2012-02-28_REVISION - M1980244 (65)

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Cripple Creek & Victor Gold Mining Company Squaw Gulch Valley Leach Facility Design published shear strength data for rock fill materials (Leps, 1970), where the internal friction angles range between 39 to 50 degrees for similar -sized materials under similar normal stresses. Based on the results of the shear tests conducted on the Cresson ore and published data, an internal friction angle of 40 degrees is suitable for the stability analyses. The in -place bulk density of the material is modeled at 110 pcf, which is consistent with that submitted previously to the OMLR. Composite Liner. Interface shear strength testing performed as part of the design for the OSA consisted of SLF overlain by 80 -mil textured LLDPE liner (textured side down) overlain by DCF. Interface shear strength testing was performed for normal loads of 50, 100, 150, and 200 psi. The interface testing for these normal loads was used to define a linear relationship (friction angle and cohesion) between the normal loads calculated in the stability section slices and the corresponding shear strength. The SLF was compacted to 95 percent of the standard Proctor maximum dry density at 2 percent above the optimum moisture content. At large strain (45 mm), the residual interface shear strength had a friction angle of 23.5 degrees. At low stress, the failure surface developed between the geomembrane and the DCF. At higher stresses, the failure surface developed between the geomembrane and the SLF. No further interface testing was conducted for the PSSA composite liner systems because these materials were already tested as part of the Cresson Project VLF design. Interface shear strength test results for the Cresson Project are presented in Appendix B.6. Foundation Material. For the stability analyses, the foundation material shear strength was modeled with an angle of internal friction of 40 degrees and no cohesion, which represents either a bedrock foundation or a granular fill foundation. The results of the geotechnical investigation indicate the foundation of the VLF will primarily be constructed in bedrock. This is consistent with what was used in Amendment No. 9 to represent the shear strength of the foundation. PSSA Embankment Fill. The PSSA embankment will be constructed using structural fill and other suitable coarse fill. For the stability analyses, the PSSA embankment fill shear strength was modeled with an angle of internal friction of 38 degrees and no cohesion. Piezometric Data. The piezometric head was modeled as 1 foot above and parallel to the lined surface, which is consistent with the conditions used in Amendment Nos. 6, 7, 8, and 9 (CC&V 1993a, 1998, 2000, 2008). 5.1.3 Stability Results The maximum side slope of 1.6H:1 V was calculated as part of an infinite slope analysis, which represents the steepest side slope that will still provide a pseudo- static FOS of 1.0 or greater for surface raveling of ore material during a 0.14g seismic event. Infinite slope stability analyses are presented in Appendix E.1. Based on this analysis, Project No.: 74201125G0 Page 29 1 September 2011 amec0