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Elk Creek Mine Subsidence Page 28 February 26, 2003 <br />downward flexure and associated extension of the ground surface <br />may open as the result of longwall panel mining. This has <br />historically been referred to as the "break line". Prediction of <br />the maximum horizontal compressive strain line is less important <br />because compression ridges typically represent only a minor <br />hazard. <br />Maximum individual panel tensile (+E) and compressive (-E) <br />microstrains (108e=1µe) were calculated by multiplying the <br />5,,,,x/depth ratio for each profile line by the multipliers taken <br />from the maximum ground surface strain prediction graph, Figure <br />12. for the local panel width/depth factors. The maximum <br />width/depth strain factor graph is included as Graph 2C in <br />Appendix C. The distance of the maximum tensile (+E) and <br />compressive (-E) microstrains are extracted using Graph 4C in <br />Appendix C in the same way as the vertical subsidence distances <br />from the panel ribside using Figure 11 (Graph C3 in Appendix C). <br />For the example case, at the selected Panel #3 location <br />N-3,675V (in virgin ground at a depth of 1,000-ft and 3,675-ft <br />from the east recovery room ribside) on the north side of Panel <br />#3 the strain factor multipliers were extracted from Figure 12, <br />as follows: <br />1) Enter strain factor graph, Figure 12 (Graph B2 in Appendix <br />B), at the 0.825 width/depth ratio on the x-axis and follow <br />the green line up to the intersections with the "EXTENSION" <br />and "COMPRESSION" curves. <br />2) Follow the blue tensile strain line to the y-axis multiplier <br />and read the tensile strain multiplier value of 0.650. <br />3) Follow the red tensile strain line to the y-axis multiplier <br />and read the compressive strain multiplier value of 0.661. <br />4) The maximum tensile microstrain (+E) is calculated as follows: <br />0.650 (Spaxl 0.650(8.3051 <br />+E= oepth = l,oo0 106=5398 µE <br />5) The maximum compressive microstrain (-E) is calculated as <br />follows: <br />0. 661(S~an) 0.66118.305) <br />-E- Depth - 1,000 106=5549 ftE <br />This result is tabulated in Table A7 in Appendix A. <br />-28- <br />