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.. 1..H. KLEINFELDER & ASSOCIATES File No. S-2314-1 August 15, 1978 PAGE TEN i Engineered Fill is 90 percent of the above referenced maximum = dry density. Where native soils are used as Engineered Fill , the recommended degree of compaction is between 85 to 90 percent.p In areas to receive slab-on-grade floors g it is recommended that the native soils placed as fill be compacted at a moisture content of at least 5 percent above the optimum soil moisture. As noted earlier, it was recommended that slab-on- . grade floors be supported by a minimum of 18 inches of moisture-conditioned soil . Based on our field explorations and assuming minimal site grading, it is likely that the soils to be moisture-conditioned will probably consist of the native dark-brown to black silty clay soils . Several methods exist to establish moisture to the 18-inch depth. In our opinion, long term flooding or sprinkling with dikes to control runoff generally produces uniform results . This method can take time, however, often on the order of three ' weeks . Alternatively, if time is a factor, the surface clay can be processed by mechanical means . We recommend that deep scarification to 18 inches not be allowed. In order to provide more uniform results , we recommend that the black clay soils be moisture-conditioned in at least three lifts . This would mean that the upper approximate 12 inches of native soils would have to be removed in order to moisture condition the lower Portion. We recommend that this lower portion be scarified, moisture-conditioned and recompacted to between 85 and 90 percent Of the maximum dry density as determined by the ASTM D-1557-70 test procedure. This recompaction should be done at a moisture content of at least 5 percent in excess of the optimum soil moisture. The native soils that have been removed should perferably bero Off site and placed according to the above recommendations.Cessed