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0 <br />0.1 <br />0.2 <br />11 <br />S 0.3 <br />W <br />0 0.4 <br />1- <br />0.5 <br />W 0.6 <br />Z 0.7 <br />W <br />0 0.8 <br />(7) <br />CO 0.9 <br />D <br />1.0 <br />0 <br />0.2 <br />0.4 <br />0.6 <br />0.8 <br />W/d <br />1.0 <br />1.2 <br />1.4 <br />1.6 <br />18 <br />Figure C. Graph showing subsidence factors (a = S /t) versus mining panel width to depth <br />ratios (W /d) for the West Elk longwall mine (squares), 1972 to 1976 Somerset room - and - pillar <br />mine (circles), and the York Canyon, New Mexico longwall mine (diamonds), along with the <br />average National Coal Board (NCB) longwall curve. Topographic effects on subsidence factors <br />for the York Canyon, New Mexico longwall mining area (upper point of measurement was in a <br />deep draw; middle point was on an isolated ridge; lower point is maximum for area). <br />