2011-09-23_REPORT - C1980007 (8)

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• • • Subsidence Prediction Based on Measurements Appendix A at West Elk Mine Page 4 the 1NW, 2NW, and 3NW longwall panels at West Elk Mine (Figure C) as summarized in Table 1, Exhibit 60B (included herein). The projected range of maximum vertical displacements, for the South of Divide mining area is shown in Table 2, Exhibit 60B (included herein). South of Divide Mining Area: Overburden depth above the projected E -Seam longwall centers ranges from 400 to 1,425 feet. With a projected longwall panel width of 1,080 feet, and assuming that the chain pillars (gate road pillars) are similar to those in the Apache Rocks mining area, maximum subsidence is predicted as follows: • Panels El to E8: These panels, which will trend roughly N80 °W, will range in width from subcritical to supercritical (width -to depth ratio (W /d) ranges from 0.76 to 2.7). 1. Maximum vertical displacement above the chain pillars (S is expected to range from 0.8 to 2.4 feet (0.1 to 0.3t) where the extraction thickness is 8 feet, 1.2 to 3.6 feet (0.1 to 0.3t), where the extraction thickness is 12 feet, and from 1.4 to 4.2 feet (0.1 to 0.3t), where the extraction thickness is 14 feet. 2. Maximum vertical displacement above the center of the mined panels is projected to range from 4.8 to 6.4 feet (0.6 to 0.8t) where the extraction thickness is 8 feet, from 7.2 to 9.6 feet, where the extraction thickness is 12 feet, and from 8.4 to 11.2 feet (0.6 to 0.8t), where the extraction thickness is 14 feet. • Panel E9: This panel trends about N10 °E and is of supercritical width. 1. Maximum vertical displacement above the chain pillars in this shallow overburden is expected to range from 1.2 feet (0.1 t), where the extraction thickness is 12 feet and from 1.4 feet (0.1t), where the extraction thickness is 14 feet. 2. Maximum subsidence is projected to range from 8.4 to 9.6 feet (0.7 to 0.8t), where extraction thickness is 12 feet, and 9.8 to 11.2 feet (0.7 to 0.8t), where the extraction thickness is 14 feet. Maximum Tilt Maximum tilt (M was calculated from differential vertical displacements at the West Elk Mine monitoring network in terms of the ratio of maximum vertical displacement to overburden depth (S /d in dimensionless units L /L) (Figure D). Tilt values at West Elk Mine range from 1.4 to 2.1 percent. Maximum calculated tilt ranges from about two to three times S /d (2 to 3•(S /d)) at West Elk Mine. Maximum tilt in the South of Divide mining area is projected to range from 2.2 to 2.3 S /d. Maximum tilt in four different mining areas studied by Dunrud (1984, p. 168) in the Western United States ranges from 2.5 to 5•(S /d). South of Divide Mining Area: As stated earlier in this report tilt above the eight longwall panels (panels El to E8) and the single panel (E9) is projected to range between 2.2 and 2.3 S /d for coal extraction thickness ranging between 8 and 14 feet. These values are based on subsidence 831 - 032.690 Wright Water Engineers, Inc.