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• content and low swelling potential, spread footing foundations with a minimum dead load and <br />maximum allowable bearing pressure often work well. Industrial buildings may utilize a <br />trenched grade beam foundation, if structural loads work with the allowable bearing pressures. <br />Reinforcing steel is hung in the trenches, and the floor slab can be structurally continuous with <br />the walls on sites where the subgrade soils are non to low swelling. The advantages of trenched <br />grade beams include pouring concrete directly against a trench wall, therefore, no backfill and <br />a preferential path for exterior moisture to infiltrate the subgrade. The grade beams also have <br />very high stability laterally and vertically when poured against the rough, stiff trench walls. <br />Trenching for grade beams can be difficult where sandstone boulders are present. Although we <br />found the boulders generally easy to penetrate with an auger drill. <br />The following sections present foundation recommendations for various types of <br />• structures that can be considered preliminary in nature, except where noted. <br />Coal Loadout Silo, Stoker Bin: The coal loadout silo and stoker bin can be placed on a mat <br />foundation designed for a maximum allowable bearing pressure on the order of 5,000 psf, <br />assuming total and differential settlement of 1-inch can be accommodated. Dead load should be <br />kept as high as practicable. The mat should be placed on native very stiff clay soils or similar <br />compacted fill at least 4 feet below fmished exterior grade. The truck loadout area could have <br />existing fill from demolished structures that previously occupied the site, which should be <br />completely removed from foundation areas. <br />Water Tank: The water tank can be phtced directly on a bed constructed of clean, free-draining <br />sand. Preliminarily, we estimate that the bed should be at least 36 inches deep and extend <br />laterally from the tank for a distance equal to the depth of the sand. The excavation should be <br />y <br />19 <br />