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EXCAVATE IREF ILL The excavate/refill procedure involves removing unsuitable materials, placing compacted fill, and then building a structure on the compacted fill. The excavation and the fill should extend out beyond the limits of the pro- posed structure, into an "oversize" zone. This zone accommodates lateral stress distribution. The oversize zone is defined by planes extending down from the structure to the beari ng stratum or basal soil. As a general guide- 1 i ne, the pl anes shoul d extend down at a 45 degree angl e (i .e. a one-to-one oversize ratio) from the base of the structure. For footings, the fill should not start immediately next to the footing. As a general guideline, the separation distance should be at least 1/2 the width of the footing. Generally, earthwork excavation and filling should be tested by a geotechnical engineer. Refer to the sheet "Earthwork Testing" for further information. Fill material should be inorganic and unfrozen. The excavate/refill procedure is less expensive than a deep foundation system when the thickness of unsuitable soil is comparatively shallow. Disadvantages of the excavate/refill method include: 1) The cost (including testing) increases if the excavation extends below the groundwater table, due to flow of water into the excavation and into the fill. The actual cost depends on the depth of excavation and the type of material present below the water table elevation. Two examples are: If the depth of excavation below the water table is shallow (less than about 51), and if the surrounding material has low permeability (clayey soil, for example), and the rate of water inflow is low, then the water can be controlled by sump pumping or without any special p rocedu res. If the depth of excavation below the water table is deep (more than about 101) and if the surrounding soil is sandy or contains many sand layers, and the rate of water inflow is high, special procedures may be required for dewatering, excavating, filling, and testing. 2) The oversize may not be attainable due other structures. For foot i ngs, thi s lowering footing elevations. This required in oversizing. to proximity of property lines or di sadvantage can be countered by reduces the horizontal distance ,. ,... r Oi""l TI