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RULE 6.5: GEOTECHNICAL STABILITY EXHIBIT <br /> There are no known geologic hazards on the proposed site. Based on a slope stability analysis, <br /> buildings or other structures within 200' of the Siskin Green Pit mining area will not be affected <br /> by mining excavation. Sufficient buffers will be maintained to neighboring property lines. Maps <br /> C-2 and F-1 shows these buffers. Map C-3 shows the mining and reclamation slopes of the <br /> mine. The final reclamation condition will consist of benched rhyolite backfilled with broken rock, <br /> crushed rock, and overburden. <br /> The material properties are derived from Table 2.5 in the SME Mining Reference Handbook', as <br /> there is no site-specific sample 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 hard rock bench is rhyolite, which is best classified as a hard igneous rock with <br /> an internal friction angle of 35 degrees and cohesion of at least 720,000 lb/ft2.The backfill <br /> material is best classified as sand and gravel with a mixed grain size. From the SME table, sand <br /> and gravel with a mixed grain size has an internal angle of friction of 45 degrees and no <br /> cohesion. A layer of overburden/topsoil lies atop of the backfill. It is described loose sand with a <br /> mixed grain size which has an internal angle of friction of 34 degrees and no cohesion. <br /> The final reclamation condition was analyzed using Bishop's Method of Slices in GALENA <br /> software. The slopes are derived from Map C-3: benched hard rock with backfill and topsoil atop <br /> of it. <br /> 1 . Reclamation Slopes <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 Siskin Green Pit 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. Since the mining and reclamation plan is consistent all the way <br /> around the pit, a single slope stability analysis will suffice. Figure GS-1 shows the slopes <br /> evaluated in GALENA: the final rock benches backfilled and topsoiled for reclamation. <br /> The lowest factor of safety failure circle for the slope will be contained on a given bench. <br /> Therefore, the analyses starts with the failure circle on the top bench as the initial condition. <br /> From the initial condition the Bishop's Method of Slices iterates to find the lowest factor of <br /> safety. Figure GS-2 shows a sequence of these failure circles and associated FOS. The green <br /> arcs have FOS >= 1.5, the yellow have FOS = 1.38 to 1.5, and the red arc is the lowest FOS at <br /> 1.38. <br /> 1 Original source: Hoek and Bray 1977 <br /> Siskin <br /> August 2023 1 l.e��icl:i .assokiates <br />