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J.E. Stover & Associates <br />Terracon Project No. 65995058 <br />June 3, 1999 <br />as a conservative analysis, we have included an estimated a phreatic surface in the stability <br />evaluations for maximum high water level. For that case, the analyses include: <br />Case IV: Rapid Drawdown from full pond stage <br />All of the stability analyses have been completed for static conditions. No earthquake loading <br />has been considered in the models. <br />Analytical Approach: Stability analyses were performed using the computer program <br />PCSTABL6H developed by the Purdue University. PCSTABL6H utilizes algorithms for the <br />Modified Bishop method of slices for circular slip surfaces and modified Janbu techniques for <br />irregular surfaces and for translation of active-passive block failure surfaces. Modified Bishop <br />analyses were performed on all cross sections using interior and exterior embankments <br />slopes, where applicable. <br />For each analysis, 400 potential failure surfaces for each cross section were analyzed. <br />Initiation points and termination limits of each set of failure surfaces were adjusted in order that <br />the most critical trial surface was contained within the bounds set by these parameters. <br />Detailed results of the stability calculations are included in Appendix A. The graphical <br />summaries include figures showing the locations of each of the 400 trial failure surfaces <br />analyzed and figures showing the ten failure surfaces examined with the lowest calculated <br />factors of safety for each condition. <br />For the Transfer Station Bench, limiting boundaries were included in the cross section to <br />simulate the presence of underlying bedrock. These boundary conditions were used to deflect <br />all potential failure surfaces analyzed in an upward direction. Consequently, all failure <br />surfaces analyzed for this cross section were contained within the soils lying above the <br />estimated level of bedrock in the model. <br />Where applicable in the analyses, live load surcharge of 500 psf was used to simulate <br />anticipated mine traffic on haul roads that will be located above the proposed slopes. For the <br />coal stockpile pad, a live load surcharge of 5000 psf was used to simulate coal stockpile <br />loading on proposed fill embankments. The stability of the coal within the stockpile has not <br />been considered in the analyses. <br />Results of the stability analyses for each case and the corresponding calculated factors of <br />• safety are summarized in Table 1. <br />7 <br />