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Subsidence Evaluatron For <br />Exhibit 608 South of Divide Mining Area Page 8 <br />• <br />In flat or gently sloping terrain, vertical displacement typically increases inward from the limit of <br />the subsidence depression, is half the maximum value at the point of inflection, and is maximum <br />in the middle of the depression (also called subsidence basin or subsidence trough). Horizontal <br />displacement and tilt increase inward from the margin of the depression to a maximum at the <br />point of inflection and become zero again at the point of maximum vertical displacement <br />(Figure 3). Maximum values of tilt, curvature, and strain, discussed herein, apply only to slopes <br />less than about 30 percent; values tray be greater on slopes steeper than 30 percent. <br />Positive curvature (convex upward) and horizontal tensile strain increase inward from the margin <br />of the depression to a maximum about midway between the depression margin and the point of <br />inflection and decrease to zero again at the point of inflection. Negative curvature (concave <br />upwazd) and compressive horizontal strain increase inward from the point of inflection to a <br />maximum about midway between the point of inflection and the point of maximum vertical <br />displacement and decrease to zero again at the point of maximum vertical displacement <br />5.3.1.1 Maximum Vertical Displacement (Subsidence) <br />The following range of vertical displacements (subsidence values) are projected for the South of <br />Divide mining area, based on the baseline data obtained from subsidence measurements above <br />the 1NW, 2NW, and 3NW longwall panels at West Elk Mine (Figure 4, Table 1). The projected <br />range of maximum vertical displacements, for the South of Divide mining area is shown in <br />Table 2. <br />• South of Divide Mining Area: Overburden depth above the projected E Seam longwall centers <br />ranges from 400 to 1,425 feet With a projected longwall panel width of 1,080 feet, and <br />assLming that the chain pillars (gate road pillars) are similaz to those in longwall panel 17 of the <br />Apache Rocks mining area, maximum subsidence (vertical displacement Sm= a • t) is predicted <br />as follows (1"able 2): <br />Panels EI to E8: These panels, which will trend roughly N80°W, will range in width <br />from subcritical to supercritical (width-to depth ratio (W/d) ranges from 0.76 to 2.7). <br />1. Maximum vertical displacement above the chain pillars (S~) is expected to range <br />from 0.8 to 2.4 feet (0.1 to 0.3t) where the extraction thickness is 8 feet, 1.2 to 3.6 <br />feet (0.1 to 0.3t), where the extraction thickness is 12 feet, and from 1.4 to 4.2 feet <br />(0.1 to 0.3t), where the extraction thickness is 14 feet <br />2. Maximum vertical displacement (subsidence, Sm= a • t) is projected to range from <br />4.8 to 6.4 feet (0.6 to 0.8t) where the extraction thickness is 8 feet, from 7.2 to 9.6 <br />feet, where the extraction thickness is 12 feet, and from 8.4 to 11.2 feet (0.6 tq <br />0.8t), where the extraction thickness is 14 feet <br />• Panel E9: This panel trends about N 10°E and is of supercritical width <br />1. Maximum vertical displacement above the chain pillars in this shallow <br />• overburden is expected to range from 12 feet (O.lt), where the extraction <br />831-032.690 Wright WaterFsgineers, Inc_ <br />