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2004 Geologic Hazard Field Observations <br />South of Divide Mining Area <br />CJ <br />7.0 SUBSIDENCE PREDICTION BASED ON PAST LONGWALL MINING <br />Coalmine subsidence, as defined in this report, is the local downwazd displacement <br />(downwarping) of the ground surface and underlying rocks above the mined coal under the <br />influence of gravity. This report includes only a brief summary, see Exhibits 60 and 60B, dated <br />November 2004 for greater detail. Subsidence above longwall mining panels can be divided into <br />four zones, which conceptually chazacterize the subsidence processes occurring from the mine <br />workings to the surface: 1) caved zone, 2) fractured zone, 3) continuous deformation zone, and 4) <br />neaz-surface zone. The continuous deformation and near-surface zones are usually combined, so <br />that the zones aze reduced to three (the continuous deformation and near-surface zones will also <br />be evaluated together in this report). <br />Subsidence causes the overburden material above longwall mining panels to: 1) cave into rubble <br />for the first 2 to 5 coal extraction thicknesses (2 to St) above the mine floor (caved zone); 2) <br />fracture for the next 10 to 20t (fracture zone); and 3) deform downwazd (down warp) as <br />• continuous, multiple layers (or plates) from the limit of the fracture zone to the ground surface <br />(continuous deformation and neaz-surface zone). <br />• <br />7.1 Vertical and Horizontal Displacement, Tilt, Curvature, and Horizontal Strain. <br />Differential vertical lowering of the ground surface causes vertical displacement (S), horizontal <br />displacement (S b), tilt (NI), curvature (C), and horizontal strain (E). Vertical displacement (also <br />called subsidence), tilt, and strain aze the main subsidence pazameters used in most subsidence <br />studies, and therefore, these will be the ones discussed in this report. <br />Vertical displacement, tilt, and horizontal strain predictions for the South of Divide mining area <br />are determined from the baseline data obtained from subsidence measurements above the 1NW, <br />2NW, and 3NW mining panels at West Elk Mine (Table 1). The basic subsidence parameters aze <br />then adjusted to geologic and topographic conditions in the areas where mining is planned. The <br />subsidence pazameters, projected for the South of Divide mining azea, are listed below. <br />831-032.621 Wright Water Engineers, Inc. Page 12 <br />November 2004 <br />