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1 LOWRY &. ASSOCIATES Page 6 August 17, 1990 L & a No. 90-190 Site earthwork should be prepared in accordance with the recommendations of this report. A representative of our firm should be present during grading operations to determine compliance with job specifications. Residential and Clubhouse Foundations The proposed residences may be supported upon continuous and isolated spread 1 foundations based in native undisturbed soils, newly constructed engineered fill, or a J combination of those materials. Foundations should extend at least 12 inches below finished subgrade and should be at least 12 inches wide. Foundations designated as above may be designed for maximum allowable soil pressures of 1500 pounds per square foot for dead load, 2300 pounds per square foot for dead plus live load, and 3000 pounds per square foot for total load, including the effects of either seismic or wind forces. The weight of foundation concrete extending below grade may be disregarded in sizing computations. Resistance to lateral foundation displacement may be computed using an allowable friction factor of 0.35 acting at the foundation level. Additional lateral resistance may be derived through the development of passive earth pressure equivalent to a fluid weighing 200 pounds per cubic foot acting against any vertical foundation face. These two modes of resistance should not be added unless the larger value is reduced by 50 percent since mobilization of these resistances may occur at different degrees of horizontal movement. Bridge Abutment Foundations It is recommended that either shallow spread foundations, drilled piers or driven piles be used to support the bridge abutments. Shallow spread foundations may be considered if they are completely protected against scour from the river. Spread foundations used to support the bridge may be designed for maximum allowable soil pressures of 2000 pounds per square foot for dead load, 3000 pounds per square foot for dead plus live load, or 4000 pounds per square foot for total load, including the effect �t of either seismic or wind forces. Foundations should be a minimum of 24 inches wide 1 and a minimum of 24 inches deep. The weight of foundation concrete extending below grade may be disregarded in sizing computations. IIt is anticipated that spread foundations will be the most economical foundation system. Therefore, we are not including specific recommendations for either drilled piers or driven piles. If the design warrants drilled pier or driven pile foundations, we can ! provide recommendations with regard to depth, bearing capacity and lateral resistance.