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Subsidence Evaluation For <br />Exhibit 60 The Apache Rocks And The Box Canyon Mining Areas Page 15 <br />• modeling by the influence function method. In the current West Elk mining area, the angle of <br />major influence ranges from about 18 to 20 degrees. <br />4.7 Reported Relations Between Dynamic and Final Subsidence Deformations <br />Maximum dynamic tilt (change of slope) and horizontal tensile and compressive strain are <br />commonly less above longwall mining panels than aze the final tilt and strain values at panel <br />boundaries. Dynamic tilt and strain decrease, relative to final tilt and strain, as the rate of face <br />advance increases. <br />Dynamic tilt and strain reportedly decrease with increasing speed of longwall coat extraction <br />(Peng 1992, p. 20-21). Based on observations in a West Virginia coal mine: <br />1. Maximum dynamic tilt decreased by an average of 42 percent (from 0.0024 to 0.0014) as the <br />mining face rate of movement increased from IO fUday to 40 ft/day; dynamic tilt therefore <br />decreased by 14 percent as the face rate of movement increased by l0 ft/day. <br />2. Maximum dynamic tensile strain decreased by an average of 22.5 percent (from 0.0031 to <br />0.0024) as the mining face velocity increased from 10 ft/day to 40 ft/ day; dynamic horizontal <br />tensile strain decreased by 7.5 percent for a face velocity increase of 10 ft/day. <br />• 3. Maximum dynamic compressive strain decreased by an average of 48 percent (0.0062 to <br />0.0032) as the face velocity increased from 10 ft/day to 40 fUday; dynamic horizontal <br />compressive strain decreased by 16 percent for a face velocity increase of 10 fr/day. <br />4.8 Critical Extraction Width of Mining Panels <br />Critical extraction width (W~,) is the width of mining panels necessary for maximum subsidence <br />to occur at a given overburden depth (d). Values for W~~d typically range from about 1.0 to 1.4, <br />with an average of about 1.2. Based on the subsidence development data for the 5th NW <br />longwall panel, the critical extraction width may be closer to the average value of l.2 than l.4 in <br />the Apache Rocks and the Box Canyon mining azeas (see Figure 8 and Section 5.0 for details). <br />4.9 Results of Computer Modeling <br />A computer softwaze package was used to model the results of subsidence measurements at the <br />West Elk Mine and to project subsidence amounts in the Apache Rocks and Box Canyon mining <br />azeas. The package used is entitled: "Comprehensive and Integrated Subsidence Prediction <br />Model (CISPIvf)," Version 2.0, by Syd S. Peng and Yi Luo, Department of Mining Engineering, <br />College of Ivtineral and Energy Resources, West Virginia University. Ivtorgantown, West <br />Virginia. This program performed an influence function analysis and best fit of the West Elk <br />Mine subsidence data. The fit between the data points and the influence function output from the <br />• <br />831-032.181 Wright Water Engineers, Inc. <br />