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YVest Elk Mane <br />2. The third panel southward will be suberitical beneath Box Canyon based on width-to-depth <br />• ratios [W/d] ranging from 0.5 to 1.1. Maximum subsidence is projected to range from as much <br />as 8.4 feet (0.7t) in azeas of shallower overburden to about 6.0 feet (O.St) under deepest cover, <br />S~ is projected to range from 2.4 feet (0.2t) to as much as 4.8 feet (0.4t) in areas of deepest <br />cover. <br />3. Panels 4 through 6 range from about critical to subcritical (W/d = 1.3 to 0.5), assuming that the <br />chain pillars support the overburden load. However, maximum subsidence is expected to range <br />from 3.6 to 7.2 feet {0.3t to 0.6t) because the subsidence factor above the chain pillars (S~) is <br />projected [o range from 3.6 to 7.2 feet (0.3t to as much as 0.6t). Subsidence of as much as 7.2 <br />feet (0.6t) is therefore projected because the chain pillars and caved material in the caved zone <br />(gob) are projected to compress about equally. With the increased overburden loads under West <br />Flatiron and its flanking cliffs and steep slopes, these three southern panels are expected to <br />locally subside as a super panel (i.e., multiple panels and adjacent chain pillars that behave as a <br />single panel) of supercritical width beneath areas of greatest overburden depth. <br />4. The subsidence factor is projected to be less where the B-Seam roof rocks (sandstones, shales, <br />and siltstones) cave into dry mining conditions than it will be where the roof rocks cave into wet <br />mining conditions. This variance is expected because the fmal bulking factor of caved rocks <br />under dry conditions is greater than it is for caved rocks under wet conditions. <br />South of Divide Mining Area - <br />• The following range of vertical displacements (subsidence values) are projected for the <br />South of Divide mining area based on the baseline data obtained from subsidence <br />measurements above the 1NW, 2NW, and 3NW longwall panels at West Elk Mine (see <br />Figure 3 and Table 1, Exhibit 60B) and the proposed E Seam mining configuration (Map <br />51). The projected range of maximum vertical displacements, for the South of Divide <br />mining area is shown in Table 2 of Exhibit 60B. <br />Overburden depth to the E Seam above the projected longwall centers within the South of <br />Divide mining area ranges from 400 to 1,425 feet. With a projected longwall panel width of <br />1,080 feet, and assuming that the chain pillars (gate road pillars) are similar to those in <br />longwall Panel 17 of the Apache Rocks Mining Area, maximum subsidence (vertical <br />displacement - Sm=at) is predicted as follows (Table 2 of Exhibit 60B): <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 (Scp) is expected to <br />range from 0.8 to 2.4 feet (0.1 to 0.3t) where the extraction thickness is 8 feet, 1.2 <br />to 3.6 feet (0.1 to 0.3t), where the extraction thickness is 12 feet, and from 1.4 to <br />4.2 feet (0.1 to 0.3t), where the extraction thickness is 14 feet. <br />2. Maximum vertical displacement (subsidence, Sm=at) is projected to range from <br />. 4.8 to 6.4 feet (0.6 to O.St) where the extraction thickness is 8 feet, from 7.2 to 9.6 <br />2.05-1 /5 Revised November 2004 PRIO <br />