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~J <br />-20- <br />valley fill caused by foundation failure. <br />Method of Construction <br />Placement and compaction of the fill considerably influences <br />its overall strength characteristics. Additionally, the perfor- <br />mance of the fill from a point of view of permeability can be sig- <br />nificantly affected by the method of construction. We anticipate <br />that these fills will be constructed hauling the spoil rock from <br />the active mine area to the disposal site with large mine trucks, <br />probably in the range of 100-ton carrying capacity. Fill should be <br />placed in approximately horizontal lifts with the initial con- <br />• struction to start at the toe of the valley fills. Where possible, <br />large rock in the spoil should be pushed to the edges of the fill. <br />Compaction of the fill is necessary in order to achieve the <br />strength parameters assumed in this analysis. We anticipate place- <br />went in approximately 4-foot lifts and compaction to about 90 <br />percent of AASHTO T-99 density. We expect the average moist weight <br />of the fill in-place to be on the order of 125 pcf. Construction <br />control of spoil disposal site is relatively new. We suggest an <br />observational procedure during the early stages of construction <br />to determine a method of compaction which will yield the desired <br />degree of compaction and be compatible with the mine operation. We <br />anticipate dumping from haul trucks and spreading the lifts with <br />dozers or similar equipment. Compaction can probably be achieved <br />• by routing the haul trucks over the active fill surface. It may <br />