Specifications include, but are not limited to: The proposed school and field house buildings may be supported on shallow spread footings designed for a maximum net allowable bearing pressure of 3,000 pounds per square foot (psf). Minimum widths for wall footings of 24 inches and column footings of 36 inches are recommended when design based on 3,000 psf results in a narrower footing. For the school building, settlement on the order of 1-inch total and ½-inch differential can be anticipated, based on the assumed loads of 3 to 5 kips per linear foot for walls and maximum column loads of 100 to 150 kips. For the field house, settlement on the order of ¾-inch total and ½ inch differential can be anticipated, based on the assumed loads of 2 kips per linear foot for walls and 75 kips for columns. Exterior footings should be founded a minimum of 32 inches below the final exterior grades to provide protection from frost action. Footings should be supported on new compacted structural fill or medium dense/stiff natural soils. If loose or soft natural soils or undocumented, uncontrolled fill are encountered at the footing subgrade elevation, these soils should be undercut to suitable materials. The undercut volume should be backfilled with compacted structural fill, AASHTO No. 57 aggregate, or additional concrete. The aggregate should be placed in 1- to 2-foot-thick layers and be tamped with the equipment bucket with the last lift compacted with a small walk behind vibratory roller or large vibra-plate. GTA recommends that footing excavations be filled with concrete the same day the excavations are performed to prevent destabilization and softening of the subgrade soils. Detailed foundation excavation evaluations should be performed in each footing excavation prior to the placement of crushed stone, reinforcing steel, or concrete. These evaluations should be performed by a representative of the registered Geotechnical Engineer to confirm that the design allowable soil bearing pressure is available. The foundation bearing surface evaluations should be performed using a combination of visual observation, hand-rod probing, comparison with the borings, and Dynamic Cone Penetrometer (DCP) testing, as applicable.
