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West Elk Mine <br />again under lateral vertical compression associated with static conditions, and become <br />impermeable again. <br />Within the permit area, fracturing will likely become discontinuous with increasing height because <br />of the alternating sequence of harder and brittle and softer and yielding rocks. Steeply dipping <br />fractures near the top of the caved zone, therefore, will likely become less continuous with <br />increasing height in the zone of fracturing. Also, with increasing height in this zone, and as <br />lateral and vertical constraints increase, fracturing that could impact water bearing zones will tend <br />to occur more in zones of convex upward curvature, along sepazated bedding planes toward the <br />center of the panel, and along local cracks in zones of convex downward curvature (Figure 1, <br />Exhibit 60. Fracturing within the expected zone of fracture may cease completely where soft <br />shales and claystones occur as alternating sequences with sandstone. <br />Mr. Dunrud has concluded that the maximum height of fracturing above longwall panels in the B- <br />Seam in the Apache Rocks mining area is estimated to range fmm about 15 to 20 times the <br />extraction thickness (t) (for example, if t = 12 feet, the maximum fracture height would be 240 <br />feet at 20t) neaz the mid-range of 9 to 30 times coal extraction thickness. This estimate is viewed <br />as conservative by Mr. Dunrud because rocks above the B-Seam and below the Marine <br />Sandstone, that underlies the D-Seam, consist of about 150 to 200 feet of laminated sandstone and <br />shale and sandy shale and sandstone. Most fractures will likely become discontinuous at the base <br />of the marine sandstone and may be located only in the following areas: (1) azeas of tension near <br />areas of convex upward curvature above chain pillars; (2) along local bedding planes; and (3) <br />areas of convex downward curvature above the longwall panels. <br />Continuous Deformation Zone and Near-Surface Zone <br />These two zones are discussed together because the ground surface is where nearly all <br />measurements are made that monitor subsidence processes active in the zone of continuous <br />deformation. The near-surface zone, which typically consists of weathered bedrock, colluvium, <br />and soil ranging in depth from a few feet to a few tens of feet, may deform differently than the <br />underlying bedrock, especially on steep slopes. The zone of continuous deformation, which is <br />transitional to the underlying zone of fracturing, consists of differential vertical lowering and <br />flexure of the overburden rocks above the zone of caving and fracturing. <br />Maximum Verdical and Horizontal Displacement. Curvature. Tilt. Horizontal <br />Strain. and Depth of Surface (Tensile) Cracks <br />Differential vertical lowering causes vertical displacement (S), horizontal displacement (S,J, tilt <br />(M), curvature (C), and horizontal strain (E). Each of these parameters are graphically illustrated <br />in Figure 2, Exhibit 60. In flat or gently sloping terrain (slopes less than about 20 percent), <br />surface profiles of subsidence depressions are similar to flexure of fixed-end, laterally constrained <br />beams. Tensile stresses aze present in areas of positive curvature decreasing to zero at the neutral <br />surface before which they reverse to become compressive stresses (see Figure 1, Exhibit 60). <br />• <br />2.05-114 Jar,aary 1998 PR08 <br />