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Elk Creek Mine Subsidence Page 2 February 26, 2003 mining height above a longwall coal panel, 108-ft for the maximum 12-ft high longwalls. Peng (1992) provided predictive equations for the fracture Zone height above longwall panels based on rock compression strength. The compression strengths of immediate "D" Seam roof and floor rock, reported in Appendix D, indicate both "Hard and strong rock" and "Medium hard rock". Peng's equations predict that the fracture zone above the roof of the planned 12-ft high longwall panels should not exceed 188-ft, but probably will exceed 126-ft. All available collapse predictions indicate that longwall panels should not hydrologically connect the ground surface to the underlying workings, i.e. water should not be diverted into the Elk Creek Mine from either Bear Creek or Elk Creek. Trough subsidence, as shown on Figures 3 and 4, is the only type of subsidence that should affect the ground surface over and adjacent to the planned Elk Creek Mine longwall panels. Trough subsidence of the ground surface will develop over all the individually mined longwall panels. The factors which impact the prediction of ground surface trough subsidence over Elk Creek Mine longwall panels include: 1) longwall mining height which is limited to 12-ft by the shearer, 2) overburden depths which influence the ability of the overburden to arch across the 825-ft width between panel ribsides, 3) location of planned longwall panels and gateroads which controls where ground surface impacts will develop and 4) location of underlying and overlying mine workings which reduce the magnitude of ground surface subsidence. Surface subsidence from mining adjacent longwall panels within a panel group will, however, overlap. Mining the panels within Panel Group 1 will not affect the ground surface above the other panel groups. Similarly, mining the panels within Panel Group 3 will not affect the ground surface above the other two panel groups. Vertical surface subsidence from mining Panels #5 through #8 within Panel Group 2 will minimally overlap the ground surface above the eastern end of Panels #12 through #15 of Panel Group 3, as indicated on Plate 8. The overlap will be less than 460-ft and will result in less than 0.9-ft of vertical subsidence in the adjacent Panel Group 2 panels. The predicted trough subsidence will probably not be detectable in the minor overlap areas. Surface trough subsidence and horizontal strains were calculated using the method developed by the British National Coal Board (1975). Vertical surface subsidence contours were calculated at selected locations above the gateroad, setup room and shield recovery room ribsides. The locations for which calculations are presented in Appendix A are identified by the underlying south (S), north (N), east (E} and west (W) panel ribsides and the distance in -2- •~ i •~ ~~ ,I