch rock spalls will be needcd. 1��c recammend that budgets plan for at least 9-inches of rock undcr the slab areas and at �cast 18-inches of rock under the footing areas. The rock spalls coutd be cappcd with 2-inches of tiner crushed rock for a better working surface. 'Che rock luyer may also be needcd duc to tf�c depth to suitable Uearing soil. Our explorations indicated that the elevation of suitable mcdium dcnse or better soil may be slightly bclow the planncd Pooting location. Winter scason grading is planned. Most likely backfill will be completed with soils that are highly moisture sensitive and dif5cult to compact when wet of optimum moisture. The parking arca crcated by the planned improvcmcnts is expccted to be gravel covered. We ha��c becn informed that sctHcment of thc backfill would be acceptable and could bc repaircd with importing of morc gra�cl. The lateral pressures acting on the structure will depcnd on Ihe materials used. We present two scts of figures — one assuming relatively poor compaction using silty sand from the site and importcd into thc site. Another set of figures assumes compaction meets at leasl 90 percent of maximum dry density based on ASTM D 1557. W� cxpect that compaction to 90 percent a�ill be difficult to achic��c wiih the planned construction sciiedule and expected conditions. Cornerstone Geotechnicaf, Inc. 5�l /!4 /