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RULE 6.5: GEOTECHNICAL STABILITY EXHIBIT <br /> Colorado Geologic Survey mapping for the Pit Number One shows granodiorite bedrock <br /> underlays the gravel deposit onsite'. There are no known geologic hazards on the proposed <br /> site. Based on a slope stability analysis, buildings or other structures within 200-ft of the Pit <br /> Number One affected area will not be affected by mining excavation. Sufficient buffers will be <br /> maintained between the slope crest and the permit boundary. A standard slope was analyzed <br /> for stability to determine if there was offsite impact within 25-ft of the mining area. <br /> The material properties are derived from Table 2.5 in the SME Mining Reference Handbook2, as <br /> there is no site-specific strength data of the material available. Therefore, all materials are <br /> matched to a classification from this table that best matches the materials in terms of <br /> description. The native alluvial material is best classified as sand and gravel with a mixed grain <br /> size. A summary of the material properties can be seen in Table GS-1. <br /> Table GS-1. Material Properties <br /> Material Unit Weight(lbs/ft) Cohesion Friction Angle <br /> Sand and gravel,mixed grain size 115 0 45 <br /> The final reclamation (3H:1V) slope was analyzed. <br /> 1 . Methodology <br /> Factor of Safety is expressed in terms of strength divided by stress as a ratio. It is arrived at by <br /> an iterative computer process where a slope failure is assumed, the strength and stress of that <br /> slope failure are calculated, and those values are compared to determine a lowest factor of <br /> safety. In the case of the Pit Number One slope stability analysis, the Bishop's Method of Slices <br /> was the iterative calculation used, and the software GALENA was used to model slopes and <br /> calculate the factor of safety. One slope (see Figure GS-1) was analyzed to look at the factor of <br /> safety. <br /> 2. Analyzed Slopes — Active Mining & Reclamation Slopes <br /> The Active Mining slope is 2H:1V and a maximum 20-ft tall. This slope will be maintained <br /> throughout the active highwall, before being backsloped to the final reclaimed slope. <br /> 1 Geologic Map of the Ponchas Pass area, Chaffee, Fremont, and Saguache Counties, Colorado. 2019. <br /> 2 Original source: Hoek and Bray 1977 <br /> Pit Number One GS-1 l.caicki& Associates <br /> April 2025 <br />