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Ip ` Indian River County Page 8 Project No . 00- 11493 . ' Foundations designed . and constructed in accordance with these recommendations are expected to sustain tolerable total and differential settlements . r Observation Tower 4 Provided that the structure loads of the observation tower do not exceed those stated for the restroom buildings , the observation tower may be supported on shallow foundations designed for an allowable bearing pressure of 2 , 500 psf ' and constructed in accordance with the I previous recommendations for the restroom 'buildings. The allowable bearing pressure refers to dead and live loads and - reflects a net increase in pressure over and above that exerted by the overburden soils. Consequently, the weight - of the foundation concrete and soil backfill may be neglected in the sizing _ x g g computations. A 25 percent increase in the allowable bearing pressure is permissible for total loads, including those due to wind forces . Foundations subject to lateral forces arising from wind loads will - resist those forces through a combination of base shearing resistance and earth pressure, that acts on the vertical foundation faces located opposite . and at right angles, to the direction of thrust. Base ." shear resistance . should be determined using a friction factor of 0A Earth pressure resistance provided by well-compacted submerged granular soil (below the water table) should be computedbased on an equivalent fluid pressure of. 180 ' pounds per square , foot per foot of depth. . Lateral i resistance determined in accordance with the above should be considered an ultimate value and appropriately factored for safety.. We recommend using a safety factor of at least 1 . 5 , For shallow foundations, resistance to uplift forces will be provided by the dead weight .of the structure , the foundations and the soil overlying the foundations. For design purposes, the unit_ weight of moist soil backfill maybe taken as 110 pounds per cubic foot (pcf) . A lower i unit weight of 60 pcf should" be used for submerged soil backfill. Preliminary allowable capacities for a driven, 20-foot long concrete ' or timber . . pile are provided below for evaluation , of a deep foundation system for support of the observation tower. Pile Type, and Size . Allowable Capaefties. tons Compressive II lit Lateral 14 " square, prestressed, precast concrete 30 13 1 . 5 ` Timber with minimum tip diameter of 6" and minimum butt 12 6 0 .5 diameter of 12 " * Resisting force acts at pile head 4