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Page 8 <br />LEROY CRANDALL <br />AND ASSOCIATES <br />thickness of relatively non-expansive soils at two feet.) A suggested grada- <br />tion for the gravel layer would be as follows: <br />Sieve Size Percent Passing <br />3/4"90 - 100 <br />No. 4 0 - 10 <br />No. 100 0-3 <br />If the membrane is used, a low-slump concrete should be used to minimize possi- <br />ble curling of the slabs. The concrete slabs should be allowed to cure properly <br />before placing vinyl or other moisture-sensitive floor covering. <br />PAVING <br />To provide data for design of asphaltic paving, California Bearing <br />Ratio.tests were performed on two samples of the on-site soils. The tests <br />indicate a C.B.R. value of 2 at 90% compaction. This *value is low and indi- <br />cates that the upper natural soils have relatively poor characteristics from <br />a paving standpoint.Compaction of the subgrade to at least 90%, including <br />trench backfills, will be important for paving support.Also, the moisture <br />content of the subgrade soils will be critical since the soils are expansive <br />clay materials; the moisture content of the subgrade should be at optimum mois- <br />ture content or slightly above when placing the base course. <br />Assuming·that the paving subgrade will consist of the on-site soils <br />compacted to at least 90% as recommended, and that the subgrade will be at a <br />unifofm moisture content of optimum or above, parking areas subject to automo- <br />bile traffic may be paved with two inches of asphaltic paving and four inches <br />of base course placed on the compacted subgrade.Driveways and areas subject