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• made into native soils and any oversized (6-inch) materials should be removed from the exposed subgrede. The sand bed should be thoroughly compacted to at least 70 percent relative density (ASTM D4253 and ASTM D4254). A clay cap should be provided on the outside of the tanks. An allowable bearing pressure of 5,000 psf can then be used. The water tank can also utilize a ring beam foundation if desired. This can be fmalized once the pads are completed for these features. Downhill Conveyor: We understand that the loads imposed by the downhill conveyor would typically be founded on concrete or timber ties staked to the ground, at approximate 12-foot intervals. Longer spans are possible with foundation systems bearing below depths at which moisture might be expected to penetrate. Because of the moisture-sensitivity of the subgrade soils, we recommend the foundation system consist of drilled piers bearing in relatively stable • soils below the depth of anticipated moisture penetration. We recommend that the drilled piers be designed to bear at least 5 feet below fmished grade, and be at least 12 inches in diameter. An allowable vertical bearing pressure of 5,000 psf and side shear of 500 psf (below a depth of 1.5 pier diameters or 3 feet, whichever is deeper) can be used to design the piers. Higher bearing pressures can be used if deeper piers are utilized. For lateral stability calculations, a modulus of horizontal subgrade reaction of 50 tcf, or a passive earth pressure of 300 pcf, in terms of equivalent Fluid pressure, can be used below 3 feet. The upper 3 feet should be ignored for axial and lateral stability calculations. Another option for the conveyor foundations would be to trench and pour concrete grade beams into the native soils below the estimated 3-foot frost depth. Allowable bearing pressure would be about 3,500 psf. Conventional spread footings or pads are also an option, but would .. 20