2008-04-15_REVISION - M1980244 (193)

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~~ MainCressonSlopeEvaluation Adrian6rown • 7.3 Bench Design 7.3.1 Triple Bench The current mining approach uses a triple benching method. The bench design to achieve the proposed 60° overall slope is as follows: Catch bench width ............................................................................... 26 ft Face slope ............................................................................................. 80° Face height .......................................................................................... 25 ft Number of faces between catch benches ................................................... 3 Face setback at crest ............................................................................. 2 ft Overall slope angle (three bench plus catch bench) ° ................................ 60 Catch capacity ............................................................ l l cuyd/ft (17 ton/ft) This design is illustrated in Figure 22. It should be noted that this design is generic, in that the actual bench geometry will be locally influenced by geology, structure, wall geometry, haul road location, blasting pattern and practices, drilling equipment, and other factors. The critical design requirements are that the overall slope be 60°, and that the catch bench be not less than 25 feet wide. In order to achieve • this objective, the horizontal distance from the crest of the upper catch bench to the toe of the slope on the lower catch bench should not be more than 17 feet. 7.3.2 Quadruple Bench Design An alternative method to obtain a 60° final slope, while maintaining a substantial catch capacity for the mine wall, is the use of a quadruple bench system, with the following design: Catch bench width ............................................................................ 32.7 ft Face slope ............................................................................................. 79° Face height .......................................................................................... 25 ft Number of beriches ................................................................................... 4 Face setback .......................................................................................... 2 ft Overall slope angle (three bench plus catch bench) ................................ 60° Catch capacity ............................................................18 cuyd/ft (28 ton/ft} This design is illustrated in Figure 23. It should again be noted that this design is generic, in that the actual bench geometry will be Locally influenced by geology, structure, wall geometry, haul road location, blasting pattern and practices, drilling equipment, and other factors. The main design requirements are that the overall slope be 60°, and that the catch bench be not less than 34 feet wide. In order to achieve this objective, the horizontal distance from the crest of the upper catch bench to the toe of the slope on the lower catch bench should not be more than 24 feet. • 1385D.980672 53