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0 0 <br />0.1 <br />e 0.2 <br />UO <br />I! <br />0.3 <br />® 0.4 <br />U <br /><? 0.5 <br />0.6 <br />W 0.'7 <br />as <br />I-Q 0.0 <br />.J <br /> <br />Sor nerset Mine <br />o West Elk Mine <br />NC3, 1975 <br />1.0 L <br />0 <br />O <br />O <br />0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 <br />W/d <br />Figure 4. Graph showing subsidence factors (a = Sm/t) versus mining panel width to depth ratios <br />(W/d) for the West Elk longwall mine (squares), 1972 to 1976 Somerset room-and-pillar mine <br />(circles), and the York Canyon, New Mexico longwall mine (diamonds), along with the average <br />National Coal Board (NCB) longwall curve. Topographic effects on subsidence factors for the <br />York Canyon, New Mexico longwall mining area (upper point of measurement was in a deep <br />draw; middle point was on an isolated ridge; lower point is maximum for area). <br />Tetra Tech - 090717/P 44