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Cripple Creek&Victor Gold Mine <br /> Valley Leach Facility Expansions ■ <br /> Detailed Design for Permitting <br /> NewFields Project No.475.0106.064 1111 <br /> March 2024 <br /> 5.1.2. Design Ground Motions <br /> To assess the stability of slopes during seismic loading, a pseudostatic approach was used where <br /> the potential slide mass is subjected to an additional, destabilizing horizontal force which <br /> represents the effect of earthquake motions and is directly related to the PGA. The seismic force <br /> is the weight of the slide mass multiplied by a horizontal pseudostatic earthquake coefficient(kH), <br /> which is commonly related to the peak ground acceleration by an acceleration multiplier. <br /> Referenced values of the acceleration multiplier range from approximately 0.2 to 0.8, with 0.5 <br /> being a commonly applied value (Duncan and Wright, 2005). <br /> For the current evaluation,the simplified methodology proposed by Bray and Macedo(2019)was <br /> used to estimate the kH value based on 6-inches of allowable deformation,the design earthquake <br /> magnitude for the 1 in 2,475 years Annual Exceedance Probability event, and the natural <br /> frequency of the failure mass. The estimated kH value is a function of presumptive shear wave <br /> velocity through the ore and embankment fill and use of either the mean or modal earthquake <br /> magnitude. The methodology resulted in a kH value less than half the PGA, and for the current <br /> analysis a kH value of half the PGA (0.07g)was conservatively applied. <br /> • 5.1.3. Material Properties <br /> The material properties used in the stability analysis are based on available laboratory test data <br /> and our understanding of general site conditions.The materials are summarized in Table 5.1 and <br /> discussed below. <br /> Table 5.1—Stability Evaluation Material Properties <br /> Power Curve Mohr—Coulomb <br /> Moist Unit <br /> Material Wei ht z —A•anB 'r = c' + a tan(p' <br /> g(psf) A B c. <br /> (deg) in (psf) <br /> Ore(Existing and Proposed) 120 3.963 0.841 - - <br /> Composite Liner Interface 120 1.169 0.886 - - <br /> Pit Backfill and Fill 120 35 0 <br /> Foundation(Sand and Gravel) 125 - - 32 0 <br /> Foundation (Bedrock) 150 - - 45 0 <br /> Ore: Direct shear tests were completed on different mixtures or virgin ore materials and failure <br /> was chosen at 15 percent strain (NewFields, 2019, 2023). A non-linear power curve was <br /> considered the most representative failure envelope and plots slightly higher at low stress and <br /> • slightly lower at high stress compared to average rockfill characteristics as shown on Figure 5.1. <br /> Page 18 <br />