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Subsidence Evaluation For <br />Exhibit 60 The Apache Rocks And The Box Canyon Mining Areas Page 11 <br />• curvature projected in the westem panels for E- and B-Seam mining ranges from approximately <br />-0.00026 to -0.00132 rad/ft. <br />Box Canvon Minine Area. Maximum positive curvature for the two northem panels, Panels 1 <br />and 2, is projected to be 0.000030 to 0.000410 rad/ft; for Panel 3, 0.000024 to 0.000202 rad/ft; <br />for Panels 4 through 6, 0.000016 to 0.000239 rad/ft. Similarly, maximum negative curvature is <br />projected at -0.000022 to -0.000410 rad/ft for Panels 1 and 2; -0.000024 to -0.000202 rad/ft for <br />Panel 3; -0.000016 to -0.000239 rad/ft for Panels 4 through 6. <br />4.3.1.5 Maximum Horizontal Strain <br />Maximum horizontal tensile strain (Em) measured in the West Elk Mine monitoring network <br />ranges from 1.12 to 1.4~(Sm /d) (0.0058 to 0.0102) (Table l). The range of horizontal tensile <br />strain in four different mine areas of the Westem United States studied by the author is 0.45 to <br />3~(Sm/d). Using an average value of 1.3•(Sm/dj for maximum predicted horizontal tensile strain <br />above the chain pillazs, the gate road entries, and bamers behveen panels and an average of <br />2•(Sm/d) for maximum predicted horizontal compressive strain, the following strain values are <br />projected for the Apache Rocks and the Box Canyon mining areas (Tables 1, 2 and 3): <br />Apache Rocks Mining Area. The horizontal tensile strain in the eastern panels after B-Seam <br />• mining is projected to range from 0.003 on the south flank of West Flatiron (overburden depth is <br />about 2,250 feet) to 0.013 (units are dimensionless [L/L]) near the head of Sylvester Gulch <br />(Table 2). <br />Projected horizontal tensile strain for the western panels for E-Seam mining are 0.008 above the <br />thickest overburden on the ridges to 0.023 above the thinnest overburden in Horse Gulch. <br />Tensile strain after both E- and B-Seam mining is completed may range from about 0.016 to <br />0.041 above thickest and thinnest overburden, respectively. <br />Projected horizontal compressive strain will be in the panel centers. [n the eastem panel azea, <br />using an average value of 2.0~(Sm/d) from the West Elk Mine subsidence network, compressive <br />strain is projected to range from -0.004 near the south flank of West Flatiron to -0.020 near the <br />head of Sylvester Gulch. Compressive strain above the westem panels after E-Seam mining is <br />estimated to range from -0.013 in areas of thickest overburden to -0.035 in areas of thinnest <br />overburden. After mining both the E- and B-Seams, compressive strain is estimated to range <br />from -0.02 to -0.062 in thickness for thickest and thinnest overburden, respectively. <br />Box Canvon lvtining Area. Maximum projected horizontal tensile strain in the Box Canyon <br />mining area is expected to range fiom 0.002 at West Flatiron (overburden depth about 2,300 feet) <br />to about O.Ol7 above the northern panel center beneath Box Canyon and the unnamed canyon to <br />• the west, where the minimum overburden depth above the centerline of the northem panel is <br />831-032.181 Wright Water Engineers, Inc. <br />