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Subsidence Evaluation For Exhibit 606 South of Divide Mining Area Page 14 • 5.8 Critical Extraction Width of Mining Panels Critical extraction width (We) is the width of mining panels necessary for maximum subsidence to occur at a given overburden depth (d). Values for W„/d typically range from about I.0 to 1.4, with an average of about 1.2. Based on the subsidence development data for the 5th IVyV longwall panel, the critical extraction width may be closer to the average value of 1.2 than 1.4 in the South of Divide mining area (Figure 4). 5.9 Results of Computer Modeling A computer software package was used to model the results of subsidence measurements at West Elk Mine and to project subsidence in the South of Divide mining area_ The package used is entitled: "Comprehensive and Integrated Subsidence Prediction Model (CISPM)," Version 2.0, by Syd S. Peng and Yi Luo, Department of Mining Engineering, College of Mineral and Energy Renounces, West Virginia University, Morgantown, West Virginia. This program performed an influence function analysis and best fit of West Elk Mine subsidence data. The fit between the data points and the influence function output from dte model is shown in Figure 6. Considering that there was some F Seam influence on the B Seam subsidence data, the actual subsidence measurements and subsidence profiles predicted by the influence function model compare favorably. Baseline subsidence measurements in the current West Elk Mine subsidence monitoring area • were selected such that subsidence parameters from longwall mining in the B Seam were obtained with as little influence from prior room-and-pillaz mining as possible. in this way, the longwall mining subsidence parameters from the monitoring area could be used to most accurately project longwall mining subsidence parameters into the South of Divide mining area. The baseline subsidence measurements selected for both conceptual modeling and computer modeling were October 1991, which was before B Seam longwall mining began and after F Seam room-and-pillaz mining was completed in the subsidence monitoring network area. Once the computer program was calibrated to the West Elk Mine subsidence data, subsidence was then projected into South of Divide mining area using representative coal extraction thicknesses and overburden depths for the respective panels in order to obtain an independent check on the subsidence projections based on the conceptual model (Table 1). Comparison of the author's conceptual model and the influence function computer model of Peng and Luo show the following: Comparison of the author's conceptual model calculations and the influence function computer model of Peng and Luo {which were done by the Wright Water Engineers, Inc. in Figures 7 and 8) show dre following: 1. Maximum vertical displacement (subsidence) above the chain pillars in the transverse profile (Figure T) is close to the maximum values predicted in the conceptual model calculations. Maximum vertical displacement above the longwall panel centers, however, is about equal to the median values projected in the conceptual model calculations. 831-032690 WiigMWaterF~gineers, tnc.