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NWO *Moe 23 materials are totally removed and replaced. However, the differential settle- ments will be less and allowable bearing pressures will be greater than if the total thickness of shallow materials are left in their present condition. Removal Depths. The appropriate depth of excavation and replacement will depend on the type, size, loads, and allowable settlements for the structure or equipment. The minimum depth of removal should comply with the following pro- visions: o At least 4 ft below the existing ground surface, o At least 4 ft below the bottom of the footing or foundation pad which bears in the fill, or o At least one-half times the minimum footing or foundation pad width, below the base of the foundation width. Actual depths of removal should consider the structure and equipment layout, load levels, and allowable settlements. Estimated settlements for various loads, footing sizes, and removal depths are presented subsequently. Deeper removal depths than shown above will be necessary for some structures and equipment. Replacement Material Requirements. The excavated materials should be replaced with import or on-site material meeting the requirements for structural fill. These requirements are presented in the Earthwork section of this report. On-site silty sand, which is free of deleterious material, is acceptable for structural fill. From a geotechnical standpoint, it is acceptable for the structural fill to contain up to 20 percent (by volume) glass fragments, provided the maximum size of glass fragments meet the criteria discussed in the Earthwork section of this report. The material should be -placed and compacted to meet requirements for structural fill. Fill Reinforcement. The bearing capacity of the fill can be increased if the structural fill, below foundations, is reinforced. The reinforcement should consist of Tensor SS-2, Exxon Chemicals Americas GTF 275D, or similar geotextile, which should be placed at 6-inch depth intervals from the base of the foundations and pads to the exposed surface after excavation. The reinforcement should extend laterally to no less than 10 feet beyond all sides of the foundations. Alternately, the reinforcing geotextile can be placed on an areal basis. By providing a level of tensile reinforcement to the fill, the geotextile will help to better distribute loads and reduce differential settlements. 1144A/CC-23 ',::McClelland