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6.2.2 North Walls <br />Similar to the previous LF&A annual reports, the north wall has been subdivided <br />into two separate slopes for analysis: the northeast and the northwest wall. The <br />instabilities observed in the eastern section of the wall and the differing slope <br />orientations necessitated the distinction between the two slopes. To take into <br />account the shallower slope angle of the past three benches as well as the final <br />mine plan design, a 35° dip angle for the slope was used in the analysis of each <br />' of the north walls. <br />L As previously documented along the northeast wall, and as described in this <br /> report, planar failures can occur when foliation planes that are intersected by two <br /> or more joints daylight in the exposed highwall. The stereonet plots shown for <br /> the northeast wall (Figure 11) and the northwest wall (Figure 12) indicate a <br /> possibility for planar failure along the foliation plane F-1. Planar failure can occur <br /> because the dip direction of the F-1 plane falls between the dip direction of the <br />' slope face and the trend of the line of intersection formed by F-1 and P-2. In <br /> addition, based on the stereonet plots, intersections between discontinuities F-1 <br /> and P-2 and F-1 and P-3 will potentially occur, and each of the intersections will <br /> fall very close to or within the daylighting envelope. <br /> <br /> For the 2004 analysis (LF&A, 2004), the long-term impact of foliation F-1 on the <br />' stability of both the northeast and northwest walls was further investigated using <br /> discontinuity data that include elevation information for the foliation orientation. <br /> These data were plotted on a chart showing dip angle in degrees versus <br /> elevation in feet (for chart see LF&A, 2004). The results indicate an increase in <br /> the number of daylighting foliation planes that start at an elevation of 6,325 feet <br /> and continue with increased frequency to below the planned final pit elevation. <br /> This indicates that the potential exists for future instabilities to occur on the north <br /> 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 <br /> the north wall and should be monitored closely as excavation progresses. In <br />' -20-