Laserfiche WebLink
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 />addition, as discussed in the previous section, an east-west striking unnamed <br />fault zone is mapped in the northwest corner of the main pit. With the <br />combination of faulting and discontinuities on the north walls, the potential impact <br />on the slope stability should be closely 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 13) 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 />these surfaces is possible but unlikely. For the set that is within the failure <br />envelope (i.e. P-1 and P-6) sliding is assumed to occur because the plunge of <br />the line of intersection slightly exceeds the 33° angle of friction. <br />The second western wall analyzed in this study, has a dip direction of 120° <br />(Figure 13). The results for this analysis yielded fairly comparable results, with <br />two intersecting planes falling outside the failure envelope and one set mapped <br />within. The intersection of discontinuities F-1 and P-2 fall just within the shaded <br />region and sliding is assumed to occur as the plunge of the line of intersection <br />exceeds the 33° angle of friction. <br />zt - <br />