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Case 2 - North of Access Road <br />Overburden <br />The Factor of Safety (FOS) for overburden with a 18.2 degree slope in ML-CL classified <br />material with an assumed internal angle of friction of thirty-four degrees can be approximated by <br />ignoring the cohesion component of the stability and simply evaluating the internal angle of <br />friction as follows: <br />FOS = <br />Tangent of Internal Angle of Friction <br />Tangent of Actual Angle of Failure Surface <br />Tan 32° .6249 <br />FOS = _ = 1.90 <br />Tan 18.2° .3288 <br />Gravel <br />The Factor of Safety (FOS) for gravel with a 18.2 degree slope in GC classified material with an <br />assumed internal angle of friction of thirty-four degrees can be approximated by ignoring the <br />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 />= <br />Tangent of Actual Angle of Failure Surface <br />Tan 34° .6745 <br />FOS = _ = 2.05 <br />Tan 18.2° .3288 <br />Both of these factors of safety far exceed the normal long term safety factor of 1.3, therefore, the <br />plan of extraction, as presented in Figure U-1, is acceptable. In addition, the exposed vertical <br />gravel slopes will only be present for a short period of time, since the mine will be conducting <br />contemporaneous reclamation. These backfilled slopes are at a slope of 2H:1 V. The backfilled <br />material will consist of overburden from previously excavated areas or reject fines, which is <br />similar to the overburden. Both of these materials will be backfilled to 90% of the maximum dry <br />Cugnini Pit, November 2009 U-3