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' Elk Creek Mine Subsidence Page 96 February 26, 2003 CONCLUSIONS • The ground surface over and near the planned "D" Seam longwall ' panels will subside. The surface subsidence will be of the type referred to as trough subsidence. Chimney subsidence in the overburden above the planned Elk Creek Mine longwall panels and ' gateroads will not breach the ground surface. The collapsed immediate roof rock over the longwall panels may penetrate 48-ft upward and the fissured and fractured overburden above the collapsed ' immediate roof may reach up to 126-ft upward. Chimney collapse will not provide a path for water from Bear Creek to enter the Elk Creek Mine. ' The predicted worst-case lowering of the overlying ground surface by trough subsidence accompanying longwall panel mining could be as much as 10.8-ft. The conservative longwall mining induced vertical subsidence predictions for the four Panel Group 1 panels are contoured on Plate 3, for the seven Panel Group 2 panels ' are contoured on Plate 8 and for the eight Panel Group 3 panels are contoured on Plate 8. The panel group subsidence predictions also assume that all longwall panels in the group are instantaneously extracted. The collapsed roof rock accompanying the extraction of ' one panel will provide considerable overburden support before the adjacent panel is extracted and will restrain the cave-side of the gateroad pillars. The expansion of the collapsed roof rock will '~ prevent the maximum possible predicted subsidence assumed from developing if or when the gateroad pillars crush out. ' The maximum predicted horizontal tensile strains at the ground surface will result in open surface fractures roughly along and near the maximum tensile (+E) strain lines on Plate 9 for Panel Group 1, ' on Plate 9 for Panel Group 3 and on Plate 14 for Panel Group 3. The width of these open fractures depend on the maximum ground surface tensile strain developed by the radius of curvature, overburden thickness, of the downward deflecting overburden as the subsidence trough develops over a longwall panel. The surface tensile strain decreases as the radius of curvature increases. The largest predicted tensile strain, 33400µe, is predicted at the depth of ' 210-ft where Bear Creek crosses over the south ribside of Panel #1. Tensile strain of this magnitude will open a large fracture at the ground surface, approximately 2-ft in width. In contrast, the ' predicted 550µe tensile strain where Elk Creek crosses approximately 2,940-ft over the east ribside of Panel #11 will only open hairline fractures, a small fraction of an inch in width. The predicted open ' tensile subsidence fractures that will develop where Bear Creek crosses over some of the planned longwall panels will be roughly perpendicular to the to Bear Creek. The open fractures will channel ' surface water toward Bear Creek from the side slopes. The surface fractures should not divert water from Bear Creek, either downward ~ into the Elk Creek Mine or outward from the Bear Creek drainage. -46-