PERMFILE123352 - Laserfiche WebLink

Home Browse Search

Subsidence Evaluation For Exhibit 60 The Apache Rocks And The Box Canyon Mining Areas Page 16 • 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 compaze favorably. Baseline subsidence measurements in the current West Elk mining area were selected such that subsidence parameters from longwall mining in the B-Seam were obtained with as little influence from prior room-and-pillar mining as possible. In this way the longwall mining subsidence parameters from the current West Elk mining azea could be used to most accurately project longwall mining subsidence parameters into the Apache Rocks and the Box Canyon mining areas. The baseline subsidence measurement selected for both conceptual modeling and computer modeling was October 1991, which was before B-Seam longwall mining began and aRer 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 the Apache Rocks and the Box Canyon mining areas for the various overburden depths in order to obtain an independent check on the subsidence projections based on the conceptual model (Tableland Figure 6). Comparison of the author's conceptual model and the influence function computer model of Peng and Luo show the following: 1. Subsidence above the chain pillars and panel centers of the computer model for the Apache • Rocks mining area is approximately at the median point of the conceptual model data presented for the eastern and western panels (Table 2 and Figures 7a and 7b). 2. Subsidence above the chain pillars and panel centers for the Box Canyon mining area also is at about the median point of the conceptual model data for the first four panels (Table 3 and Figure 7c). 3. Subsidence above chain pillars and panel centers of the computer model for the Box Canyon mining area is less than the values predicted by the conceptual model data for panels 4 through 6 (numbered from north to south). This difference is because the computer program calculates that this thick overburden (as much as 2,300 feet beneath West Flatiron) will subside into individual panels and that the chain pillars will support or partially support the overburden. However, based on longwall mine subsidence experience in other coalfields in the Western United States, it is estimated that panels 4 through 6 may, at least locally, behave as a super panel of supercritical width. The chain pillars (assuming dimensions similar to the current West Elk Mine longwall mining area) will yield and crush out afrer mining to approximately 0.6 times the coal extraction thickness (the model actually shows this to some extent). 4. The conceptual model subsidence prediction results are presented in ranges that make them more conservative than the computer model results. The computer model results are close to • the median values of the conceptual model. 831-032.181 Wright Water Engineers, Inc.