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Figure 25 <br /> Subsidence Calculations, Monitoring Point MC-3, 7 North and Longwall <br /> 101 , No. 1 Mine <br /> MC-3 is over 7 North, No. 1 mine, pillared in 1973, in an apparently- <br /> reactivated subsidence zone due to longwall 101 mining in 1977. The <br /> point had not stablized a8 of 8/9/85. The apparent angle of draw to <br /> longwall 102 is nearly 30, so all movement is assumed to be due to <br /> 7 North-101 extraction. Angle is calculated to the 101 tailgate. <br /> Distance from 101 tailgate (x) : 550 ft. <br /> Surface elevation MC-3: 11,127 ft. <br /> Coal elevation, 101 tailgate: 9,087 ft. <br /> Surface elevation over 101 tailgate: 11,127 ft. <br /> Depth to coal (H) : 2,213 ft. <br /> x <br /> � -ly <br /> MC-3 <br /> H <br /> no scale <br /> 8 � <br /> 7 North <br /> longwall 101 A bed <br /> Slope angle (0) : <br /> 0 = tan-1 x _ <br /> = tan-1 173 <br /> 550 <br /> = 17.460 <br /> Apparent angle of draw (8) : <br /> 8 = tan-1 x <br /> Hcos20 <br /> = tan-1 550 <br /> 2213cos217.46 <br /> = tan-1 550 <br /> 2213 0.91 <br /> = tan-1(0.27) <br /> = 15.280 <br />