2013-05-10_REVISION - M1977193 (3)

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#6, showing all benches. In a sequence of repetitive geometry of likewise material, a planar surface projected for analytical process allows better processing and fewer multiple failure and Sarma block iterations required by the program. Comparing Bishop Simplified Method Analysis 2, Analysis 3, and Analysis 8 -I1 show circular and non - circular failure plane Multiple Stability Analysis results with a failure plane headwall progression well west of the highwall crest utilizing a critical seed starting point from the limit of the last failure plane. Factor of Safety results ranged between 1.35 and 1.40. Spencer - Wright Analysis were run for a number of non - circular failure plane scenarios including single bench, multiple bench, and total bench failure projections. Designated failure plane projections included secondary joint dip angles included (East dipping). Tension crack inputs were used in model input to address a tendency for development of negative forces at the base or sides of the failure plane. When perusing analytical results associated with Spencer - Wright analysis, a number of these results contain such notations, although the force identified is limited to the last slice at the top left of the failure plane, a relatively minor consideration regarding impact on analytic result. Spencer - Wright results show a wider range of FOS between 1.32 and 2.57, mostly grouped around 1.9. Sarma Method Analysis trials were performed and modeling of such proved to be more challenging in meeting input requirements to the model that did not result in excessive negative forces noted along base and side slices of the model. The Sarma methodology also utilizes the concept of a Critical Acceleration Factor (Kc) that must be greater than 0 for analytical validity. Several results met at least this requirement including a Multiple Stability Analysis for a Non - Circular Surface modeled to deeper elevations from the bench and shown as a 1:1 plane for analytical purposes. The Sarma runs that meet the basic results validity requirements are consistent and comparable to Spencer - Wright results for Non - Circular Surfaces. Factor of Safety results also proved to be comparable to other methods. Summary and Conclusions Application of the Galena Slope Stability Program utilizing rock parameters from materials sampled at this location have provided consistent analytical results showing a range of reasonable Factor of Safety assumptions for the final mine bench development proposed in this permit amendment proposal. Factor of Safety estimates are based on updated measurements of rock structure, foliation, jointing, and mining direction and include considerations for tension cracking, directional planes of potential weakness, and regional seismic force potential. Current highwall development confirms that the most stable bench configuration is created where foliation directions and the primary jointing system directions coincide, aligned generally within 10 degrees of the final highwall direction. Mining personnel will need to continue to mine along the preferred breaking plane as mining operations approach the final mine bench location at each elevation. Allowing the direction and dip of the foliation to guide the final highwall edge dynamic E