6400 36TH AVE W 2018-01-02 MF Import

DAMES & MOORE .4 rF,,tt» •, n, rt.i,raa,:a Fs.ar The Boeing Company August 2, 1989 Page 4 dry density based on ASTM D-1557. Permanent slopes constructed of compacted fill should be no steeper than 2 to I (horizontal to vertical). We have considered the suitability of using the excavated glacial soils as fill material. These soils typicall: contain fines (silt and clay sized particles passing the No. 200 sieve) in excess of 30 percent. Although dense in their native state, they are very sensitive to an increase in moisture content. Whc:t excavated, they would soften very quickly if subject to rainfall or water from ary other source. As a result, we recommend that the native till soils be used for compacted fill only if the filling operations are accomplished in the drier season of the year. If filling must be done during the wetter season, we recommend that imported clean well -graded sand or sand and gravel be used. The soil fraction passing the No. 200 sieve should be limited to approximately 5 percent. I If it is necessary to carry out construction activities during wet weather periods; we recommend that prepared subgrade soils be covered with crushed rock surfacing. Construction traffic should be routed away from these areas to further reduce the potential for deterioration of prepared areas. If prepared areas are not covered with crushed rock, we ecommend that the exposed surface be sloped to drain and that heavy construction equipment be kept off the surface during wet weather conditions. Foundation Sunoort We recommend that the proposed Recreation Building be supported on conventional spread footings bearing on native glacial soils or on compacted fill placed as , recommend above. We recommend that footings founded in compacted fill or the upper silty sand layer be designed for an allowable soil bearing pressure of 3,000 psf. Footings founded 1 on weathered till may be designed for an allowable bearing pressure of 5000 psf. These values are intended to apply to the total of all normal dead and live loads and may be increased by one-third for short-term wind or seismic loading conditions. Continuous and individual footings should have minimum widths of 18 and 24 inches, respectively, and be 1 founded at least I8 inches below the lowest adjacent grade. ? We estimate that post -construction settlements of footings supported as recommended on compacted fill and native weathered till soils will be about 1/4-inch. For footings supported on undisturbed and unweathered till, we anticipate post -construction settlements to be negligible. Differential settlement between foundation elements should not exceed 1/4-inch, provided the recommendations outlined above are followed. Floor Slab and Pavement Support: Based on the resultsof ourexploration program and previous experience in the vicinity, we have selected recommended K and CBR values for use in design of floor slabs and flexible pavements. Our recommended design K. and CBR i values are presented in Table 1 below. J