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To: Chris Nyikos, Project Manager - Mountain Coal Company <br />Subject: Geotechnical Review of Updated PR-2 Conveyor Alignment <br />Date: July 17, 2009 <br />Project: 06/26-1004 <br />Slope stability was initially analyzed using geometry based on the existing ground surface. For each of <br />the two modeled cross-sections, a colored "safety map" was plotted beneath the ground surface <br />representing various factors of safety and illustrating respective potential circular failure surfaces. With <br />this information, the factor of safety versus horizontal distance from a common point could be estimated <br />along the ground surface. <br />The factor of safety increases as the point of interest on the ground surface moves away from the edge of <br />the slope crest. Using these results, a graph was produced showing factor of safety versus distance for the <br />conveyor alignment. In this manner, a factor of safety for each cross-section station could be estimated <br />based on the slope stability analysis performed at the representative cross-section. Table 1 shows the <br />results of this exercise. <br />Based on the qualifying criteria listed below the table, the analysis shows factors of safety for Stations <br />1+00 through 12+00 to be less than 1.20, indicating that stabilization is required. Stations 13+00 through <br />16+00 are considered as locations potentially requiring stabilization, with factors of safety between 1.2 and <br />1.5. <br />A second analysis looked for improved safety factors associated with excavating a hillside bench along the <br />alignment and supporting a majority of the conveyor on concrete blocks placed upon the bench. Block <br />support reduces the risk associated with constructing bents on the existing ground surface, as bents can <br />rotate with continued landslide displacements and cause significant problems for conveyor alignment. <br />Additional benefits of this approach include: the concrete block supports are easily adjusted back into <br />alignment to counter continued movement of the overall landslide; construction of stabilization measures is <br />less problematic with bench access; and factors of safety for each support generally increases as the crest of <br />the slope is unloaded through the excavation of material above the bench. The factors of safety, as shown <br />in Table 1, increase in nearly all cases. Although the computed factors of safety for Stations 13+00 and <br />14+00 decreased due to a change in criteria, the need for stabilization remained unchanged. <br />Conveyor Support Blocks and Bents <br />As proposed in the original review for conceptual design purposes, the concrete conveyor support blocks <br />are combined with two drilled shafts, approximately 40 feet deep, located on the downslope edge of a <br />concrete slab. Each drilled shaft would comprise a W or HP steel pile in an auger drill hole, backfilled <br />-4-