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1 Sanborn Creek Subsidence Page 1 September 2, 1997 <br />1 EXECUTIVE SUMMARY <br />Plates 1 through Plates 6 present worst-case predictions of <br />vertical surface subsidence and the maximum tensile and compressive <br />strain locations for planned Sanborn Creek Mine B Seam longwall <br />mining. The scale of these worst-case subsidence prediction plans <br />is 1-in equals 500-ft, the same as the enclosed mine map. The <br />predicted vertical subsidence will probably exceed the actual <br />vertical subsidence by approximately one-third because of various <br />J conservative assumptions applied. <br />J Trough subsidence above and adjacent to the planned Sanborn <br />Creek Mine B Seam longwall panels is the only type of subsidence <br />that will affect either the ground surface or mine workings in the <br />overlying D Seam, Oliver No. 1 Mine, or in the overlying E Seam, <br />Hawksnest Mine, shown on the drawings in Appendix A. Chimney <br />subsidence is unlikely to develop over the longwall panels or <br />adjacent supported gateroads, but if it does is extremely unlikely <br />to progress upward to the D Seam, approximately 238-ft overhead. <br />Maximum trough subsidence at the surface overlying and adjacent to <br />the planned longwall panels in the B Seam, shown on Figure 1, will <br />result from longwall mining groups of three adjacent longwall <br />panels and from crushing of the gateroad pillars between the <br />panels. Maximum subsidence will occur when the third panel is <br />mined to completion at the time the last of the gateroad yield <br />1 pillars between the second and third longwall panels in the group <br />_ of three panels crush under the loads arched from over those two <br />immediately adjacent mined out panels. Subsidence extending over <br />one group of three longwall panels from mining the adjacent groups <br />_ of three longwall panels will be minimal because panel groups will <br />be isolated by approximately 280-ft wide barrier pillars. <br />Individual panel depths range from a maximum of 2520-ft at the <br />' starter room, north end of Panel #10, to 690-ft at the equipment <br />recovery room, south end of Panel #8. Planned width of panel <br />groups range from 1720-ft (Panels #11 - #13) to 2000-ft (Panels #5 <br />- #6) . <br />1 Maximum, worst-case , trough subsidence effects were <br />conservatively predicted. The predictions may be approached but <br />will not be exceeded. Predicted maximum vertical subsidence ranges <br />from 9.03-ft (Panels #5 - #6) to 11.63-ft (Panels #11 - #13). <br />Predicted maximum horizontal tensile strains at the ground surface <br />range from 5660µe (Panels #2 - #9) to 9080µe (Panels #11 - #13). <br />1 Tensile strains on the order of 9000µe will result in open <br />_1 fractures approaching 1-ft in width at the ground surface, a <br />relatively short distance outside the horizontal limits of each <br />1 individual panel group. Predicted maximum horizontal compressive <br />_ strains range from 10960µe (Panels #5 - #7) to 15060µe (Panels #11 <br />- #13). Compressive strains of the magnitude of 15000µe will <br />result in compression ridges being thrust up at the ground surface <br />1 <br />