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<br />GHMXSIopeEvaluation <br />61'=6~+k63 <br />where: 61' =major principal effective stress at failure <br />63' =minor principal effective stress at failure <br />a~ = al' axis intercept of the tangent to the failure criterion at 63' = yH <br />k =slope of the tangent to the failure criterion at 63' = yH <br />From the k value, the Mohr-Coulomb parameters are computed: <br />~' = asin[(k-1)/(k+l )] <br />where: ~' =effective stress friction angle <br />c' =effective stress cohesion <br />6~ = 6i' axis intercept of the tangent to the failure criterion at 63' = yH <br />k =slope of the tangent to the failure criterion at 63' = yH <br />3.1.3 Circular Slope Failure Analysis <br />The analysis has been performed using the Mohr-Coulomb parameters derived by the method described <br />above. The parameters for the mine rock are computed for wall segments, and the rock mass parameters <br />• are computed for the stress conditions at the toe of the greatest height wall in the mine. The analysis was <br />performed by computing the dimensionless Hoek and Brown chart parameter: <br />c'/(yHtan~') <br />where: c' =effective stress cohesion of rockmass <br />~' =effective stress friction angle of rockmass <br />y =specific weight of the rockmass <br />H =height of wall <br />The ray for this parameter is drawn from the origin of the Hoek chart for a drained slope, and the value <br />of the cohesion parameter is found at the intersection with the slope angle traces presented on the graph. <br />The cohesion parameter is defined as: <br />where: C =cohesion parameter <br />c' =effective stress cohesion of rockmass <br />y =specific weight of the rockmass <br />H =height of wall <br />F =factor of safety <br />The factor of safety is computed from the cohesion parameter by rearrangement: <br /> <br />• <br />Report 1385E.20071126 <br />