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Figure 21 <br /> • - - <br /> Subsidence Calculations , Control Points TP 2 and TP 4, Monitoring Point <br /> MC-8 and Longwall 301 <br /> TP-2, TP-4 and MC-8 are marginal to longwall face 301; TP-4 appears to <br /> be almost stablized (last movement -0.06 ft, measured 8/9/85) . 301 <br /> face stopped early 1981. TP-4 is directly ahead of tailgate corner. <br /> TP-2 (not subsided) is northwest of headgate corner. MC-8 (not <br /> subsided) is southwest of headgate entry, 790 ft from panel margin. <br /> TP-4: <br /> Distance from tailgate to TP-4 (x) : 340 ft. <br /> Surface elevation TP-4: 11,730 ft. <br /> Coal elevation at tailgate: 9,215 ft. <br /> Surface elevation over tailgate (from 1"=1,000' topo/mine map) : 11,480 ft. <br /> Depth to coal (H) : 2,265 ft. <br /> TP-4 x <br /> 0-1 <br /> y <br /> no scale <br /> 8 H <br /> • longwall 301 A-B bed <br /> Slope angle (0) : <br /> 0 = tan- <br /> 1 Y <br /> x <br /> = tan-1 250 <br /> 340 <br /> = 36.33° <br /> Angle of draw to TP-4 (A; subsided) : <br /> 9 = tan-1 x <br /> Hcos20 <br /> = tan-1 340 <br /> 2265cos236.33 <br /> = tan-1 340 <br /> 2265 0.65 <br /> = tan-1(0.23) <br /> = 13.020 <br />