Laserfiche WebLink
' h ' <br />Seneca Coal Company <br />MSHA I.D. OS-00304 <br />Highwall Mining Addendum <br />March 15, 2004 <br />• Geotechnical Design and Operational Considerations for <br />Highwall Mining, Seneca IIW and Yoast Areas, <br />Seneca Mine <br />EXECUTIVE SUMMARY <br />At the request of Mr. John Rusnak; Director Geology, Peabody Energy, NSA Engineering, <br />Inc., performed evaluations of the geotechnical design requirements and related operational <br />considerations for highwall mining at the Seneca Mine neaz Hayden, CO. Highwall mining with a <br />Peabody Energy-owned Superior Highwall Miner (PM) will be conducted, with potential <br />penetration up to 1,000 ft into the highwall. Two different areas were analyzed: the Seneca IIW <br />Area, and the Yoast Area. Within the Seneca ITW azea, three seams will be targeted. From the <br />lowest elevation upward, they are the Wolf Creek, Sage Creek, and Wadge Seams. In the Yoasf <br />azea, only the Wolf Creek and Wadge Seams aze targeted. <br />This report addresses the following specific issues relative to highwall mining with the <br />Superior Highwall Miner (SHM) at the Seneca Mine: <br />• What specific geotechnical/geological constraints exist within the identified coal <br />seams and mining areas that may limit highwall mining applications? <br />• • For each seam to be mined, what minimum web pillar dimension (as a function of <br />depth, mining height, and material properties) will ensure that highwall stability is <br />unaffected by mining operations? <br />• What is the potential for "cascading pillar failure," and if required, what minimum <br />dimension of barrier pillar will be required to sufficiently isolate extraction panels <br />within and between major mining regions along the existing highwall? <br />• For each coal seam, what is the potential for out-of-seam dilution of the mined <br />product, taking into account roof stability for 11.5-ft-wide rectangular openings and <br />anticipated roof/floor conditions? <br />• Where the Wolf Creek and Sage Creek Seams are mined in close proximity, to what <br />degree will seam interaction dictate special operational or design considerations? <br />• What operational measures can be taken to increase highwall mining efficiency and <br />safety? <br />To best address these questions, NSA's evaluation was conducted by completing three <br />Tasks, including (1) site characterization (review of site conditions and current highwall <br />stability, core recovered from the Yoast Area, physical property testing, etc.); (2) engineering <br />• design (empirical and numerical modeling evaluation of optimal mining plans for the Seneca IIW <br />and Yoast Areas); and (3) operational considerations (identification of relative risks to mining <br />by pit, production efficiency, potential for out-of--seam product dilution etc.). <br />l0 <br />