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Elk Creek Mine Subsidence Page 37 February 26, 2003 <br />6.1-ft in the 2,600-ft depth area over the Panel #10/Panel #11 <br />gateroad. The Panel Group 2 ultimate maximum predicted surface <br />subsidence contours after interior gateroad pillar failure are <br />plotted on Plate 10. <br />Predicted vertical ground surface subsidence resulting from <br />crushing of gateroad pillars between Panel Group 3 longwall panels <br />ranged from approximately 0.6-ft at the 765-ft depth near Station <br />5-830 where the Panel #17/Panel #16 gateroad passes under Bear <br />Creek to approximately 1.3-ft near Station S-3,000V on the south <br />side of Panel #13 where the Panel #13/Panel #14 gateroad will touch <br />the 2,100-ft overburden contour. The total vertical surface <br />subsidence over the interior gateroads was obtained by adding the-- <br />predicted trough subsidence from each adj°acent"~md"ivi ua panel <br />over the gateroad pillars~to~t~ie p e ted vertical ground surface <br />subsidence resulting from crushing of gateroad pillars. The total <br />predicted maximum subsidence over the interior gateroad pillars <br />ranged from 2.8-ft where Bear Creek crosses over the south side of <br />Panel #16 of the Panel #17/Panel #16 gateroad to 3.9-ft in the <br />2,100-ft depth area over the Panel #13/Panel #14 gateroad. The <br />Panel Group 3 ultimate maximum predicted surface subsidence <br />contours after interior gateroad pillar failure are plotted on <br />Plate 15. <br />The failure of interior gateroad pillars will reduce the <br />predicted horizontal tensile and compressive strains resulting from <br />longwall mining of the individual panels. The magnitude of <br />flexural surface strains are linearly dependent on the maximum <br />downward deflection of the ground surface across the panels. The <br />maximum downward overburden deflection across a single 825-ft wide <br />panel is the calculated maximum subsidence (5,,,,x). Failure of the <br />gateroad pillar will decrease the downward overburden deflection <br />across the panel by the surface subsidence induced by the gateroad <br />failure. For example, in Panel Group 1 at Station N-6,890 in Panel <br />#1 (Table A1), where Bear Creek passes over the north panel ribside <br />at a depth of 350-ft, the maximum vertical panel subsidence is <br />10.8-ft and subsidence from gateroad pillar failure is 0.3-ft. The <br />maximum ground surface subsidence, surface deflection, after <br />gateroad failure would be 10.5-ft. Since no other input factors <br />change, the local maximum tensile strain (+E) on Table 1 will be <br />reduced to: <br />+E _ '0~a e' (20100) = 0.972(20100) = 19500µe <br />The magnitude of the reduction in horizontal surface strains <br />for gateroad pillar failure increases with overburden depth. For <br />example, in Panel Group 3 the maximum subsidence (Sm,x) and <br />deflection across Panel #16 where Bear Creek crosses over the <br />ribside at previously subsided Station 5-925 and at a depth of <br />765-ft is 9.4-ft. The 0.6-ft of surface subsidence over the Panel <br />#17/Panel #17 is 0.6-ft. The local maximum tensile strain (+E) on <br />Table 1 will be reduced to: <br />-37- <br />I <br />• I <br />•~ <br />C <br />C <br />C <br />C <br />C <br />•r <br />l <br />