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Geotechnical Design and Operational Considerations <br />for High\\'all Mining, Seneca IIW and Yoast Areas <br />Seneca Mine <br />1.0 INTRODUCTION <br />At the request of 1`9r. John Rusnak, Director Geology, Peabody Energy, NSA <br />Engineering, Inc., performed evaluations of the eeotechnical design requirements and <br />related operational considerations for highwall mining at the Seneca Mine near Hayden, <br />CO. Highwall mining with a Peabody Energy-owned Superior Highwall Miner (PM) <br />will be conducted; with potential penetration up to ],000 ft into the highwall. Two <br />different azeas were analyzed: the Seneca lIW Area, and the Yoast Area (Figure 1). <br />Within the Seneca lIW area, three seams will be targeted. From the lowest elevation <br />upward, they are the Wolf Creek, Sage Creek. and Wadge Seams. In the Yoast area, only <br />the Wolf Creek and Wadge Seams are tazgeted. The Wolf Creek Seam vazies in <br />thickness from 6 to 25 ft, the Wadge Seam varies from 7 to 15 ft, and the Sage Creek <br />Seam is a consistent 5 ft over most of the reserve area. In the Seneca IIW Area, seam <br />interaction between the Sage Creek and Wolf Creek seams is possible. as the interburden <br />ranges from 0 to ] 20 ft. After examining the seam model, it appears unlikely that seam <br />interaction between other seams wil) be a factor in highwall mining. <br />This report addresses the following specific issues relative to highwall mining • <br />with the Superior Highwall Miner (SHM) at the Seneca Mine: <br />• \\'hat specific geotechnicaUgeological constraints exist within the identified coal <br />seams and mining areas that may limit high.+•all mining applications? <br />• For each seam to be mined, what minimum .+eb pillar dimension (as a function <br />of depth, mining height, and material properties) will ensure that high.+~al1 <br />stability is unaffected by mining operations? <br />• \\'hat is the potential for "cascading pillar failure,'' and if required, what <br />minimum dimension of barrier pillar rj ill be required to sufficiently isolate <br />extraction panels within and between major mining regions along the existing <br />high~i~all? <br />• For each coal seam, ~;hat is the potential f'or out-of-seam dilution of the mined <br />product, taking into account roof stability for 17.S-ft-ride rectangular openings <br />and anticipated rooUfloor conditions? <br />• \\'here the \\'olf Creek and Sage Creek Seams are mined in close proximity, to <br />what degree will seam interaction dictate special operational or design <br />considerations? • <br />Seneca Coal Company l NSA Engineering, ]nc. <br />Highwall Aline Design Fepon June 2003 <br />