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Martin Marietta Materials Spec -Agg 2015 Annual Report On the stereonets, Markland's criteria for wedge sliding are satisfied when the intersection of two discontinuities plot within the critical zone. 6.4.1.3 Topplinq Failure Toppling failures can occur where planes share a similar dip direction to the slope face and where they dip relatively steeply into the slope face. In our opinion, toppling failure is not likely to be associated with large -scale instability on the scale of'an entire mine highwall. Therefore, toppling was not considered in our kinematic analysis. However, small -scale toppling failures are likely to occur locally at the site contributing to localized rockfall. 6.4.2 East Walls For the 2015 annual report, we analyzed two east wall orientations based on the locations shown in Figure 2 and Table 2: East Walls 1 and 2 corresponds to the same wall location and orientation analyzed in the previous 2013 and 2014 annual reports. The stereonet plot for East Wall 1 does not indicate the possibility of planar or wedge failure. The stereonet plot for East Wall 2 shows one discontinuity intersection that falls within the failure envelope, suggesting that wedge failure is kinematically possible for this slope orientation (Figure 8). The intersecting set that may result in wedge failure includes joint P -5 and joint P -7. Planar failure is not indicated in the stereonet plot for East Wall 2. The development and size of these wedge failures will be controlled by the variability and limited lateral extent of the discontinuities. Based on the current and previous data set, joint P -5 and joint P -7 have weak signatures represented by relatively few measured orientations representing these features (Figure 6). As excavation proceeds in the eastern walls, additional measurements are needed to refine the representative discontinuity orientations of these joint and foliation sets in this area to evaluate their potential to contribute to large -scale slope failure modes. Our analysis indicates that potential planar and wedge failures may form in individual benches along the eastern walls with near vertical faces (30 feet in height) during the temporary conditions prior to reclamation. 6.4.3 Northern Walls For the 2015 annual report, we analyzed four northern wall orientations based on the locations shown in Figure 2 and Table 2: Northeast Walls 1 through 3, and the Northwest Wall correspond to the same wall locations and orientations analyzed in the previous 2013 and 2014 annual reports. 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 February 25, 2015 Page 12 Lachel & Associates, Inc. Project 14364006.00 02015 All Rights Reserved