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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 Lockhart Pit mining area will not be affected by <br /> mining excavation. Sufficient buffers will be maintained to neighboring property lines. Maps C-2 <br /> and F-1 shows these buffers. Map C-3 shows the mining and reclamation slopes of the mine. A <br /> standardized mining and reclaimed slope was analyzed for stability based on the maximum <br /> depth of sand and gravel. No overburden is anticipated to be found onsite. <br /> The material properties are derived from Table 2.5 in the SME Mining Reference Handbook3, 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 native alluvial material is best classified as sand and gravel with a mixed grain <br /> size. From the SME table, sand and gravel with a mixed grain size has an internal angle of <br /> friction of 45 degrees and no cohesion. <br /> The final mining (2HAV), final reclamation (3HAV), and active highwall (near vertical) slopes <br /> were analyzed. Mining will be conducted at the active highwall angle until the highwall has <br /> reached the half-way point of the final mining slope. Then the vertical active highwall slope will <br /> be knocked down to the final mining slope of 2H:1 V. Then, the mining slope at 2H:1 V it will be <br /> backfilled with to the final reclamation slope of 3H:1 V. <br /> 1 . Mining and 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 Lockhart Pit slope stability analysis, the Bishop's Method of Slices was <br /> the iterative calculation used, and the software GALENA was used to model slopes and <br /> calculate the factor of safety. Since both pods onsite will be mining and reclaiming the same <br /> deposit a single, standardized slope can be used to evaluate the slope stability at the Lockhart <br /> Pit. <br /> Figure GS-1 shows the standardized slopes evaluated in GALENA: the full mining slope and the <br /> permanent reclaimed slope. <br /> The lowest factor of safety for permanent slopes was 3.03 at Final Reclamation. The distance <br /> between the closest slope edge or failure circle and the nearest structure is shown Table GS-1. <br /> GALENA data tables and analysis result figures are attached as Appendix GS-1. <br /> 3 Original source:Houk and Bray 1977 <br /> Lockhart Pit GS-1 Lewicki&Associates <br /> March 2024 <br />