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Subsidence Evaluation for the <br /> Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 10 <br /> temporarily increase in the zones of these compression arches. However, the arches in a given <br /> area commonly move upward and dissipate as longwall mining is completed in that area. Arches <br /> may not dissipate where the room-and-pillar mining method is used, because pillars and stumps <br /> left after mining can prevent dissipation of the compression arches. The overburden rocks affected <br /> by the arches are temporarily subjected to increased stress and strain as the arches move upward. <br /> In longwall mining areas, this increased stress and strain commonly are less than in room-and- <br /> pillar mining areas because stresses are relieved as the arches move upward and dissipate. <br /> Peng(1992,p.4)reports that the combined height of the zone of caving and fracturing ranges from <br /> 20t to 30t, and that the height of the fractured zone is greater for hard, strong rocks than for soft, <br /> weak rocks. <br /> The height of the zone of fracturing is a function of lithology and layer thickness, according to <br /> Peng (1992, p. 6-8). For example, the zone of fracturing commonly is higher for strong, thickly- <br /> bedded, brittle sandstones than it is for thinly layered, soft, shales and claystones. Liu (1981) <br /> reports ranges of heights of the zone of fracturing for various rock types as follows: <br /> 1. Heights of 20t to 30t are reported in strong brittle rocks, such as siliceous sandstones and <br /> limestones; a value of 28t was reported for overburden containing 70 percent sandstone. <br /> Also, because of hardness, fractures do not close as readily in brittle rocks as they do in <br /> soft rocks during recompression. <br /> 2. Heights of 9t to 1 It are reported where all the rocks consist of soft shales and claystones. <br /> The fractures also commonly close again under stresses associated with static conditions, <br /> and become impermeable again. <br /> Considering the lithology of the areas, Mr. Koontz estimated that 10t to 20t was a good projection <br /> for the height of fracturing in the Apache Rocks and Box Canyon mining areas. However, a <br /> projected fracture height of 30 times the coal extraction thickness(30t)may locally occur(Koontz, <br /> oral communication March 2004). <br /> Within the Southern Panels and Sunset Trail mining areas, the fracture zone may become less <br /> continuous in the caved zone with increasing height because of the alternating sequence of harder <br /> and brittle rocks and softer and yielding rocks. The height of the fracture zone, therefore, will <br /> likely be lessby possibly 10 to 20 percent—than the height predicted for the Apache Rocks and <br /> Box Canyon mining areas because of the presence of more shale above the E-seam mining in the <br /> Southern Panels and Sunset Trail mining areas. Fractures near the top of the caved zone,therefore, <br /> will likely become less continuous with increasing height in the zone of fracturing. <br /> The maximum height of fracturing above longwall panels in the Southern Panels and Sunset Trail <br /> mining area is estimated to range from about 10t to 20t. This is near the mid-range of 9t to 30t as <br /> reported by Peng (1992, p. 7). This estimate may be conservative for the particular rock strata or <br /> lithology above the E-seam. When considering a conservative 10 percent reduction for the softer <br /> rocks overlying the E-seam, the effective height of fracturing in the Southern Panels and Sunset <br /> Trail mining areas is estimated to range from 9t to 18t. <br /> 831-032.912 Wright Water Engineers, Inc. <br /> December 2020 <br />