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<br /> <br /> <br /> <br /> <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 /> <br /> <br /> <br /> <br /> <br />