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The Factor of Safety(FOS) for sand backfill with a(3H:IV) 18.4 degree slope in SM classified <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 /> FOS = Tan 34' _ 0.6745 _ 2.0 <br /> Tan 18.40 0.3326 <br /> Ignoring cohesion in this scenario is done to accommodate a range of saturation conditions. <br /> Installing SM classified material at no steeper than 3H:1V ensures that the slope is stable regardless <br /> of the water table level. <br /> 2.3 Conclusion <br /> The factor of safety in both scenarios is 2.0,well above the minimum of 1.5 for permanent <br /> conditions. <br /> Ben Langenfeld, P.E. <br /> P.E.# 0047151 <br /> Date: <br /> 5 Mile Pit March 2016 GEO-4 <br />