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Sanborn Creek Subsidence Page 29 September 2, 1997 <br />Subsidence resulting from crushing was calculated using the <br />• method indicated on Figure 7. The only adjustment applied was to <br />change the rock density constant, from 0.0226 MPa/m equivalent to <br />144 PCF to 0.0235 MPa/m equivalent to 150 PCF. The following <br />example for the gateroad pillar between Panel #2 and Panel #3 at <br />2210-ft (674m) of depth explains the method. <br />Lmax = o. oz3s(s~sl = 165 MPa (23900 si) <br />i-o.soa p <br />l+max ~"-, = 165 ( Sos) = 28.0 <br />Subsidence() = 8.469 + 11.95 In [28.0] = 48.38 <br />Subsidence(ft) = io'o (8.5) = 4.11-ft (first line, Table 6) <br />The most conservative possible assumption was made in <br />estimating the impact of gateroad yield pillar crushing induced <br />subsidence. It was assumed that the pillar related subsidence was <br />transferred undiminished to the centerlines of adjacent panels. <br />'' This assumption ignores the arching across Panel #2 from the <br />unmined B Seam to the east of Panel #2 that will probably support <br />some of the overburden above Panel #2. The same assumption of <br />'• complete transfer of Panel #3/#4 gateroad yield pillar subsidence <br />was applied to Panel #4 centerline. It would probably be more <br />realistic, but less conservative, to assume that only one-half of <br />the subsidence related to gateroad pillar crushing would be <br />transferred to the centerlines of the outside panels in the groups <br />of three panels, i.e. that the vertical subsidence was cantilevered <br />from the unmined B Seam to the east and the 280-ft wide barrier <br />pillar to the west. Partial support of the overburden above the <br />outside panels would not affect the maximum vertical subsidence <br />over the central panel (Panel #3). However, the maximum horizontal <br />surface strains over the ribsides of the outside panels would <br />decrease significantly because of the linear decrease in the "Local <br />Smaa/Depth x 106" factor at the Panel #2 and Panel #4 centerlines. <br />Table 7 presents the incremental and cumulative worst-case <br />vertical subsidence for four east-west cross sections through the <br />initial panel group made up of Panel #2, Panel #3 and Panel #4. <br />The data demonstrates the importance of gateroad pillar crushing to <br />maximum predicted subsidence. Plate 3a graphically presents the <br />worst-case vertical subsidence and Plate 3b the location of the <br />worst-case horizontal strains. Table 8 presents the incremental <br />and cumulative worst-case vertical subsidence for four east-west <br />cross sections through the second panel group made up of Panel #5, <br />Panel #6 and Panel #7. Plate 9a graphically presents the <br />worst-case vertical subsidence and Plate 9b the location of the <br />worst-case horizontal strains for the second panel group. Table 9 <br />• <br />29 <br />