PERMFILE47424 - Laserfiche WebLink

Home Browse Search

5.2.2 Seam Interaction and Cascading Pillar Failure Anah~sis Seam interaction between the Sage Creek and Wolf Creek Seams in Seneca IIW • was analyzed in conjunction with another issue that affects web and barrier pillar desien- that of cascading pillar failure (CPF). CPF`s can occur when failure in one pillar results in stress transfer to adjacent pillars. which, in tum, fail. In their mildest form (slow pillar squeezes), this failure may take weeks to proeress. In their most severe form, failures can occur almost instantaneously, resultine in severe air blasts, damaee to equipment, and loss of life. To check the performance of the web pillar designs in each seam against CPF, including the Sage Creek/\Volf Creek interaction, additional LAMODEL analyses were run. In these models. failure of a web pillar was simulated to see if the remaining pillars had a tendency for cascading pillar failure. or if they could absorb the additional load from the failed pillar. Results are presented in Figures 40 through 47. In Figure 40a, failure is simulated by removing an entire web pillar from the Wadge Seam, Seneca IIW. This causes the adjacent web pillars to take additions] load, although not to the point that they yield. This stress transfer dissipates in the adjacent pillazs, indicating that the design is not prone to CPF. Associated safety factors are shown in Figure 40b. Very similaz results for single seam mining of the Wolf Creek in Seneca IIW and of the Wadge and \Vo]f Creek seams in the Yoast area are shown in Figures 41 through 43. In the multiple-seam setting of the Seneca IIW Area. failure of one pillaz in the Sage Creek (Figures 44a and 44b) does not cause CPF, and does not cause instability in • the underlying Wolf Creek Seam (Figures 45a and 45b). Failure of a pillar in the Wolf Creek (Figures 46a and 46b) does not lead to CPF, nor does it significantly affect the overlying Sage Creek Seam (Figures 47a and 47b). The models presented in Figures 40 through 47 support the conclusion that the web pillar designs are not prone to CPF. The issue of cutting off centers (and therefore ]eavin~ an inadequate web pillar between the current and preceding opening) was not explicitly analyzed. but this condition would be less severe than the pillar failure scenarios modeled. since for every pillar whose width is reduced. the width of the next pillar is doubled (assuming the next entry is aligned properly). The risk of cutting off centers lies not in pane] instability. but in miner burial. Local yielding of the web pillar as it is thinned by miner misalignment can lead to roof instability. ]f the miner actually cuts into the adjacent opening, the roof span doubles, and ii is likely that this doubled span ~a~ould not remain stable for long. Opening alignment should be helped by the seam crossdips. They should make the miner tend to wander in the same direction. as opposed to the random misalignment that would occur in a flat seam. 5.3 UDEC Analysis Because LAMODEL onh~ computes in-seam stresses. an additional modeling analysis using UDEC (Universal Distinct Element Code) was performed to confirm the • Seneca Coal Compam 1 8 NSA En~ineerine- in<. Hi=_hu•al1 Mine Design Repon ]one ?007