2012-03-06_REPORT - M1974004 - Laserfiche WebLink

Home Browse Search

Martin Marietta Materials Spec -Agg Project the intersection of plane P -6 with the steeper dip for F -1 analyzed is just within the failure envelope, and so, if the foliation dips at 46° in this area, a potential for sliding does exist and should be monitored. The second western wall analyzed in this study, has a dip direction of 120° (Figure 14). The results for this analysis yielded fairly comparable results. There are three pairs of intersecting planes with plunge lines that daylight the slope face, but only two whose plunge lines are steeper than the angle of friction. The plunge of the intersection of discontinuities P1:P6 is just within the failure envelope as is the intersection of P2:F1. This combination of planes has not frequently been found to have potential for failure, but should be continued to be monitored and evaluated in future studies. 5.2.4 South Walls As with the north wall and west wall, the southern wall has also been subdivided into separate slopes for analysis: two southwest walls and a southeast wall orientation were selected based on the proposed Martin Marietta (formerly Lafarge) mine plan (Lafarge, 2003). This approach is the same as was used for previous annual reports, in which the southern walls were measured based on configurations on the proposed Martin Marietta mine plan. Figures 15 and 16 present the stereonets for each wall. In the southwest wall, the stereonet shows several pairs of intersecting planes that have plunge lines inclined shallower than the inclination of the slope face, but all are inclined less than the friction angle. Consequently, all pairs of planes are capable of forming wedge blocks, but none of these wedges are likely to be unstable. The stereonet also shows two pairs of intersecting planes that have plunge lines inclined steeper than the friction angle, but just steeper than the inclination of the slope face. As such both these wedges are considered kinematically stable. However, if isolated pairs of planes should intersect with shallower plunge angles due to natural variability, unstable blocks could daylight in the slope face and therefore these two pairs (P4:P6 and P5:P2) should continue to be monitored as the excavation continues. The wedge stability analysis for the southeast wall indicates five pairs of intersecting planes that have plunge lines inclined shallower than the slope face, with two of these (P3:P6) and (F3:P6) being inclined steeper than the friction angle and therefore, failure is possible along these planes. As mentioned previously for the east wall, the individual benches along the south walls with near vertical faces enable additional discontinuities to form potential wedges that may slide during the temporary conditions prior to reclamation. Wedge failures limited to individual benches have been consistently observed in the past along the south walls. In previous annual reports, toppling about discontinuity plane P -1 also existed as another mechanism of potential block movement for the southeast wall. However, as shown on Figure 16 both the slope face and discontinuity plane P -1 no longer share the same basic strike. A review of photographs during previous annual studies does indicate that there are continuous surfaces that form the face of the south wall. However, none of these surfaces appear to be identified as plane P -1, which has an average dip of 76° to the south. The foliation F -1 also strikes in the same general direction as both the southeast slope face and discontinuity plane P -1, although at an overall shallower dip. It is believed that the foliation will prevent large failure surfaces from developing along the south wall. This has been evident in the rock exposures on the south February 13, 2012 Page 12 Lachel & Associates, Inc. Project 11361017.00 ©2012 All Rights Reserved