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Subsidence Evaluation for the <br />Exhibit 60E South of Divide and Dry Fork Mining Areas Page 11 <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 may 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 />upward) 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 and Dry Fork mining areas, based on the baseline data obtained from subsidence <br />measurements above the 1NW, 2NW, and 3NW longwall panels at West Elk Mine (Figure 4, <br />Table 1). The projected range of maximum vertical displacements, for the South of Divide <br />mining area is shown in Table 2. The projected range of vertical displacements for the Dry Fork <br />mining area is shown on Table 3. <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 />assuming that the chain pillars (gate road pillars) are similar 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 (Table 2): <br />Panels El to E8: These panels trend roughly N80°W, and range in width from subcritical <br />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, S,„= 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 to <br />0.8t), where the extraction thickness is 14 feet. <br />Panel E9: This panel trends about N I OE and is of supercritical width. <br />1. Maximum <br />vertical displacement <br />above <br />the chain pillars in <br />this shallow <br />overburden <br />is expected to range <br />from <br />1.2 feet (0.1t), where <br />the extraction <br />831 - 032.810 Wright Water Engineers, Inc. <br />