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OVERBURDEN STABILITY EVALUATION <br />AT TERROR CREEK CROSSING <br />1.0 INTRODUCTION <br />This report was prepared as a result of P.O.252876 requesting Maleki Technologies, Inc. (MTI), <br />to assist Bowie Resources, LLC (BRL), in reassessment of pillar stability for a new layout <br />developed by BRL for a set of mains in the Upper B Seam under Terror Creek for permitting <br />purposes. The work was completed in several phases. Phase 1 encompassed the design of a <br />geotechnical data gathering plan and training of field personnel during data collection (MTI <br />2003) followed by more detailed stability evaluation of the overburden, above a 5-entry main <br />crossing under Terror Creek (MTI 2004). The specific objective of this phase is to briefly review <br />pillar stability for the new layout using the experience gained during development and extraction <br />of the neighboring longwall block. <br />C <br />Figure la presents the mining geometry including a set of 5-entry mains and a rock storage panel <br />intended for storing excavated rock from the construction of a shaft. While the mains need to • <br />remain stable for the life of the mine, the storage panel has limited life and will be backfilled <br />with rock shortly after its development. Shown also in Figure la is the location of three <br />geotechnical coreholes drilled by BRL to characterize hydrogeologic and rock mass properties <br />near these mains (MTI 2004). These holes were continuously cored below the bed rock and <br />logged for lithology and structure and provided the core for site specific mechanical property <br />testing. The graph on the report cover shows typical geologic conditions (Hunt 2004). <br />Geophysical logs of electrical resistivity, radiation (both gamma ray and gamma-gamma <br />density), caliper, temperature and sonic properties were also obtained for each hole. <br />Both empirical and analytical techniques were used to assess pillar stability, required for limiting <br />overburden displacements within elastic limits. An empirical technique developed by National <br />Institute for Occupational Health and Safety (NIOSH) was used to estimate in-situ strength of <br />coal pillars. Because pillar stability is important for controlling overburden deformation, factors <br />of safety were calculated for individual pillars by dividing pillar strength by stress. Pillar stress <br />was calculated using a pseudo-three-dimensional boundary element technique that accounts for <br />C <br />Maleki Technologies, Inc. Page 2