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Elk Creek Mine Subsidence Page 1 <br />February 26, 2003 <br />EXECUTI~/E SUMMARY <br />' • The Elk Creek Mine will mine nineteen variable length longwall <br />panels in the "D" Seam which will be mined sequentially, indicated <br />on Figure 1. Panel #12 is the shortest at approximately 3,160-ft <br />' in length and Panel #16 is the longest at approximately 8,790-ft. <br />The panels will extract a 785-ft wide coal block which will result <br />in an 825-ft open width between the gateroad pillars across the <br />gateroad entry on each side of the coal block. The panels are <br />' separated into three panel groups by barrier pillars that range <br />from 200-ft to 500-ft in width alongside each panel group. Panels <br />#1 through #4 on Figure 1 constitute Panel Group 1, Panels #5 <br />' through #11 Panel Group 2 and Panels #5 through #11 Panel Group 3. <br />The thickness of the overburden overlying the "D" Seam panels <br />ranges from 210-ft where the south side of Panel #1 will cross <br />' under the Bear Creek drainage to 2,800-ft over the gateroad between <br />Panel #10 and Panel #11. <br />' Two types of subsidence can develop above underground coal <br />mine workings, chimney and trough. The thickness of the overburden <br />between the "D" Seam and the ground surface, shown by the contours <br />' on Figure 1, will prevent the extremely permeable chimney collapse <br />rubble from breaching the ground surface anywhere above the Elk <br />Creek Mine. The minimum 210 feet of overburden over the 12-ft high <br />longwall Panel #1 or adjacent maximum 9,5-ft high gateroad entries <br />' • will not be penetrated by worst-case conical chimney collapse, as <br />indicated on Figure 2. Theoretically, maximum conical collapse <br />chimney height should not exceed 120-ft above the roof of longwall <br />a panels and 95-ft above the roof of gateroad entries and crosscuts. <br />These maximum conical chimney collapse heights are ten times the <br />mining height, because the typical greater than 30~ swell of the <br />broken collapsed Coal measure rock rubble will completely fill and <br />plug further conical chimney collapse (Piggott and Eynon, 1977). <br />' Conical chimney collapse can develop above entry and crosscut <br />intersections, as shown on Figure 2, where collapsed roof rock can <br />move outward into intersecting entries and crosscuts. Rectangular <br />' collapse typically develops above the longwall panels, where the <br />collapse rubble is confined between panel ribsides, as indicated on <br />Figures 2, 3 and 4. Theoretically, rectangular chimney collapse <br />' will only penetrate 36-ft upward into the immediate roof. Kenny <br />(1969) reported the height of waste caving over actual English <br />longwalls as approaching four seam mining heights. This would <br />amount to 48-ft above the maximum 12-ft high longwall panels. <br />1 More permeable fractured and fissured tensilly strained rock <br />extends upward above rectangular chimney collapse longwall rubble, <br />' as indicated on Figures 3 and 9. Kratzsch (1983) indicated (Figure <br />5) that fracturing and fissuring develops above rectangular chimney <br />collapse because of extension that develops as the overburden <br />deflects downward during trough subsidence. Schulte (1957) <br />reported that fractured and fissured rock extended nine times the <br />-1- <br />