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Christopher Schmitz June 2, 2014 <br /> Climax Molybdenum Company 3 1402712 001 TM01 RevO <br /> ■ Operational scenario: <br /> • Minimum allowable static factor of safety is 1.4 <br /> • Minimum allowable seismic factor of safety is >_1.0 <br /> • Operational basis earthquake (OBE) peak ground acceleration (PGA) is 0.06 g <br /> (representing the 1-in-475-years event) <br /> 3.0 METHODS AND ASSUMPTIONS <br /> ■ Because the ultimate OSF configuration remains unchanged from Golder's 2012 <br /> evaluation, stability of the interim OSF configuration was evaluated under operational <br /> conditions only (i.e., post-closure stability was not considered, as the interim OSF <br /> configuration will not exist at closure). <br /> ■ For consistency with previous work, cross sections for this analysis were developed <br /> along the same alignments used in the OSF design report (Golder 2012). The interim <br /> OSF plan only influences stability along cross-sections C and D. Therefore, this analysis <br /> only considers stability along these two sections. <br /> ■ Primary stability analyses were performed with RocScience's 2-D limit equilibrium <br /> program, Slide 6.0. Factors of safety were computed based on Spencer's Method of <br /> Slices (Spencer 1967). <br /> ■ Both circular and non-circular(block)failure surfaces were evaluated. <br /> ■ Since approximately 30 percent of the OSF is expected to be composed of overburden <br /> derived from the Minturn Formation shale, siltstone, and sandstone, two strength <br /> envelopes were used for the overburden material: <br /> • Envelope 1: A conservative best approximation of the overburden material strength <br /> based on the residual strength obtained from two large-scale direct shear tests <br /> performed on representative samples of overburden. <br /> • Envelope 2: A "lower bound" strength envelope defined by the Leps (1971) low <br /> strength curve. Golder considers this envelope to represent a lower bound strength <br /> for the OSF suitable for evaluating the stability of the OSF in the event that a <br /> significant contiguous portion of the facility is constructed from sedimentary <br /> overburden. <br /> ■ Both deep and shallow failure surfaces were investigated. However, surficial veneer <br /> (infinite slope) slip surfaces were excluded from the results. Critical failure surfaces were <br /> constrained to a minimum depth of 15 feet. <br /> ■ Veneer failures on the face of the dump become more common for the operational OSF <br /> configuration when the lower bound strength envelope is used. Thus, Golder (2012) <br /> previously recommended that overburden material derived from the higher-strength <br /> igneous or metamorphic rocks will be placed within 50 feet of the ultimate face of the <br /> OSF. <br /> ■ The geometry, piezometric assumptions, and material parameters were obtained based <br /> on the field investigation performed in October and November 2011. <br /> ■ Design material parameters were determined based on a series of geotechnical <br /> laboratory tests conducted by Golder on samples of native soils (Lincoln Porphyry, <br /> Minturn Formation, and Glacial Till) and mine materials (overburden and tailings). These <br /> soil parameters are described in Section 4.0. <br /> ■ Residual strength soil parameters were used for the static stability analysis wherever <br /> applicable. <br /> -t - <br /> - Golder <br /> I:\14\1402712\0100\0122\001 TM01 RevO\1402712 001 TM01 RM ClimaxMolyOSFStabilityAnalysis 02JUN14.docx `V- Associates <br />