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I Sanborn Creek Subsidence Page 29 September 2, 1997 J Subsidence resulting from crushing was calculated using the method indicated on Figure 7. The only adjustment applied was to change the rock density constant, from 0.0226 MPa/m equivalent to ~~ 144 PCF to 0.0235 MPa/m equivalent to 150 PCF. The following example for the gateroad pillar between Panel #2 and Panel #3 at 2210-ft (674m) of depth explains the method. o.oz3s~e~4~ = 165 MPa (23900 si I - Lmax = 1-0.904 p ) 1 ~ I+maxw = 165( Sp ) = 28.0 Subsidence() = 8.469 + 11.95 In [28.0] = 48.3$ 1 Subsidence(ft) = ioo (8.5) = 4.11-ft (first line,Table 6) 1;: The most conservative possible assumption was made in estimating the impact of gateroad yield pillar crushing induced subsidence. It was assumed that the pillar related subsidence was ! transferred undiminished to the centerlines of adjacent panels. ~' This assumption ignores the arching across Panel #2 from the 1 , unmined B Seam to the east of Panel #2 that will probably support some of the overburden above Panel #2. The same assumption of '• complete transfer of Panel #3/#4 gateroad yield pillar subsidence 1 was applied to Panel #9 centerline. It would probably be more ~ realistic, but less conservative, to assume that only one-half of the subsidence related to gateroad pillar crushing would be transferred to the centerlines of the outside panels in the groups of three panels, i.e. that the vertical subsidence was cantilevered is from the unmined B Seam to the east and the 280-ft wide barrier l pillar to the west. Partial support of the overburden above the J " outside panels would not affect the maximum vertical subsidence over the central panel (Panel #3). However, the maximum horizontal 1 surface strains over the ribsides of the outside panels would decrease significantly because of the linear decrease in the "Local Smax/Depth x 106" factor at the Panel #2 and Panel #9 centerlines. Table 7 presents the incremental and cumulative worst-case vertical subsidence for four east-west cross sections through the `~ initial panel group made up of Panel #2, Panel #3 and Panel #4. The data demonstrates the importance of gateroad pillar crushing to maximum predicted subsidence. Plate 3a graphically presents the worst-case vertical subsidence and Plate 3b the location of the worst-case horizontal strains. Table 8 presents the incremental ,; and cumulative worst-case vertical subsidence for four east-west ~. cross sections through the second panel group made up of Panel #5, I Panel #6 and Panel #7. Plate 4a graphically presents the worst-case vertical subsidence and Plate 4b the location of the worst-case horizontal strains for the second panel group. Table 9 I 29 I