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U <br />Cl <br />0.1 <br />s 0.2 <br />rn <br />tl <br />0.3 <br />0.4 <br />Q 0.5 <br />0.6 <br />z <br />0.7 <br />Cn 0.8 <br />co) 0.9 <br />1.0 <br />7 <br />Somerset Mine <br />El West Elk Mine <br />— O <br />NCB, 1975 <br />❑c <br />.7 <br />i <br />0.4 0.6 0.8 1.0 1.2 1.4 1 _E; 1 f <br />Figure 4. Graph showing subsidence factors (a = 1 S./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 />• <br />