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CESARE,INC. <br /> N =0 <br /> EXHIBIT 4. Stereonet of the fracture data for the portion of the high wall that was <br /> accessible. Rockfall hazards typically come from the intersection of the fracture planes <br /> and the cut face. In this case,they are not intersecting in such a way as to create a large <br /> wedge that could slide or topple from the cut face. <br /> 3.3 OTHER OBERVATIONS <br /> The rhyolite core stones pose a rock rolling hazard as the quarry operation moves rock from under <br /> and around the spherical stones. These stones will roll farther and with greater energy than the <br /> smaller angular blocks of obsidian. Excavation around these stones should either place them carefully, <br /> blast them apart, or allow them a free path to roll to the bottom of the slope. This seems to be the <br /> current operating procedure in the quarry. <br /> 4. CONCLUSIONS AND RECOMMENDATIONS <br /> The CMTTS engineering geologist concluded that high wall at the obsidian quarry operation remains <br /> stable due to the strike of the high wall not creating a wedge failure from the persistent fracture sets. <br /> Although the rock mass rating of the rock in the high wall indicates a low stand up time, the benches <br /> and waste rock buttresses add stability to the lower parts of the slope. The operation of the quarry <br /> is currently creating stable slopes along the high wall. The desired high wall and bench width <br /> configuration of 30:15 (H:W) is close to what is currently operational, and this slope/bench <br /> configuration should not change the overall slope stability of the quarry. <br /> As operations continue along the east-west strike of the quarry face and new high wall areas are <br /> blasted and excavated, CMTTS's recommendation is to update the high wall control plan as new <br /> areas are uncovered that may have different joint sets or more highly fractured rock faces. <br /> 22.6084 Obsidian Quarry Slope Consultation Letter 06.29.22 5 <br />