2022-09-29_PERMIT FILE - C1980007 (5)

Home Browse Search

Subsidence Evaluation for the Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 17 831-032.923 Wright Water Engineers, Inc. December 2021 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 Southern Panels mining area, based on the West Elk Mine 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 above barrier pillars or the interface of mined and unmined coal at the limits of mining (e.g., mineable coal or lease boundary) than chain pillars because of their greater 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 Southern Panels mining area. Maximum horizontal tensile strains, measured Dunrud in bedrock during annual observations in the Apache Rocks West 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 West mining 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 West mining area. Southern Panels Mining Area: Maximum tensile and compressive horizontal strains are calculated, using the values obtained from the area of the West Elk Mine, and as projected in Figure 5 (Table 2). These values are believed to be conservative, based on Dunrud’s annual observations in the Apache Rocks West mining area. • Panels E1 to E8 and E14 to E17: For these panels, projected horizontal tensile strain ranges from 0.005 to 0.028 (0.5 to 2.8 percent) where the planned coal extraction thickness is 9 feet, and from 0.007 to 0.044 (0.7 to 4.4 percent) where the extraction thickness equals 14 feet. Horizontal compressive strain ranges from -0.005 to -0.030 (-0.5 to -3.0 percent) where the extraction thickness equals 9 feet, and -0.007 to -0.047 (-0.7 to -4.7 percent) where it equals 14 feet (Table 2). • Panels B26 to B29: For these panels, projected horizontal tensile strain ranges from 0.004 to 0.017 (0.4 to 1.7 percent) where the planned coal extraction thickness is 9 feet, and from 0.007 to 0.026 (0.7 to 2.6 percent) where the extraction thickness equals 14 feet.