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Martin Marietta Materials <br />Spec -Agg 2013 Annual Report <br />2) The plunge of the lines of intersection exceeds the angle of friction. <br />On the stereonets, Markland's criteria for wedge sliding are satisfied when the intersection of two <br />discontinuities plot within the critical zone. <br />6.4.1.3 Toppling Failure <br />Toppling failures can occur where planes share a similar dip direction to the slope face and where they dip <br />relatively steeply into the slope face. In our opinion, toppling failure is not likely to be associated with large - <br />scale instability on the scale of an entire mine highwall. Therefore, toppling was not considered in our <br />kinematic analysis. However, small -scale toppling failures are likely to occur locally at the site contributing to <br />localized rockfall. <br />6.4.2 East Walls <br />For the 2013 annual report, we analyzed two east wall orientations based on the locations shown in Figure 2 <br />and Table 2: East Walls 1 and 2. East Wall 1 corresponds to the same wall location and orientation <br />analyzed in previous annual reports. East Wall 2 is a newly analyzed wall orientation for the 2013 annual <br />report. <br />The stereonet plot for East Wall 1 shows two discontinuity intersections that fall within the failure envelope <br />(i.e., critical zone), suggesting that wedge failure is kinematically possible for this slope orientation (Figure 9). <br />The intersecting sets that may result in wedge failure include foliation F -1 and joint P -3, and foliation F -1 with <br />joint P-4. Planar failure is not indicated as a potential failure mode in the stereonet plot for East Wall 1. <br />The stereonet plot for East Wall 2 shows one discontinuity intersection that falls within the failure envelope, <br />suggesting that wedge failure is kinematically possible for this slope orientation (Figure 9). The intersecting <br />set that may result in wedge failure includes foliation F -1 and joint P -4. Planar failure is not indicated in the <br />stereonet plot for East Wall 1. <br />Wedge failures were observed locally at station 13 -02 along the temporary eastern wall of the Main Pit <br />(Photo 4). The development and size of these wedge failures will be controlled by the variability and limited <br />lateral extent of the discontinuities. Based on the 2013 data set, foliation F -1 and joint P -4 have weak <br />signatures represented by relatively few measured orientations representing these features (Figure 6). As <br />excavation proceeds in the eastern walls, additional measurements are needed to refine the representative <br />discontinuity orientations of these joint and foliation sets in this area to evaluate their potential to contribute to <br />large -scale slope failure modes. <br />Our analysis indicates that potential planar and wedge failures may form in individual benches along the <br />eastern walls with near vertical faces during the temporary conditions prior to reclamation. <br />6.4.3 Northern Walls <br />For the 2013 annual report, we analyzed four northern wall orientations based on the locations shown in <br />Figure 2 and Table 2: Northeast Walls 1 through 3, and the Northwest Wall. Northeast Wall 1 and the <br />April 22, 2013 Page 13 Lachel & Associates, Inc. <br />Project 12361005.00 ©2013 All Rights Reserved <br />