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WA <br />soils, and the resulting overexcavation should be backfilled with lean <br />concrete or compacted structural fill as recommended above. The base of all <br />excavations should be dry and free of loose soil when placing concrete. <br />Spread footing foundations constructed on the native glacial till subgrade may <br />be designed for maximum net allowable soil bearing pressures of 8,000 pounds <br />per square foot (psf). Footings which require overexcavation and replacement <br />with structural fill, either glacial till or imported granular material, <br />prepared as described above may be designed for maximum net allowable soil <br />bearing pressures of 5,000 psf. All footings should have a minimum width of <br />two feet and be founded at least 18 inches below adjacent exterior finished <br />grades. The footing contact pressures from eccentrically applied loads should <br />not exceed these maximum values. However, the allowable bearing pressures may <br />be increased by one-third for short=term loads such as those from wind or <br />earthquakes. <br />Foundation settlements should be elastic and should occur as the loads are <br />applied. We expect that differential settlement should not exceed 1/4 inch <br />for individual footings and 1/2 inch between adjacent foundations. Total <br />settlements should not exceed about 1/2 inch. <br />Lateral loads will be resisted by friction -along the base of footings and by <br />passive soil resistance against buried spread footing foundations. A <br />coefficient of friction between cast -in -place concrete and undisturbed natural <br />soil or structural fill of 0.5 is recommended. Passive resistance of <br />compacted backfill may be determined using an equivalent fiuid density of 355 <br />pounds per cubic foot (pcf). This value includes a factor of safety of 2. <br />Slab foundations may be constructed on native glacial till soil, re -compacted <br />glacial till soil, or imported structural fill with the net bearing pressures <br />given above. Loosened material from excavation of the bearing surface should <br />be re -compacted to at least 95 percent of the maximum dry density as deter <br />mined by ASTM D-1557. The bottom of the slab can bear on the top of the <br />native ground surface provided this surface i's'undisturbed or on -a surface <br />consisting of properly re -compacted glacial till or imported fill. <br />Converse Consultants NW <br />