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May 28, 2009 Page 2 <br />¦ The stability analysis was performed using the two-dimensional (21)) numerical modeling <br />program, FLAC/Slope.3 This analysis used calibrated rock mass properties obtained from the <br />1 G-Pit landslide FLAOD stability analysis and spoil properties obtained during field <br />investigations and literature review.""" The stability of the toe buttress along three different <br />cross sections was investigated. <br />2.1 Model Geometry <br />In total, three different 2D numerical models were developed, each representing a <br />different cross section taken through the K-Pit and the proposed toe buttress. Due to differences <br />in original topography, both the K-Pit and toe-buttress configuration varied for the three sections. <br />' These sections were called the East, Mid and West sections, based on their relative location. <br />Model boundaries were developed based on the stratigraphic cross sections provided by TMI. <br />The East section ran through point 1,436,922E, 401,890N, at elevation 7,538.5 feet, along a <br />N73°E direction; the Mid section ran through point 1,436,001E, 402,494N, at elevation <br />7,530 feet, along a N78°E direction; the West section ran through point 1,436,329E, 401,932N, <br />at elevation 7,587 feet, along a N71°E direction. The plan view of the chosen sections relative to <br />the K-Pit and toe buttress is presented in Figure 1. The sections were chosen in such a manner so <br />as to represent the steepest gradient of the toe buttress foundation and thickest cross section of <br />the structure itself. The vertical boundaries of the preliminary numerical models extended from <br />the southern end of K-Pit to the northern end of the toe buttress. However, the southern ends of <br />the model boundaries were later truncated at the K-Pit highwall in order to optimize the <br />computing effort. <br />¦ The reason for performing a 2D analysis, as opposed to a three-dimensional (31)) <br />analysis, was the lack of variability of the K-Pit geometry and spoil thickness in the lateral <br />direction of the dip, both within the K-Pit and most importantly within the toe-buttress structure. <br />The geometries of the geologic layers along the three selected sections were provided by TMI. <br />The dip of the R Seam floor varied from 9 to 13 degrees in all the models. The highwall on the <br />' north end of the pit was modeled with a slope of 1H:2V up to the L Seam floor and with a slope <br />of 1H:1V from there above, based on the mine plan information provided by TMI. <br />Representative model geometries for all three sections are presented in Figures 2a-c. <br />In all the models developed, the pre-slide topography was used as the foundation surface <br />of the toe buttress. A 25-ft-thick overburden layer was assumed to be underlying the spoil <br />' buttress in all the models. To simplify the geometry of the models developed, the underlying <br />geologic layers as diverse as coal, sandstone, mudstone, etc., were bundled into larger and more <br />representative layers. Thus, a 29.5-ft-thick layer of the 11 Seam followed the overburden layer, <br />' which in turn was underlain by a 37-ft-thick sandstone layer (representing I1-I2 interburden). <br />I <br />3 FLAC/Slope (2005), "Fast Lagrangian Analysis of Continua-User's Guide," Itasca Consulting Group, <br />Inc., Minneapolis, MN, Version 5.0. <br />a Douglass, P., and M. Bailey (1983), "Evaluation of Surface Coal Mine Spoil Pile Failures," Third <br />International Conference on Stability in Surface Mining, Vol. 3, pp. 815-836. <br />5 Capstone Enterprises West, LLC. (2008), "Geologic Review and Soils Engineering Report," prepared <br />for Trapper Mining, Inc., June 4. <br />Agapito Associates, Inc.