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C-1996-083 TR-65 <br />MLT Adequacy Review <br />08-Jan-2010 <br />Page 2 of 3 <br />Maleki Section 3.0 - Geotechnical Framework <br />Section 3.1 describes the geologic setting of the Somerset Coal Field and the Bowie No. <br />2 Mine. The "West Mains fault" is addressed at the bottom of Page 9, but does not <br />appear on Figure 1 of Maleki. A faint, dashed line does appear on revised Map 27 (and <br />on PAP Map 07 - Geology) in the approximate location described by Maleki. Map 08 <br />(Geologic Cross Section) of the PAP clearly illustrates the interpreted magnitude of the <br />fault, and implies a near-vertical plane. Due to the potential significance of this feature, <br />its existence should be clearly indicated on each Map for which the fault may be <br />pertinent. <br />At a minimum, please modify Maps 07,14-B and 27 to clearly portray the location of <br />what the Division understands to be the "West Mains fault": For Map 07, it may be <br />more accurate to illustrate the location on the surface, if known,rather than at the B- <br />oo D-seam depth. <br />Maleki Section 4.0 - Mains Orientation and Pillar Designns <br />The stability of near-seam strata was evaluated at the corridor for the layout illustrated in <br />Maleki Figure 1. An empirical technique developed by NIOSH was used to confirm that <br />the (then-planned) orientation was optimal for stability of the rooms with respect to the <br />horizontal stress field. As stated in 4.1 - Mains Orientation, "the rule of thumb is that the <br />mains should be oriented near parallel to maximum horizontal stress to minimize roof <br />stability problems." The orientation of the mains evaluated by Maleki was N 100° E, <br />which was deemed to be favorable because it lay within 20 degrees of the maximum <br />stress orientation (N 90° E). However, the orientation of the mains illustrated on revised <br />Maps 14-B and 27 appears to be N 55° E, which is skewed 35 degrees from the <br />maximum stress orientation. <br />The bearing of the West Mains corridor has been rotated 45 degrees from the layout <br />evaluated in 2004. Please re-evaluate the stability of near-seam strata using the <br />corridor layout now proposed with TR-65. <br />An evaluation of pillar stability, using MULSIMTI, is presented in Section 4.2. Factors <br />of safety ranging from 1.64 to 2.5 were determined for the layout utilized. However, as <br />discussed in the preceding item, the orientation for the mains now proposed with TR-65 <br />differs by 45 degrees from what was evaluated for the Maleki report. <br />Please re-evaluate the anticipated pillar stress levels and factor of safety expected, <br />given the proposed change in orientation of the corridor beneath Terror Creek, and <br />verify that the required factor of safety will continue to be achieved.