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• (3) To help prevent base sliding in fills from an increase in pore water pressure, all fills <br />should be placed on ground that is completely cleared of vegetation and root growth. <br />The ground surface should be benched if the natural slope is more than 20 percent. <br />Benches with 1:1 inclination, about 8 feet wide, at 4 to 6-foot height intervals can be <br />used. Where available, boulder rabble with a wide range of sizes would be acceptable <br />for use as a starter fill at the toe of the fill. Phis is an excellent use for such a material <br />because of its strength and drainage capability. However, due to the potential for fines <br />migration into a boulder fill, where boulders are used, an acceptable filter fabric should <br />be placed over the rubble fill prior to starting general filling operations. At any location <br />where a fdl crosses a drainage feature of any kind, we recommend some provision to <br />carry water through the fill, such as a drainage blanket or culvert. Minor, tributary <br />• drainage features may be cut off with compacted clay cut-off walls and diverted upstream <br />of the fill. <br />(4) All unsuitable topsoil, organic material, debris or soft soils should be removed from the <br />area to receive fill. <br />(5) Natural soils in areas to receive till should be scarified 6-8 inches, moisture conditioned <br />if necessary, and compacted to the same level as the overlying fill. <br />(6) All fill and backfill should be approved by the geotechnical engineer, placed in uniform <br />lifts with a thickness compatible with the type of compaction equipment being used, <br />moisture conditioned to within -2 and +3 % of optimum and compacted with the <br />- appropriate equipment. Fill specifically used under interior floor slabs should be <br />moisture conditioned to optimum moisture content or above. Even properly compacted <br />• 15 <br />