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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 Delta Paving Gravel Pit affected area will not be <br /> affected by mining excavation. Sufficient buffers will be maintained to neighboring property <br /> lines. Maps C-2 and F-1 shows these buffers. Map C-3 shows the mining and reclamation <br /> slopes of the mine. A standard slope in Phase 4 was analyzed for stability as it is the closest to <br /> offsite structures like fences and the state highway. <br /> The material properties are derived from Table 2.5 in the SME Mining Reference Handbook' <br /> and Table 3.1 in Stability Analysis of Earth Slopes (Huang)2, as there is no site-specific sample <br /> data of the material available. Therefore, all materials are matched to a classification from this <br /> table that best matches the materials in terms of description. The native alluvial material is best <br /> classified as sand and gravel with a mixed grain size. From the SME table, sand and gravel with <br /> a mixed grain size has an internal angle of friction of 45 degrees and no cohesion. A layer of <br /> overburden/topsoil lies atop of the sand and gravel. It is described in the soil survey for this area <br /> as silty clay loam. This best matches the description for ML-CL soils (mixture of inorganic silts <br /> and clays) from Huang which has an internal angle of friction of 32 degrees and modest <br /> cohesion. <br /> The final mining (2H:1V), final reclamation (3H:1V), 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:1V. Then it will be backfilled with <br /> overburden/topsoil to the final reclamation slope of 3H:1 V. <br /> A surcharge distributed load representing the topsoil berm placed along the west end of the <br /> slope has been included in the GALENA analysis. <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 Delta Paving 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 closest to major structures (see Figure GS-1) was <br /> I Original source: Houk and Bray 1977 <br /> 2 Source: Huang, Y. Stability Analysis of Earth Slopes. 1983.Table 3.1 Average Effective Shear Strength of <br /> Compacted Soils. <br /> Delta Paving GS-1 Lewicki&Associates <br /> December 2020 <br />