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-13- <br /> with existing fill is not acceptable, existing fill should be removed to <br /> expose native inorganic soil , and the exposed surface should be com- <br /> pacted to at least 90 percent relative compaction. <br /> Fill Placement and Compaction: All fill in playfield areas should be <br /> placed in loose lifts not exceeding 8 inches in thickness, moisture con- <br /> ditioned to near optimum moisture content for compaction, and systema- <br /> tically compacted to at least 90 percent of the maximum dry density. <br /> Similar compaction criteria are recommended for areas that are to be <br /> paved, except that the top 2 feet of fill should be compacted to at <br /> least 95 percent of the maximum dry density. In areas to support struc- <br /> tures, all fill should be compacted to at least 95 percent relative <br /> compaction. <br /> Fill Material Source: On site inorganic soils (primarily tills) should <br /> be suitable for use as fill , provided the moisture content is properly <br /> controlled to allow compaction to the specified criteria. Laboratory <br /> tests indicate that average in-place moisture contents for unweathered <br /> and highly weathered till were about 6 percent and 9 percent above <br /> optimum moisture content, respectively. Thus, moisture control is <br /> expected to consist primarily of drying natural soils. <br /> If existing fill soils are excavated, they should also be suitable for <br /> reuse as fill if they are properly processed. Processing should consist <br /> of removing organic soil portions and branches and roots, and moisture <br /> conditioning. <br /> Based on the laboratory test results and our experience, we expect that <br /> highly weathered till , if used for compacted fill , will experience a net <br /> decrease in volume, relative to its natural condition; and that the un- <br /> weathered till will experience a net increase in volume, relative to its <br /> natural condition. Appropriate "shrink" factors for highly weathered <br /> till are 10 and 15 percent for 90 and 95 percent relative compaction, <br /> respectively. Appropriate "bulk" factors for unweathered till are 10 <br /> and 5 percent for 90 and 95 percent relative compaction, respectively. <br />