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• <br />0 <br />0.2 <br />0.4 <br />S/S m <br />0.6 <br />0.8 <br />1.0 <br />P <br />0 <br />NCB, 1975 0 , <br />-1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 <br />X/d <br />Figure 9. Subsidence development curves relative to a point (P) from the 5NW longwall panel at <br />the West Elk Mine (squares), and Somerset room - and -pillar (circles, subsidence more than 90 <br />percent complete and triangles, subsidence only 60 percent complete) as compared to the average <br />National Coal Board curve (1975). This relationship is shown as the ratio of subsidence to <br />maximum subsidence (S /S m ) versus the ratio of face position to overburden depth (X /d). <br />