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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 9 <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />5.0 SUBSIDENCE PREDICTION BASED ON LONGWALL MINING AT <br />WEST ELK MINE <br />Subsidence, as it relates to longwall mining, is defined herein as the local downward displacement <br />of the surface and overburden rock in response to mining under the influence of gravity. For <br />purposes of describing subsidence effects on overburden material and the ground surface, <br />subsidence can be divided into four zones (Figure 2): 1) caved zone, 2) fractured zone, 3) <br />continuous deformation zone, and 4) near surface zone. <br />5.1 Caved Zone <br />As coal is extracted and a void is produced, the roof rocks break along bedding planes, joints, and <br />fractures and fall to the mine floor (Figure 2). Rotation of the caved debris occurs during the fall <br />so that the caved fragments tend to pile up in a random fashion. This caved zone, according to <br />Peng (1992, p. 1-2) occurs for the first 2 to 8 mining (or coal extraction) thicknesses (2t to 8t) in <br />the roof rocks (for example, if t=12 feet, the caved zone would range from 24 to 96 feet [2t to 8t]). <br />According to Wendell Koontz, former senior geologist at West Elk Mine, this caved zone averages <br />about 2.5t for longwall mining of the B-seam in the West Elk Mine. This includes the Apache <br />Rocks and Box Canyon mining areas (Koontz, oral communication March 2004). <br />Based on the stratigraphic and lithologic information obtained from drill holes in the Southern <br />Panels and Sunset Trail mining areas, the rocks consist of a greater proportion of shales, siltstones, <br />and claystones than are present in the Apache Rocks and Box Canyon mining areas. The height <br />of the caved zone is therefore projected to range from 2t to 5t, depending on water conditions <br />encountered and on specific roof lithology. In a dry environment, where lenticular sandstones <br />comprise the E-seam roof, the caved zone will be closer to 2t. In a wet environment where soft <br />shales and claystones occur in the roof, however, the caved zone will likely be closer to 5t. The <br />average height of the caved zone is projected to average 3t in the Southern Panels and Sunset Trail <br />mining areas. <br />5.2 Fractured Zone <br />A zone of fracturing and local separation along rock bedding planes and joints occurs above the <br />zone of caving (Figure 2, Enlargement 1). In this zone, which is transitional to the underlying <br />caved zone, lateral and vertical constraints in the adjacent overburden strata and the caved rocks <br />below prevent further large displacement or rotation of the fractured rock. Displacements in the <br />fracture zone and severity of fracturing tend to decrease upward as lateral and vertical confining <br />stresses increase. <br />Based on width and conductivity of fractures Peng (1992, p. 143) states that the upper one-third <br />of the fractured zone (in terms of height) has only minor fractures with little potential for water <br />conductivity. In the lower two-thirds of the fractured zone, water conductivity commonly <br />increases progressively downward. <br />Compression arches (arcuate zones of compressive stress) commonly develop, or partially <br />develop, above the mining panels. These arches temporarily transfer overburden stresses to the <br />panel barrier or chain pillars and to the caved gob and the mining face (Dunrud 1976). Stresses