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As previously documented along the northeast wall, and as described in this report, <br />planar failures can occur when foliation planes that are intersected by two or more joints <br />daylight in the exposed highwall. The stereonet plots shown for the northeast wall <br />(Figure 12) and the northwest wall (Figure 13) indicate a possibility for planar failure <br />along the foliation plane F-1. Planar failure can occur because the dip direction of the <br />F-1 plane can daylight into the slope face and the trend of the line of intersection formed <br />by F-1 and P-2 can act as a releasing surface. In addition, based on the stereonet <br />plots, intersections between discontinuities F-1 and P-2 and F-1 and P-3 potentially <br />exist, and the plunge line of each of the intersections will fall very close to or within the <br />daylighting envelope and at an inclination approximately equal to the angle of friction. <br />For the 2004 analysis (LF&A, 2004), the long-term impact of foliation F-1 on the stability <br />of both the northeast and northwest walls was further investigated using discontinuity <br />data that include elevation information for the foliation orientation. These data were <br />plotted on a chart showing dip angle in degrees versus elevation in feet (for chart see <br />LF&A, 2004). The results resulted in an increase in the number of daylighting foliation <br />planes that start at an elevation of 6,325 feet and continue with increased frequency to <br />below the planned final pit elevation. Due to the possibility of a lower friction angle <br />along the foliation plane (as low as 5°, average 28°) as determined from the 2003 <br />Geotechnical Study (L&A, 2003), the potential exists for future instabilities to occur on <br />the north walls as the pit is excavated to its final depth. These shallow dipping <br />discontinuities along the foliation can have a significant impact on the stability of the <br />north wall and should be monitored closely as excavation progresses. In addition, as <br />discussed in the previous section, an east-west striking unnamed fault zone is mapped <br />in the northwest corner of the main pit. With the combination of faulting and <br />discontinuities on the north walls, the potential impact on the slope stability should be <br />closely monitored as mining continues. <br />5.2.3 West Walls <br />No major stability issues currently exist for the west walls of the main pit of the quarry. <br />Previous analysis indicated that the west highwalls have approximately the optimum <br />-16-