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• 1.0 INTRODUCTION <br />This report was prepared as a result of P.O.122193 requesting Maleki Technologies, Inc. <br />(MTI), to assist Bowie Resources, LLC (BRL), for permitting purposes, in a stability <br />evaluation of a proposed set of mains (Third North mains) to be excavated in the Upper B <br />Seam under Hubbard Creek. The focus was on a review of overburden characteristics and <br />an evaluation of pillar stability for long-term support of the overburden. <br />To evaluate rock mass properties above these mains, we have utilized corehole data from <br />two boreholes drilled in the vicinity of the Third North mains (figure 1). At BRL-IP-00- <br />67, BRL partially cored the massive Marine Sandstone horizon (or C Sandstone) (figure <br />2). In addition, near-seam strata conditions were examined at DD-D9X43-37 by <br />reviewing the D to B cored interval, including the immediate roof and floor of both the <br />Upper and Lower B seams. This corehole was drilled from the Upper D Seam workings <br />toward the B Seam and provided critical data about the strength of the coal seams and <br />roof/floor strata. <br />r? <br />?J <br />Because pillar stability is important for controlling overburden deformation, pillar stress <br />and factors of safety were calculated for the Hubbard Creek mains while the influence of <br />overlying workings in the Upper D Seam and neighboring works in the historic U.S. Steel <br />mine were modeled (figure 1). Pillar strength was estimated using a method developed <br />by researchers at the National Institute for Occupational Safety and Health (NIOSH). <br />Pillar stress was calculated using a pseudo-three-dimensional boundary-element <br />technique that accounts for variability in the overburden realistically. <br />Conclusions are presented in section 2. The geotechnical framework for BRL properties <br />is reviewed in section 3. This section also includes an evaluation of the stress field and <br />representation of rock mass quality for select overburden stratigraphic units. Because of <br />variations in the overburden and multiple-seam geometries, a boundary-element model <br />was used to calculate pillar stresses and factors-of-safety (section 4). <br /> <br />Maleki Technologies, Inc. Page 2