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<br />1.0 SUMMARY <br />The proposed mining geometry for Panel C consists of pillars on <br />75-ft by 120-ft centers and a maximum entry width of 20 ft. <br />Table 1 summarizes maximum extraction heights, overburden depths <br />and factors of safety with respect to pillar load carrying <br />capacity and the anticipated load on the pillar. These factor of <br />safety determinations use the Wilson pillar design method for <br />pillar load carrying capacity and tributary area loading for <br />estimated pillar load. <br />Table 1 <br />• <br />• <br />Overburden <br />Depth Range <br />(Feet) Maximum <br />Mining Height <br />(feet) Minimum <br />Safety <br />Factor <br />200-600 18 2.0 <br />600-700 18 1.7 <br />700-800 18 1.5 <br />800-900 17 1.5 <br />A barrier pillar must be left between Panel C and any adjacent <br />mine workings. The width of this barrier pillar is either 100 ft <br />or 140 ft, depending upon the type of adjacent mining. Where <br />Panel C is adjacent to caved areas, the minimum required width of <br />the barrier pillar is 140 ft. Where Panel C is adjacent to panel <br />entries where no caving has occurred, the minimum required width <br />of the barrier pillar is 100 ft. <br />This pillar stability analysis uses existing physical rock <br />properties data from the Orchard Valley mine site and the <br />historical mining experience at the mine site. <br />Cyprus Orchard Valley Mine <br />Panel C Pillar Analysis <br />March 12, 1992 <br />page 1 <br />