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Elk Creek Mine Subsidence Page 27 February 26, 2003 the east recovery room ribside) on the north side of Panel #3. • This location is identified on Figure 9 and the output is listed in Table A8. At cross section N-3,675V, in virgin ground, the 1,000-ft (305 m) overburden (depth to the "D" Seam) contour crosses over the ribside. The seam thickness is 15-ft at this location and the mining height will be limited to 12-ft by the shearer. The panel width is 825-ft (251 m). The panel width/depth ratio equals 825/1000 = 0.825. The calculation steps follow: 1) The panel width/height correction factor is 0.769, shown in Table A8, was extracted from Figure 10 at the intersection of the two red lines, the 251 m wide panel at a depth of 305 m. 2) S,,,x (8.305-ft, shown on Table A8) was calculated as the product of the 12.0-ft mining height times the 0.769 panel width/depth correction factor and the 0.9 virgin ground factor. '• '• 3) The distance from the ribside to the panel center is 412-ft, half of the 825-ft panel width, or 0.412 times the local depth of 1,000-ft. This can be seen by following the blue line downward on Figure 11. 4) The 6-ft partial subsidence is 0.722 times S„~x (a.6-~, =0.722), as shown where the green and red lines intersect on Figure 11. 5) The predicted 204-ft distance inside the northern panel ribside of the 6-ft (0.722 S„~„) partial subsidence to the panel ribside was extracted along the red 0.825 panel width/depth line parallel to the x-axis, as shown on Figure 11. The ribside is located at 0.412 times the depth from the center of Panel #3, where the dashed straight "Ribside" line intersects the red 0.825 panel width depth line. The 6-ft subsidence is 0.208 times the depth where the 0.722 5,,,,, value intersects the red 0.825 panel width depth line. This intersection projects down to the x-axis on the green line at 22.5 of the length between the 0.7 S,~,x and the 0.8 S„~x curved lines. The 0.209 difference between it and the 0.412 times the depth of the "Ribside" is minus 0.209 times the depth (1,000-ft) of the 6-ft (0.722 S„~x value), i.e. 204-ft inside the "ribside". Distances inside the "Ribside" are arbitrarily designated as minus. The maximum tensile (+E) and compressive (-E) horizontal surface strain lines were calculated at each panel subsidence profiling location, using the NCB horizontal strain profiling Graph C4 in Appendix C. The maximum horizontal tensile strain line is the most important because it represents a prediction of the location of ground surface fractures associated with the -27-