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• SMITH WILLIAMS CONSULTANTS, INC. <br />reclaimed slopes graded at 2.5 horizontal (H):1 vertical (V). During operations, the OSA slopes <br />may vary from angle of repose to 2.SH:1 V, or flatter, depending on how the OSA is developed. <br />The following material properties were used in the models: <br />Overburden Material. The overburden material is modeled as a coarse rockfill, with an <br />average bulk unit weight of 125 pounds per cubic foot (pcf). The rockfill is assumed to have a <br />shear strength defined as a linear Mohr-Coulomb envelope, with an internal angle of friction of <br />39 degrees and zero cohesion. These values are consistent with that used in previous <br />Amendments. <br />Foundat-on Material. For the stability analyses, the foundation of the OSAs was <br />conservatively modeled as soil, even though some areas will have bedrock at or very near the <br />ground surface. The foundation soil was modeled with a bulk unit weight of 110 pcf. The shear <br />strength of the foundation soils was based on test data presented in previous Amendments. <br />Direct shear tests conducted on foundation soils excavated within the limits of the SGOSA <br />yielded a residual friction angle of between 28.2 degrees to 29.5 degrees. Based on these results, <br />• a friction angle of 29 degrees was selected to represent the strength of the foundation materials <br />for both the SGOSAE and ECOSA foundations. The ECOSA soils are considered very similar <br />to the SGOSA soils based on grain size and Atterberg limits. <br />3.1.2 Stability Results <br />The results of the stability analyses for the SGOSAE and ECOSA are presented in Appendix A, <br />and summarized in Table 1. As presented in Table 1, the stability sections indicate that the static <br />FOS values are 1.5 or greater, and pseudo-static FOS values are 1.0 or greater for design <br />acceleration of 0.08g. It is important to note that, as in previous stability analyses presented and <br />approved for the Cresson Mine, the FOS values reported represent the reclamation side slopes of <br />2.SH:1V. During operations, the OSA side slopes may vary between angle of repose to 2.SH:1V, <br />or flatter. <br />.7 <br />S:\PROJECTS\t 125C CC&V CRESSON OSA\H2 -DESIGN\OSA STABILITY FINAL REPORT V3.DOC 4 <br />