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Elk Creek Mine Subsidence Page 36 February 26, 2003 <br />The average gateroad pillar stresses were assumed to be sufficient <br />• to crush the gateroad pillars sometime after the second adjacent <br />panel is mined past. <br />Abel and Lee's method, shown graphically on Figure 12, was <br />modified for an overburden density of 151 PCF instead of their <br />original assumption of 199 PCF. The adjustment applied was to <br />change the overlying rock density constant, from 0.0226 Mpa per <br />meter of depth for 194 PCF to 0.0235 Mpa per meter of depth for the <br />151 PCF mean measured immediate roof and floor rock densities <br />presented in Appendix D. The following example for the gateroad <br />pillar between Panel #2 and Panel #3 at 1,000-ft (305 m) of depth <br />explains the method. <br />.___ o.oz3sroecena-_ o.oz3st3os~ = 8.625 MPa (1250 si <br />Lmax 1-Extraction - 1-0.169 -- _ p ) <br />Lmax (w ) = 8 .625 (120) = 0.683 <br />Subsidence() = 1.39 + 5.57(0.683] = 5.19$ <br />Subsidence(ft) = 1'oo (9.5) = 0.99-ft (Table 5) <br />Predicted vertical ground surface subsidence resulting from <br />crushing of gateroad pillars between Panel Group 1 longwall panels <br />' ranged from approximately 0.3-ft at the 350-ft depth where the <br />• north side of Panel #1 will cross under Bear Creek to approximately <br />0.9-ft where Panel #2 and Panel #3 gateroad will pass under the <br />2,000-ft overburden contour. The total vertical surface subsidence <br />' over the interior gateroads was obtained by adding the predicted <br />trough subsidence from each adjacent individual panel over the <br />gateroad pillars to the predicted vertical ground surface <br />' subsidence resulting from crushing of gateroad pillars. The total <br />predicted maximum subsidence over the interior gateroad pillars <br />ranged from 2.0-ft where Bear Creek crosses over the north side of <br />' Panel #1 to 2.9-ft in the 2,000-ft depth area between the Panel <br />#2/Panel #3 gateroad. The Panel Group 1 ultimate maximum predicted <br />surface subsidence contours after interior gateroad pillar failure <br />~ are plotted on Plate 5. <br />Predicted vertical ground surface subsidence resulting from <br />' crushing of gateroad pillars between Panel Group 2 longwall panels <br />ranged from approximately 1.8-ft at the 1,700-ft depth near Station <br />N-7,750V on the north side of Panel #5 to approximately 2.8-ft <br />where Panel #10 and Panel #11 gateroad will pass under the 2,800-ft <br />' overburden contour. The total vertical surface subsidence over the <br />interior gateroads was obtained by adding the predicted trough <br />subsidence from each adjacent individual panel over the gateroad <br />' pillars to the predicted vertical ground surface subsidence <br />resulting from crushing of gateroad pillars. The total predicted <br />• maximum subsidence over the interior gateroad pillars ranged from <br />' S.5-ft where Bear Creek crosses over the north side of Panel #5 to <br />-36- <br />