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. .. <br /> <br />J.E. Stover & Associates -32- May 31, 1996 <br />Bowie No. 2 Mine <br />multiplied by the subsidence correction factor to determine the <br />projected subsidence above the sub-critical panel. In this case <br />the preparer projects a maximum expected vertical subsidence <br />above the sub-critical panel of 0.23 x 5.7 feet = 1.3 feet. <br />The preparer's SEH method application is correct for the case <br />chosen. However, the case chosen is neither the most <br />geotechnically sensitive nor the highest projected subsidence <br />case for the Bowie No. 2 mine plan. As an example an SEH method <br />projection of subsidence was performed above proposed Panel 36. <br />Panel 36 is of particular interest because it occupies a <br />situation roughly analogous to that of the 1st West and 2nd West <br />panels of the Bowie #1, which experienced significant subsidence <br />cracking due to an hypothesized outcrop barrier cantilever <br />failure. Panel 36 is oriented with its long axis parallel to the <br />steep outcrop slope gradient. As such its direction of retreat <br />will be into the slope, which is the preferred orientation <br />beneath a steep slope. The panel is 440 feet wide and <br />approximately 2,100 feet long. Its overburden ranges from <br />slightly less than 300 feet at its southern end to a high of <br />approximately 815 feet about 200 feet south of its northern <br />extremity. As such Panel 36 underlies the steep slope outcrop <br />area of concern for possible poor quality coal burn effects and <br />near surface chimney collapse potential. It also underlies the <br />historically and potentially unstable surface of the steep <br />southern permit area. <br />A rudimentary analysis of the projected maximum vertical <br />subsidence for two points along the long axial centerline of <br />Panel 36 was completed. The first point was chosen to be 0.7 <br />times the panel width from the southern end of the panel. The <br />SEH generally projects maximum subsidence above a sub-critical <br />width panel to be achieved at a distance from the panel end equal <br />or greater than 0.7 times the overburden depth. This condition <br />is first occurs in Panel 36 at a point 280 feet from the southern <br />end of the panel, which coincidentally has an overburden depth of <br />approximately (122 meters) 400 feet (0.7 x 400' = 280'). This <br />point would be susceptible to the development of the maximum <br />projected vertical subsidence after the face had passed a <br />location 1.4 times the overburden depth from the southern end of <br />the panel. Using figures 3 and 4 of the SEH to project the <br />maximum projected subsidence at this point results in a <br />Subsidence Factor, Smax ~ 0.73 (figure 3), and a Subsidence <br />Correction Factor, s/S ~ 0.7 (figure 4). Multiplying these <br />factors times one another and the extracted thickness of 12 feet <br />results in a projected maximum vertical subsidence of 0.73 x 0.7 <br />x 12.0 feet ~ 6.1 feet. This significantly larger than the <br />maximum projected subsidence of 3.5 feet determined by the <br />preparer of Exhibit 15. Further, it is projected to occur <br />