2014-05-02_REPORT - M1974004 - Laserfiche WebLink

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Martin Marietta Materials Spec -Agg 2014 Annual Report The stereonet plot for Northeast Wall 1 indicates a potential planar failure mode along foliation F -1 for this slope orientation (Figure 9). This is the same foliation orientation that was believed to contribute to the 1998 slope instability in the Northwest Wall. The stereonet plot for Northeast Wall 1 does not indicate the possibility of wedge failure (Figure 9). The stereonet plot for Northeast Wall 2 shows one discontinuity intersection that fall within the failure envelope, suggesting that wedge failure is kinematically possible for this slope orientation (Figure 9). The intersecting sets that may result in wedge failure include foliation F -1 and joint P -3. Planar failure is not indicated in the stereonet plot for Northeast Wall 2. As described above, the development and size of wedge failures will be controlled by the variability and limited lateral extent of the discontinuities. As excavation proceeds in the Northeastern walls, additional measurements are needed to refine the representative discontinuity orientations of these joint and foliation sets in this area to evaluate their potential contribute to large -scale slope failure modes. The stereonet plot for Northeast Wall 3 indicates a potential planar failure mode along foliation F -1 for this slope orientation (Figure 9). This is the same foliation orientation that was believed to contribute to the 1998 slope instability in the Northwest Wall. The stereonet plot for Northeast Wall 3 shows two discontinuity intersections that fall within the failure envelope, suggesting that wedge failure is kinematically possible for this slope orientation (Figure 9). The intersecting sets that may result in wedge failure include foliation F -1 and joint P -3, and joint sets P -2 and P -7. Based on the 2014 data set, joint P- 7 has weak signatures represented by relatively few measured orientations representing these features (Figure 6). The Northeast Wall 3 was not accessible for direct measurements or observations during this annual study. Additional measurements and observations are needed to assess the potential for large scale planar sliding along foliation F -1 as excavation continues to extend below the Northeast Wall 3. The stereonet plot for Northwest Wall shows one discontinuity intersection that falls within the failure envelope, suggesting that wedge failure is kinematically possible for this slope orientation (Figure 10). The intersecting sets that may result in wedge failure include foliation F -1 and joint P -2. Planar failure is not indicated in the stereonet plot for Northwest Wall (Figure 10). For the 2004 analysis (L&A, 2004), the long -term impact of foliation F -1 on the stability of both the northeast and northwest walls was further investigated using discontinuity data that included elevation information for the foliation orientation. These data were plotted on a chart showing dip angle in degrees versus elevation in feet (for chart see L &A, 2004). The data resulted in an increase in the number of day lighting foliation planes that start at an elevation of 6,325 ft and continue with increased frequency to below the planned final pit elevation. Due to the possibility of a lower friction angle along the foliation plane (as low as 5 °, average 28 °) as determined from the 2003 Geotechnical Study (L&A, 2003), the potential exists for future instabilities to occur on the northern walls as the pit is excavated to its final depth. These shallow dipping discontinuities along the foliation can have a significant impact on the stability of the north wall and should be monitored closely as excavation progresses. As discussed in the previous section, an east -west striking unnamed fault zone was previously exposed in the northwest corner of the main pit. In addition, a north -south trending fault has been newly mapped based on our observations from the recent site visits. Due the presence of faults and potentially adverse discontinuity orientations on the north walls, the slopes should be closely monitored as mining continues. March 31, 2014 Page 13 Lachel & Associates, Inc. Project 13364013 00 02014 All Rights Reserved