2023-10-31_REVISION - M1973021 (15)

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Geotechnical Stability Exhibit �� Engineering Evaluation of Highwall Design for the South Quarry of the Morrison Quarry laboratory direct shear testing of rock samples were utilized to determine a design friction angle for the competent and talc-gneiss materials. An average of competent material direct shear values was utilized to select the design friction angle of 27 degrees and the minimum tested value of 14 degrees was conservatively selected as the design friction angle for the talc-gneiss material. An average slope angle of 85 degrees was utilized for bench slopes, with a typical lateral limit of 35 degrees to account for variation of slope directions, and kinematics were analyzed for North, East, South, and West slope directions and for both competent material and talc-gneiss. The results of the kinematics analysis is summarized in Table 10 below. Table 10— Distribution of Kinematic Analyses Results Distribution of Kinematic Analyses Results Material North- East-Facing South-Facing West-Facing Type Failure Mode Facing Slopes Slopes Slopes Slopes Planar Sliding 9.95% 13.38% 13.21% 11.66% Wedge 14.42% 19.20% 19.10% 15.27% Competent Sliding Material Flexural 12.86% 9.95% 9.09% 13.21% Toppling Direct 18.71% 14.59% 12.21% 14.06% Toppling Planar Sliding 13.04% 16.98% 18.01% 14.58% Wedge 22.86% 29.54% 30.77% 24.98% Talc Sliding Gneiss Flexural 16.47% 13.55% 11.15% 15.61% Toppling Direct 18.71% 14.59% 12.21% 14.06% Toppling The results of the kinematic analyses provide an indication of the potential and type of localized failures in the exposed benches and highwalls of the South Quarry. The stereonet projections give an indication of potential instability by calculating the number of discontinuities (or combination of discontinuities) that could possibly result in a failure for a given slope configuration. The number of kinematically possible failure surfaces are divided by the number of surfaces which would not likely result in a failure, and the results are expressed as a percentage. The results thusly give an indication of possible failure modes and their respective likelihoods relative to each other and are not intended to provide a factor of safety. This analysis method also does not account for joint and foliation shear strengths within the rock mass. Detailed stereonets and kinematic results are provided in Appendix C, Calculations. Annual reporting and field inspections indicate that the South Quarry highwall is generally stable in regards to large scale global stability. The heavily fractured nature of the rock within the South Quarry tends to fail in small and localized instabilities that are considered typical for mining operations. Observing the kinematics distribution shows that wedge failures are the most likely, particularly in south and east-facing benches, which is consistent with noted field evaluations. May 2023 1 25