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`7 <br />~r <br /> <br />Mai nCressonSlopeEvaluation <br />~~~R~~~~~ ~~~~~~ <br />AdrianBrown <br />8. CONCLUSION <br />The Main Cresson Mine is located in strong, dry, blocky, highly frictional rock. Slopes in this area are <br />generally expected to be stable. Evaluation of the stability of the rock slopes produces the following <br />conclusions: <br />1. The overall slope of the mine walls is not controlled by overall rock strength, but by bench <br />design and ore distribution considerations. <br />2. On the east wall of the mine, the overall slope can be 60°, to take advantage of the rock <br />strength and mine conditions. <br />3. Two overall bench designs have been evaluated: triple 25 foot benches, with a 25 foot catch <br />bench, and quadruple 25 foot benches, with a 34 foot catch bench. In each case the design <br />uses 25 foot high faces at 80° face slope, separated by 2 foot setbacks. Both systems are <br />stable; the quadruple bench development creates approximately 33% more catch capacity. <br />4. Fora 700 foot high, 60° slope the minimum factor of safety against overall failure is T.33 <br />assuming the formation of a kink band, and 3.6 in the absence of kink or shear band formation <br />5. Very limited sapling of rock is expected on the slope; accordingly, minimal catch bench <br />• capacity is needed. The capacity of the benches in the proposed design is 11 cubic yards per <br />foot of bench for the triple bench system, and 19 cubic yards per foot of bench in the quad <br />bench system. <br />• <br />1385D.980612 56 <br />