PERMFILE103730 - Laserfiche WebLink

Home Browse Search

West Elk Mine • data, the actual subsidence measurements and subsidence profiles predicted by the influence function model compaze 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-pillar 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 SOD 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-pillar mining was completed in the subsidence monitoring network area. Once the computer program was calibrated to the West Elk Mine subsidence data, subsidence was projected into the SOD mining azeas 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 and Figure 7, Exhibit 60B). Apache Rocky and Box Canvon Minin Areas -Comparison of the two models shows that subsidence values above the chain pillars and panel centers of the computer model for the Apache Rocks mining area aze approximately at the median point of the conceptual model data presented for the eastern and western panels (Table 2 and Figures 7a and 76, Exhibit 60). Subsidence above the chain pillars and panel centers for the Box Canyon mining area is also at about the median point • of the conceptual model for the first four panels (Table 3 and Figure 7C, F_xhibit 60). South of Divide Mining Area -Comparison of Mr. Dunrud's conceptual model calculations and the influence function computer model of Peng and Luo (which were done by the WWEs staff in Figures 7 and 8, Exhibit 60B) show the following: 1. Maximum vertical displacement (subsidence) above the chain pillars in the transverse profile (Figure 7, Exhibit 60B) is close to the maximum values predicted in the conceptual model calculations (0.8 to 4.2 feet). Maximum vertical displacement above the longwall panel centers, however, is about equal to the median values projected in the conceptual model calculations (4.8 to 11.2 feet). 2. The ranges calculated for vertical displacement in the conceptual model are conservative. The ranges account for changing rapidly changing overburden thickness in the local rugged terrain of the South of Divide mining area and for changing lithology such as lenticular sandstones, coal seams, and shales in the overburden rocks. Effects of Topography and Structure on Subsidence Processes In contrast to subsidence of rock units behaving asfixed-end, laterally constrained, multiple plates, subsidence in steep topography will typically occur as non-fixed end, laterally unconstrained multiple plates (rock units). This lack of lateral confinement may locally cause • reversals of horizontal displacement and excessive tensile strain on steep slopes. Peng and Hsuing (1986) found that horizontal displacement is affected by slopes greater than 20 percent. 1.05-123 RevrsedNwember 2004 PRIO