2008-03-21_PERMIT FILE - C1980007A (8)

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• Panel E9: Maximum tilt in this panel is predicted to range from 0.034 to 0.044 (3.4 and 4.4 percent), where 12 feet of coal is mined and from 0.039 to 0.052 (3.9 to 5.2 percent) where 14 feet of coal is produced. Dry Fork Mining Area: Tilt above the five longwall panels (panels E2 to E6) extending into the Dry Fork mining area is projected to range between 2.2 and 2.3 Sm/d for coal extraction thickness ranging between 9 and 10 feet. These values are based on subsidence measurements at West Elk Mine (Table 1, Figure 5). The overburden depth above the longwall panel centers ranges from 800 to 1,400 feet (Table 3). • Panels E2 to E6: Maximum tilt in these panels is projected to range from 0.011 to 0.0140 (1.1 to 1.4 percent) where 9 feet of coal is extracted and from 0.01 to 0.019 (1.0 to 1.9 percent) where 10 feet of coal is mined. 5.3.1.3 Maximum Horizontal Strain Maximum positive horizontal strain (Em) measured at the West Elk Mine monitoring network ranges between 1.1 and 1.4 times (Sm/d) (or 0.0058 and 0.0102-that is 0.58 and 1.0 percent); maximum negative strain between -0.20 and -4.0 times (Sm/d) (or 0.0009 and 0.0307-0.09 to 3.0 percent) (Table 1). The range of horizontal tensile strain in four different mine areas of the Western United States studied by Dunrud is 0.45 to 3 (Sm/d). The curves projected for tensile and compressive strain in the South of Divide mining area, based on the West Elk Monitoring Network and the National Coal Board of the United Kingdom, are shown in Figure 5. Maximum tensile and compressive strain is significantly greater above large barrier pillars and rigid chain pillars and mine boundaries than it is above longwall mining faces. This is because tensile strains caused by mining the two adjacent panels are additive above the common rigid chain pillars or unyielding mine panel boundary pillars. Cracks tend to be wider and deeper rigidity (for example, the large tension crack on the north side of Lone Pine Gulch). The tensile strains obtained from the curves in Figure 5 are believed to be conservative for the South of Divide and Dry Fork mining areas. Maximum horizontal tensile strains, measured by Dunrud (2006, p. 10) in bedrock during annual observations in the Apache Rocks area (in hard brittle sandstone, where the only strain is revealed by cracks), were 0.0031 to 0.0062 (0.31 to 0.62 percent). These values are about 35 to 45 percent less than those shown in Table 1. The tensile strain is considered to be close to a maximum value for those observed by Dunrud in the Apache rocks area because 1) the features are located above the area if influence of a large solid coal pillar, and 2) no greater strain was observed in the Apache Rocks mining area. South of Divide Mining Area: Maximum tensile and compressive horizontal strains are calculated, using the values obtained from the West Elk Mine area, and as projected in Figure 5 (Table 2). These values are believed to be conservative, based on Dunrud's annual observations over the last seven years in the Apache Rocks mining area. • Panels E1 to E8: For these eight panels, projected horizontal tensile strain ranges from 0.004 to 0.022 (0.4 to 2.2 percent) where the planned coal extraction thickness is 8 feet; from 0.007 to 0.027 (0.7 to 2.7 percent) where the extraction thickness equals 12 feet; and from 0.007 to 0.039 (0.7 to 3.9 percent) where the extraction thickness equals 14 feet. Horizontal compressive strain ranges from -0.004 to -0.024 (-0.4 to -2.4 percent) where the extraction thickness equals 8 feet; -0.007 to -0.029 (-0.7 to -2.9 percent) where the thickness equals 12 feet; and -0.007 to -0.042 (-0.7 to -4.2 percent) where it equals 14 feet (Table 2). • Panel E9: Predicted horizontal tensile strain in this single panel ranges from 0.018 to 0.027 (1.8 to 2.7 percent) where the coal extraction thickness equals 12 feet and 0.021 to 0.031 (2.1 to 3.1 percent) where the extraction thickness equals 14 feet. Compressive strain this panel is predicted to range from -0.018 to -0.029 (-1.8 to -2.9 percent) where the extraction thickness equals 12 feet and -0.021 to-0.034 (-2.1 to -3.4 percent) where it equals 14 feet (Table 2). Tetra Tech - 090717/P 10