Laserfiche WebLink
West Elk Mine <br />Rate and Duration of Subsidence <br />A point on the surface begins to be affected when the longwall mining face is within O.ld to O.bd <br />(d =mining depth). This goint attains maximum downwazd velocity when the face is 0.2 to O.Sd <br />beyond the point. This corresponds with a time when subsidence is approximately 50 percent <br />complete. Subsidence is more than 90 percent complete when the longwall mining face is 1.0 to <br />1.4d (average about 1.2d) beyond the point Figure 8, Exhibit 60). <br />Rate and duration of subsidence above longwall mining panels, therefore, aze a function of mining <br />rate. The faster and more uniformly the longwall mining occurs, the less time any surface cracks <br />present will be open to potentially impact surface or ground water. <br />The duration of subsidence above room-and-pillar mines; however, is less predictable because not <br />all pillars are removed. For example, in Figure 8 of Exhibit 60, subsidence at a given point (p) <br />was only about 60 percent complete after mining was completed within the area of influence of <br />the point. <br />Results of Computer Modeling <br />A computer software package was used to model the results of subsidence measurements at the <br />West Elk Mine and to project subsidence amounts in the Apache Rocks and Box Canyon mining <br />• areas. The package used is entitled "Comprehensive and Integrated Subsidence Prediction Model <br />(CISPM)," Version 2.0, by Syd S. Peng and Yi Luo, Department of Mining Engineering, <br />College of Mineral and Energy Resources, West Virginia University, Morgantown, WV. This <br />program performed an influence function analysis and best fit of the West Elk Mine subsidence <br />data. The fit between the data points and the influence function output from the model aze shown <br />in Figure 6, Exhibit 60. Considering that there was some F-Seam influence on the B-Seam <br />subsidence data, the actual subsidence measurements and subsidence profiles predicted by the <br />influence function model compare favorably. <br />Once the computer program was calibrated to the West Elk Mine subsidence data, subsidence was <br />projected into the Apache Rocks and the Box Canyon mining areas for the various overburden <br />depths and mining sequences in order to obtain an independent check on the subsidence <br />projections based on the conceptual model (Table 1 and Figure 6, Exhibit 60). Compazison of the <br />two models shows that subsidence values above the chain pillars and panel centers of the <br />computer model for the Apache Rocks ntinntg area are approximately at the median point of the <br />conceptual model data presented for the eastern and western panels (Table 2 and Figures 7a and <br />7b, Exhibit 60). Subsidence above the chain pillazs and panel centers for the Box Canyon mining <br />area is also at about the median point of the conceptual model for the first four panels ('T'able 3 <br />and Figure 7C, Exhibit 60). The concepmal model subsidence prediction results are presented in <br />ranges that make it more conservative than the computer model results. <br />Ia <br />2.05-123 RevisedJun. 1995 PR06; !!96 RN03; RevisedJmi. 1998 PROS <br />