Laserfiche WebLink
SubTerra, Inc. Sage Creek Mine 11/18/2009 <br />Initial Evaluation of Subsidence Impacts for Continuous Miner Development <br />• 4. 135 to 340 KV power lines. <br />5. 69 KV power lines. <br />Mine Layout <br />Figure 2 shows the planned layout of development entries covered under the current proposal. <br />One thousand foot wide longwall panels will eventually be mined on 1,200 -ft centers using the <br />retreat mining method. Under this mining method, three nominal twenty foot wide development <br />entries will be mined on either side of each panel from the northern end of the mine towards the <br />south. The rigid /yield pillar combination used between each longwall panel will nominally include a <br />series of 120 -ft wide by 220 -ft long rigid pillars each located adjacent to two 40 -ft wide, 100 -ft long <br />yield pillars. <br />The expected extraction ratio during development is less than 30% increasing to greater than 80% <br />during longwall mining. <br />Pre and Post Mining Land Uses <br />The land above the Sage Creek Mine is currently used for farming and will continue to be used for <br />this purpose. County Road 27 and several power lines also cross the area proposed for mining as <br />noted above. <br />• Evaluation of Potential Subsidence Impacts from Room and Pillar Development <br />Potential Subsidence Related Phenomena <br />Measurable subsidence over room and pillar entry development at the extraction ratio and depths <br />proposed for longwall development is unlikely even under the worst conceivable conditions and <br />has, to our knowledge, never been experienced in the project area. <br />Subsidence of the ground surface must be preceded by either failure of the roof above the mine <br />entries and /or failure of the coal pillars by collapse or punching into the floor or roof. Each of these <br />potential failure scenarios is examined below along with the potential effects on subsidence of <br />encountering unexpected faults and water or gas inflows. <br />Roof Failure Potential (Worst Conditions) <br />Peabody Energy has extensive experience designing and installing roof support systems in the <br />Wadge seam based on their experience at the Twentymile mine. Standardized patterned roof bolt. <br />systems analyzed using Niosh's ARBS' (Analysis of Roof Bolts) program indicate an expected <br />Stability Factor of 1.6 (minimum 1.2 recommended). Under worst conditions, the Stability Factor is <br />not estimated to fall below 1.2 leading to the conclusion that the mine roof will be stable until the <br />longwall is mined. Furthermore, while minor roof falls may occur, there is no credible scenario for <br />widespread roof instability in the Wadge seam. <br />' Mark, C., (2000). Design of Roof Bolt Systems. In Mark C, Dolinar DR, Tuchman R, eds. New Technology <br />for Coal Mine Roof Support, Proceedings of the NIOSH Open Industry Briefing, NIOSH IC 9453, pp. 111- <br />• 132. <br />E <br />