2009-02-17_REPORT - M1974004 (2)

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1 5.2.1 East Wall ' Historically, the east wall has had no major instability issues. The stereonet plot for the east wall (Figure 11) was derived from the full dataset and shows multiple plunges of lines of intersection less than the angle of the slope face and one intersection that falls within the failure envelope. Consequently, the potential for sliding exists, but is unlikely, along many of these plane intersections, but sliding is only plausible along one. Foliation plane F-3 and joint P-5 are the only planes having a line of intersection that not only daylights the pit wall, but also plunges at an angle steeper than the angle of friction. Therefore, if this intersection of planes exists in the eastern wall area, sliding is kinematically feasible. All other plunge lines of intersecting planes that daylight the pit wall are inclined at an angle less than the angle of friction, and therefore are ' kinematically stable. For the temporary nearly vertical bench face (prior to reclamation), additional potentially unstable wedges may exist due to the steep overall slope angle (e.g. P3:P1 and P4:P1). These wedge failures have been observed occasionally on the east wall and are localized in extent. The development and size of these wedge failures will be controlled by the limited extent of the discontinuities mapped in the quarry, and by the limits on bench height. 5.2.2 North Walls Consistent with the previous LF&A annual reports, the north wall has been subdivided into two separate slopes for analysis: the northeast and the northwest walls. The instabilities observed in the eastern section of the wall and the differing slope 1 orientations necessitated the distinction between the two slopes. To take into account the shallower slope angle of the past three benches as well as the final mine plan design, a 35° overall dip angle for the slope was used in the analysis of each of the north walls. -15-