2010-03-05_REVISION - C1996083 (2)

Home Browse Search

17. Maleki Section 4.0 - Mains Orientation and Pillar Designs The stability of near-seam strata was evaluated at the corridorfor the layout illustrated in MTI 2004 Figure 1. An empirical technique developed by NIOSH was used to confirm that the (then- planned) orientation was optimal for stability of the rooms with respect to the horizontal stress field. As stated in 4.1. - Mains Orientation, "the rule of thumb is that the mains should be oriented near parallel to maximum horizontal stress to minimize roof stability problems." The orientation of the mains evaluated for MTI2004 was N 100°E, which was deemed to be favorable because it lay within 20 degrees of the maximum stress orientation (N 90°E). However, the orientation of the mains illustrated on revised Maps 14-B and 27 appears to be N 55° E, which is skewed 35 degrees from the maximum stress orientation. The bearing of the West Mains corridor has been rotated 45 degrees from the layout evaluated in 2004. Please re-evaluate the stability of near-seam strata using the corridor layout now proposed with TR-65. The Division has no further concerns. The Maleki 2010 report in the February 3, 2010 submittal, does not specifically evaluate the stability of near-seam strata using the corridor location proposed with TR-65, but pillar stresses and factors of safety were analyzed (see item 18). 18. An evaluation of pillar stability, using MULSIMTI, is presented in MTI 2004 Section 4.2. Factors of safety ranging from 1.64 to 2.5 were determined for the layout utilized. However, as discussed in the preceding item, the orientation for the mains now proposed with TR-65 differs by 45 degrees from what was evaluated for the MTI 2004 report. Please re-evaluate the anticipated pillar stress levels and factor of safety expected, given the proposed change in orientation of the corridor beneath Terror Creek, and verb that the required factor of safety will continue to be achieved. The Division has no further concerns. Pillar stability for the proposed orientation of the West Mains was evaluated with the February 3, 2010 submittal of the Maleki 2010 report. In addition to the 5-entry West Mains, the model included a rock storage area located adjacent to the southernmost entry. Anticipated factors of safety are shown to be sufficient for the West Mains and rock storage areas. Southeast of these two features is an area that was longwall mined in 2005 and 2006. The factor of safety for the rock storage area would be reduced to 1.4 if retreat mining were to be initiated in the longwall area. An inquiry to Jim Stover, P.E. confirmed that BRL will not be returning to the longwall area to conduct retreat mining operations. 19. Maleki Section 5.0 - Overburden Stability Please provide a statement addressing potential (if any) impact to the anticipated stability of the overburden that may be expected due to the proposed change in orientation of the West Mains. The Division has no further concerns. The Maleki 2010 report in the February 3, 2010 submittal does not specifically address overburden stability using the corridor location proposed with TR-65, but pillar stresses and factors of safety were analyzed (see item 18). General Comments - Mans 20. Map 07 - Geology