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West Elk Mine <br />• water that might be present in this zone has a higher probability of being impacted than that <br />occurring in the centers of the panels. <br />Angle of Maior Influence <br />The angle of major influence, (3, (also called angle of influence of the point of evaluation) is <br />defined by Peng (1992, p. 11) "... as the angle between the horizontal and the line connecting <br />the inflection point and the edge of the radius of major influence." The radius of major influence <br />(r) is therefore the horizontal distance from the vertical projection of the inflection point to the <br />point of maximum subsidence and the limit of subsidence (See Exhibit 60B, Figure 3). The <br />angle of major influence is used for computer modeling by the influence function method. In the <br />B Seam mining at West Elk Mine, the angle of major influence ranges (from a horizontal <br />reference) from about 70 to 80 degrees. For E Seam mining in the South of Divide mining area, <br />the angle of major influence is also expected to range from 70 to 80 degrees, which was used for <br />the computer modeling described below. <br />The angle of major influence may also be referenced to the vertical, as has been done for the <br />break angle and angle of draw. The angle of major influence (from a vertical reference) is <br />roughly equal to the angle of draw, and is therefore predicted to range from 10 to 20 degrees. <br />Relation Between Dynamic and Final Subsidence Deformations <br />Maximum dynamic tilt (change of slope) and horizontal tensile and compressive strain are <br />reportedly less above longwall mining panels than are 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 coal 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 10 ft/day to 40 ft/day; dynamic tilt, therefore, <br />decreased by 14 percent as the face rate of movement increased by 30 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 as the face increased by 30 ft/day. <br />3. Maximum dynamic compressive strain decreased by an averae of 48 percent (0.0062 to <br />0.0032) as the face velocity increased from 10 ft/day to 40' ft/day; dynamic horizontal <br />compressive strain decreased by 16 percent as the face increased by 30 ft/day. <br />Critical Extraction ilv'idih of Tylininz Pastels <br />Critical extraction width (IN) is the width of mining panels -necessary for maximum subsidence to <br />occur at a given overburden depth (d). Values for critical «1/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 50' NW longwall <br />;0 panel, the critical extraction width-to-depth ratio is estimated to be 1.0 in the Apache Rocks and <br />2.05-135 Revised June 2005 PRIG, Rev. Alarch 2006; A4ay 2006 PRI G, Nan. 2006TRI07„4pri12007TR708; Sep. 2007 PR12; Feb. 2008 PR-12