REV93908 - Laserfiche WebLink

Home Browse Search

Sanborn Creek Subsidence Page 21 September 2, 1997 ] B. Maximum individual panel tensile (+E) and compressive (-E) strains were calculated by multiplying Sm,„/depth for each profile l line by the multipliers taken from the prediction graph included in J Appendix B. The subsidence contours plotted on Plate la for panel #1 and on Plate 2a for Panel #2 were predicted from the subsidence profile graph, Figure 5. Figure 6 provides the predicted worst-case horizontal strain profile graph used to locate the maximum strain contours on Plate lb for Panel #1 and for Plate 2b for Panel #2 as a single separate panel. Panel #2 is the first panel to be longwall panel mined in the first group of three panels. ] The vertical subsidence and horizontal strain profile graphs were modified for a 25° angle of draw. It was necessary to make this modification from the NCB subsidence and horizontal strain profile graphs for the NCB 35° angle of draw measured in Great Britain. Appendix B contains the NCB 35 angle of draw profile 1 prediction graphs. Angles of draw measured adjacent to western U.S. coal mines (Pendleton, 1985; Gentry and Abel, 1978; Abel and Lee, 1984) are consistently smaller than the 35° NCB angle of draw. Subsidence contour depths were located along each panel _ ribside and profiles constructed using Figure 5. The following example for the 6-ft subsidence contour at the center of the starter room of 560-ft wide Panel #1, Plate la, demonstrates the calculations at a depth of 500-ft, as follows: 1) Sm„ (8.86-f t, the second line on Table 9) along the subsidence profile occurs at the center of the panel, equidistant from the sides and end of the 560-ft wide Panel #1, i.e. 280-ft inside Panel #1 •' 2) The 6-ft partial subsidence depth represents 0.68 of Sm,x 3) Following the 1.12 panel width/depth ratio (Table 9) of 1.12 profile line from the Y-axis to 0.685^, interpolated between the 0.65, and 0.75, lines on Figure 5 the distance from the panel center to the 6-ft subsidence contour is at 0.42 times the 500-ft depth on the X-axis from the center of the panel (210-ft), or approximately 70-ft inside the panel from the 1 starter room chain pillars. Locations for all the predicted subsidence contour values were calculated and the predicted subsidence contours plotted on Plate la. This process was repeated for Panel #2, Plate 2a to demonstrate the difference between the predicted subsidence for the individual Panel #2 and the predicted subsidence for the initial group of panels; Panel #2 plus Panel #3 and Panel #9. Predicted maximum subsidence over Panel #2 when it is mined and before Panel #3 is mined is 3.90-ft (Table 9). The predicted worst-case subsidence over Panel #2 following mining of Panel #3 and Panel #4 21