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Page 7 <br />L£ROY CRANDALL <br />AND ASSOCIATES <br />90%.It is recommended that the moisture content of the on-site soils used in <br />fills not be below optimum and not more than 4% above optimum moisture content <br />at the time of compaction.Imported relatively non-expansive granular soils <br />should be compacted at a moisture content varying no more than 2% below or <br />above optimum moisture content. <br />Because of the expansive nature of the on-site soils, we recommend <br />that at least the upper two feet of fill beneath the planned building floor slab <br />and any adjacent concrete walks and slabs consist of imported relatively non- <br />expansive and predominantly granular soils such as a silty sand. The on-site <br />soils, less any debris or. organic.matter within any existing fill, may be used <br />in the required fills except for the upper two feet of fill in the building area <br />and beneath adjacent walks and slabs. Due to their expansive nature, proper <br />control of the moisture content will be required when using the on-site soils. <br />The excavation of the upper natural soils, the premoistening. of the <br />soils, and the compaction of all fill should be inspected and tested by our <br />firm.Imported fill materials should be approved prior to importing. <br />FLOOR SLAB SUPPORT <br />If the subgrade is prepared as recommended, and at least the upper two <br />feet of fill consists of compacted relatively non-expansive granular soils, <br />the building floor slabs may be supported on grade.If vinyl or other moisture- <br />sensitive floor covering is planned, we would suggest that the slab be sup- <br />ported on a four-inch-thick layer of gravel or on an impermeable membrane as <br />a capillary break. (If the gravel is used, the thickness of underlying select <br />relatively non-expansive soils may be reduced to 20 inches, keeping the total