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To: Chris Nyikos, Project Manager - Mountain Coal Company <br />Subject: Stability Analysis of LRP With Preparation Plant <br />Date: 8 September, 2009 <br />Project: 06/26-1004 <br />factor of safety was greater than 1.50, indicating the LRP is stable under the proposed slope geometry and <br />assumed building loads. <br />The results of the pseudo-static analysis using the 475 year return period (PGA=0.0698g) indicate factors <br />of safety of 1.56 and 1.68 for cross sections A and B, respectively. The model outputs are shown in Figures <br />3 and 4, respectively. For the pseudo-static analysis using the PGA of 0.166g, the resulting factors of safety <br />are 1.26 and 1.37 for cross sections A and B, respectively. The model outputs are shown in Figures 5 and <br />6, respectively. In both cases, the resultant factor of safety was greater than 1.20, indicating the LRP is <br />stable under the proposed slope geometry and assumed building loads. <br />Output reports indicating all model inputs and results for the runs shown in Figures 1-6 are attached in the <br />Appendix. <br />The results of the analysis show that both of the critical cross sections associated with the conceptual <br />geometry of the LRP and proposed Preparation Plant facility have adequate factors of safety for static and <br />dynamic conditions. This assumes a conceptual uniformly distributed load of 4,000 psf across the proposed <br />footprint. Using these assumptions, no stabilization is required in the vicinity of the proposed Preparation <br />Plant facility in addition to the LRP itself. <br />Parametric Analysis <br />The critical slip surfaces in both cross sections described above are associated with relatively shallow slope <br />failures, but the slip surfaces do not intersect the proposed footprint of the Preparation Plant facility. To <br />further investigate the potential effects of the building load on the factor safety for both slopes, the <br />uniformly distributed load from the facility was gradually increased to 20,000 psf in a parametric study. As <br />shown in Figure 7, at Cross Section A, the factor of safety does not decrease for loads up to 20,000 psf. <br />The building load affects the factor of safety at Cross Section B when the building load exceeds 8,000 to <br />15,000 psf. Overall, even at a building load of 20,000 psf, which is considered much higher than the <br />anticipated foundation loads, the factor of safety for both cross sections in all cases is greater than 1.20 as <br />shown in Figure 7. Thus, the loads from the proposed Preparation Plant facility are not anticipated to <br />impact slope stability. <br />-5-