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c <br />October 23, 2007 G-2611 <br />1030 N. Park Drive, Everett, WA Page 4 <br />Geologically Hazardous Areas: Geotechnical Letter <br />111c following foundation design criteria are appli::able to spread footing foundations that are <br />supported as described above: <br />• Allowable bearing pressure, including all dead and live loads: <br />• Minimum depth to bottom of perimeter footing below <br />adjacent final exterior grade: <br />• Minimum depth to bottom of interior footings <br />below top of floor slab: <br />• Minimum width of strip footings: <br />• Minimum lateral dimension of column footings: <br />• Estimated post -construction settlement: <br />— Across building width: <br />2,000 psf <br />= 18 inches <br />= 12 inches <br />= 16 inches <br />= 24 inches <br />= 1/2 inch <br />= 1/2 inch <br />A one-third increase in the above allowable bearing pressures can be used when considering <br />short-term transitory wind or seismic loads. Lateral loads can also be resisted by friction <br />between the foundation and the supporting compacted till subgtade or by passive earth pressure <br />acting on the buried portions of the foundations. For the latter, the foundations must be poured <br />"neat" against the existing undisturbed soil or backfilled with a compacted fill meeting the <br />requirements of structural fill. Our reconuncnded parameters are a: follows: <br />- Passive Pressure (Lateral Resistance) <br />• 350 pef equivalent fluid weight for dense site soils and structural fill <br />- Coefficient of Friction (Friction Factor) <br />0.35 for dense site soils and structural fill <br />Garage Slab <br />Subgrade support for slab -on -grade floors should be prepared as recommended for foundations. <br />For dry storage, slab -on -grade floors should be placed on a capillary break to prevent wicking of <br />GEO Group Northwest, Inc. <br />;6 <br />