Laserfiche WebLink
February 1, 2010 Page 3 <br />2.1 Model Geometry <br />There have been multiple slope stability analyses performed (Agapito 2008b, 2009a, and <br />2009b) for the K -Pit mining plan; as new information becomes available, geometry and material <br />properties are updated to give the most accurate estimate of the global stability of the pit and <br />spoil areas. The locations for the previous analysis were picked based on the steepest slope of <br />the most likely failure surface (see Figure l). For the initial K -Pit buttress analysis, the sections <br />were aligned with the maximum slope of the fill. For the K -Pit mining analysis, the sections <br />were aligned with the maximum slope of the Q -Seam coal. For this round of modeling, the <br />middle section from the K -Pit mining models (Section -4) was used, as there was little difference <br />in the results of the other sections and K..l -Block is the first area to be mined. <br />The reason for performing a two- dimensional (21)) analysis, as opposed to a three - <br />dimensional (31)) analysis was because of the lack of variability of the K -Pit geometry and spoil <br />thickness in the lateral direction of the dip, both within the K -Pit and most importantly within the <br />toe- buttress structure. The lithology for the section was obtained from a cross - section provided <br />by TMI. The section was labeled "Section -4." The dip of the R -Seam floor varied from 9 -13 <br />in the model. The highwall on the north end of the pit was modeled with a slope of 1 H:2V up to <br />the L -Seam floor, and with a slope of 1 H:1 V from there above, based on the mine plan <br />information provided by TMI. Figure 2 shows the pit configuration at various points in time, <br />based on the cut sequence provided by TMI. <br />The phreatic surfaces assigned to the model were initially generated with the aid of data <br />obtained from two piezometers installed within the K -Pit. Preliminary phreatic surfaces assigned <br />to the models were projections of the most recent recorded piezometric levels at these two <br />piezometers within the K -Pit and their horizontal extrapolations beyond the K -Pit. After further <br />consideration, AAI believes that although the field piezometrrc data may represent in -pit <br />subsurface- seepage conditions accurately, they may not be appropriate to predict hydrologic <br />conditions underneath the toe buttress. AAI believes that long -term seepage under the buttress <br />will be controlled by the interface such as the one between the strata I1 -I2 interburden sandstone <br />and Q -Floor mudstone, which have high differential permeability. In addition, short-term <br />infiltration due to rainfall or snowmelt could cause saturated zones within the overburden layer. <br />Being consistent with the original modeling of the K -Pit buttress area, the phreatic <br />surface was assumed to be at the base of the buttress, which is the worst probable scenario. <br />2.2 Methodology <br />SLOPUW was used for this phase of the analysis using the Morgenstern-Price slide <br />function along with the grid and radius slip - surface generating feature of the software. This <br />modeling technique allows the program to calculate the FOS for every possible slip plain that <br />can be drawn with a center at each point on the grid and each specified radius. <br />2.3 Material Properties <br />Properties of all. the geologic layers, except for the spoil, simulated in the models were <br />the same as material properties calibrated during the G -Pit landslide analysis. The material <br />Agapito Associates, Inc. <br />