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Geotechnical Stability Exhibit ��� <br /> Engineering Evaluation of Highwall Design for the South Quarry of the Morrison Quarry <br /> 6 Quarry Geometry Recommendations <br /> 6.1 Kinematic Stability Results <br /> In areas surveyed at the Morrison Quarry by HDR personnel, conditions that indicate the <br /> potential for large-scale slope failures were not apparent. For competent material, there is a low <br /> probability of large wedge or toppling failures due to the joint and foliation orientation observed <br /> in the headwalls. Additionally, there is a low probability of large plane failures along foliation <br /> surfaces that can occur when the foliation surface dips into the highwall face at a high angle. <br /> Planar failure is at its highest risk in East and South facing slopes. Wedge failure is at its <br /> highest risk in east-facing slopes. Toppling is at its highest risk in north-facing slopes. For talc- <br /> gneiss material, there is an overall higher risk of failure. Planar and wedge failure are at its <br /> highest risk in south-facing slopes. Toppling is at its highest risk in north-facing slopes. In <br /> general, based on previous site evaluations and the history of the mine, it is expected that the <br /> high degree of fracturing and weathering will cause smaller scale localized failures that are <br /> considered typical to this type of mine. <br /> 6.2 Slope Stability Results <br /> The results of the slope stability analyses generally indicate that factors of safety approach the <br /> critical 1.25 when consecutive benches of talc-gneiss are encountered. Based on the geologic <br /> model, the worst case scenario for the presence of the less stable, talc-gneiss bedrock, <br /> encompasses three (3) consecutive 40/40 benches. This condition was most critical at the XS- <br /> East (200) section, proposed left, as referenced in Table 11. If more than 3 consecutive <br /> benches of talc-gneiss are encountered, this reduces the factor of safety below the required <br /> 1.25. Therefore, the proposed geometry of 40/40 benches from El. 6600' to El. 6200' is <br /> acceptable however the presence of talc-gneiss in the mine should be monitored closely as part <br /> of the annual geotechnical addendum and an additional stability evaluation should be performed <br /> if 4 or more consecutive benches of talc-gneiss are encountered. At this time, based on the <br /> geologic model created by HDR it is not expected that 4 or more consecutive benches of talc- <br /> gneiss will be encountered in the South Quarry during excavations from El. 6600' to El. 6200'. <br /> May 2023 1 29 <br />