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Blue Pit 112 Permit Amendment <br />The Factor of Safety (FOS) for gravel with a 20 degree slope in GC classified material with an <br />assumed internal angle of friction of 34 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 />Tangent of Actual Angle of Failure Surface <br />Tan 34° .67 <br />FOS = _ = 2.0 <br />Tan 20° .36 <br />This factor of safety far exceeds the normal long term safety factor of 1.3, therefore the plan of <br />extraction, as presented in Figure 4-502.C(6)A, is acceptable. In addition, the exposed i.5H:iV gravel <br />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 3H:1V. The backfilled <br />material will consist of overburden from previously excavated areas or reject fines, which is similar <br />to the overburden. <br />I, Greg Lewicki, P.E., with over 28 year of experience in mine slope safety analysis in Colorado, <br />certify that the mine plan and reclamation plan presented in this application will lead to stable <br />slopes during and after mining and that there is no realistic threat of failure or to the stability of <br />any structures outside of the permit area. <br />Greg Lewicki, P.E. <br />P.E. # 20335 <br />Da <br />----------------------------- -------- - ------------ -- ------ ----- Blue Pit Pit May 2014 U-3 <br />