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+. mining methods on the subsidence network. The grid has also verified MCC's predicted <br />subsidence and established when subsidence occurs, where it occurs, and when it is complete. <br />The grid demonstrated, in regazd to longwall mining, that the majority of the subsidence was <br />seen within the first year after mining, and in most cases subsidence was completed within one <br />year to a yeaz and-a-half. This information and its usefulness in predicting subsidence <br />parameters in the adjacent Apache Rocks and Box Canyon mining azea is detailed in the <br />following section. In addition, some general observations obtained from the West Elk Mine and <br />neighboring mining operations are described below. <br />Detailed Description of Predicted Subsidence Phenomena - 2.05.6 (6)(e)(i)(D) <br />Subsidence, as it relates to mining, is defined as the local downwazd displacement of the surface and <br />the overburden rock in response to mining under the influence of gravity. The following text <br />includes a general discussion of the various zones defined within the subsidence azea; predicted <br />maximum vertical and horizontal displacements, tilt, curvature and horizontal strain; predicted <br />zones of tensile strain related to mine geometry; predicted rates and duration of subsidence; the <br />effects of topography on subsidence; and the predicted angle of draw. A summary of these values <br />as determined from the present mining area subsidence monitoring data is presented in Table 1, <br />Exhibit 60. Table 2 and Table 3 in Exhibit 60 summarizes the projected values of these parameters <br />for the Apache Rocks and Box Canyon mining areas in the following subsidence discussion. <br />Subsidence Zone Description <br />• For purposes of describing subsidence effects on overburden material and the ground surface, <br />subsidence can be divided into four zones (see Figure 1 in Exhibit 60 for details): (1) Caved zone, <br />(2) Fractured zone, (3) Continuous deformation zone, and (4)Near-'surface zone. <br />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. Rotation of the caved debris occurs during the fall so that the <br />caved fragments tend to pile up in a random fashion. This caved izone, according to Peng (1992), <br />occurs for the first 2 to 8 mining thicknesses (2 to 8t) in the roof rocks. In the current West Elk <br />Mine longwall panels, the caved zone is estimated to be 2.5 mining thicknesses (2.St) based on roof <br />rock observations from directly behind the current longwall equipinent. Any water present in this <br />zone will drain into the mine almost immediately after caving occurs. <br />The B and E-Seam roof rocks commonly consist of thinly bedded cazbonaceous shales, sandy <br />shales, claystones, and sandstones. A soft shale that is susceptible to air slaking forms the <br />immediate roof of the B-Seam in most areas. Thick sandstones locally form the immediate roof of <br />the E-Seam, in addition to the shales and sandstones. <br />The ratios of shale to sandstone aze quite similaz in the first 20 feet of roof in the B and E-Seams. <br />The shale to sandstone ratio of the first 20 feet of B-Seam roof averages about 2:3, the shale to <br />sandstone ratio of the fast 5 feet averages 3:2. The shale to sandstone ratio of the first 20 feet of the <br />• E-Seam roof is 3:2; the shale to sandstone ratio of the first S feet is also 3:2. Although the <br />2.05-I ]2 March 2005PR11 <br />~ 1.05 <br />