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2. Scenario 2—Non-dredge mining <br /> Once mining is taking place below the bottom of the dredge piles,the final reclamation plan will shift <br /> to involve backfilling of the final mine slopes to 3H:1 V with fines from processing. This backfill will <br /> be similar to the native material that it is placed upon. The difference will be the lack of gravel and <br /> cobbles in the backfill material. <br /> From Table 2.5 in the SME Mining Reference Handbook2, the backfill is best classified as loose <br /> sand, mixed grain size. This material has an internal angle of friction of approximately 34 degrees <br /> and no cohesion. <br /> The Factor of Safety(FOS) for sand and gravel with a(3H:IV) 18.4 degree slope in loose sand <br /> material with an assumed internal angle of friction of 34 degrees can be approximated by ignoring <br /> the cohesion component of the stability and simply evaluating the internal angle of friction as <br /> follows: <br /> FOS = Tangent of Internal Angle of Friction <br /> Tangent of Actual Angle of Failure Surface <br /> Tan 34' 0.6745 <br /> FOS = — = 2.02 <br /> Tan 18.40 0.3326 <br /> 2 Original source:Houk and Bray 1977 <br /> Trout Valley Ranch November 2016 GEO-2 <br />