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4 RAILROAD UNDERMINING <br />The Energy Spur railroad track was undermined by 9 <br />Right Longwall during August of 1996 and by 8 <br />Right Longwall during June and July of 1997. <br />During these two months, Twentymile Coal <br />company again established and then broke the world, <br />monthly, coal production record that had previously <br />been set during the undermining of 9 -Right. The <br />correlation between coal production and track <br />undermining is coincidental and is only noted herein <br />to illustrate the feasibility of mitigation during high <br />rates of production, and hence, high rates of <br />subsidence development. <br />The layout of the railroad relative to each of the <br />longwall panels and the rates of mining progress are <br />illustrated in Figures 6 and 7. Each longwall panel <br />was 840 -ft wide and mined on 1,000 -ft centers. The <br />extracted seam height was 8.5 -ft and the projected <br />rate of retreat was 100 -ft per day. <br />/ <br />TST-4 <br />J <br />ns � <br />dark <br />7 <br />/ <br />/ <br />Ar <br />/ <br />Ar <br />/ j Railroad <br />/ <br />Figure 6 <br />Railroad Subsidence Monitoring Plan <br />a <br />w <br />y � <br />o�J o�J <br />ST -500 <br />