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GEOTECHNICAL STABILITY EXHIBIT <br /> There are no buildings or any structures outside the permit area which could be affected by the <br /> excavation. A minimum 30 foot buffer will be maintained from the property boundary line to all <br /> new excavations. <br /> Mining onsite consists exclusively of mining the historic dredge tailings. Reclamation of the site <br /> will consist of regrading any remaining dredge pile slope to the 3H:1 V slope. All completely <br /> mined out dredge areas will be flat ground, topsoiled and seeded. Therefore, the permanent <br /> slope of regraded dredge piles in reclamation is evaluated for stability. <br /> 1 . Dredge mining <br /> The dredge piles are processed glacial and alluvial rock from historic placer gold mining, making <br /> them relatively clean of finer silts. The existing piles have shown long term stability (>50 years) <br /> at 1 HA V slopes. The reclaimed slopes at this stage will be 3H:1 V. <br /> From Table 2.5 in the SME Mining Reference Handbook', the dredge material is best classified <br /> as sand and gravel, mixed grain size. This material has an internal angle of friction of <br /> approximately 45 degrees and no cohesion. <br /> The Factor of Safety (FOS) for a (3H:1 V) 18.4 degree slope in sand and gravel with an <br /> assumed internal angle of friction of 45 degrees can be approximated by ignoring the cohesion <br /> component of the stability and simply evaluating the internal angle of friction as follows: <br /> FOS <br /> Tangent of Internal Angle of Friction <br /> = <br /> Tangent of Actual Angle of Failure Surface <br /> tan 45 <br /> FOS = 3.0 <br /> tan 18.4 <br /> 2. Conclusion <br /> The factor of safety is well above the minimum of 1.5 for permanent conditions. <br /> DODO <br /> f() 14 21 <br /> S�ONA1. <br /> 1 Original source: Houk and Bray 1977 <br />