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<br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />~l <br />CJ <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 />For the 2004 analysis, the long-term impact of foliation F-1 on the stability of <br />both the northeast and northwest walls was further investigated using the <br />discontinuity data collected that contains elevation information for the foliation <br />orientation. This data was plotted on a chart showing dip angle in degrees <br />versus elevation in feet (Figure 14). The plot indicated an increase in the <br />number of daylighting foliation planes that start at an elevation of 6,325 feet and <br />continue to below the planned final pit elevation. This indicates that the potential <br />exists for future instabilities to occur on the north walls as the pit is excavated to <br />its final depth. These shallow dipping discontinuities along the foliation can have <br />a significant impact on the stability of the north wall and should be monitored <br />closely as excavation progresses. In addition, as discussed in the previous <br />section, an east-west striking unnamed fault zone is mapped in the northwest <br />comer of the main pit. With the combination of faulting and discontinuities on the <br />north walls, the potential impact on the slope stability should be closely <br />monitored as mining continues. <br />6.2.3 West Walls <br />No major stability issues currently exist for the west walls of the main pit or <br />middle level of the quarry. Previous analysis indicated that the west highwalls <br />have approximately the optimum orientations for stability. Two west wall <br />orientations were analyzed in this study. The first had a dip direction of 091°, <br />and using this orientation the stereonet plot (Figure 15) indicated two plunges of <br />line intersections less than the angle of the slope face, and one intersecting set <br />of discontinuities that is within the failure envelope. Two of the intersections <br />were at angles lower than the critical friction angle and indicate that sliding along <br />-20- <br />