2017-04-14_REPORT - M1974004 - Laserfiche WebLink

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Martin Marietta Materials Spec-Agg 2017 Annual Report For the 2004 analysis (Lachel, 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. This data was plotted on a chart showing dip angle in degrees versus elevation in feet (for chart see Lachel, 2004). The data resulted in an increase in the number of daylighting foliation planes that start at EL 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 50, average 28°) as determined from the 2003 Geotechnical Study(Lachel, 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 future 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 in the future. 6.4.4 West Walls For the 2017 Annual Report, we analyzed three west wall orientations based on the locations shown in Figure 2 and Table 2: West Walls 1 through 3. The wall locations and orientations correspond to the same wall locations and orientations analyzed in previous annual reports (Figure 2). The stereonet plot for West Wall 1 (Figure 11), adjacent to the Main Pit area, shows one discontinuity intersection that may fall within the failure envelope, suggesting that wedge failure is kinematically possible for this slope orientation. The intersecting sets that may result in wedge failure include joint P-1 and joint P-6. Planar failure is not indicated in the stereonet plot for West Wall 1 (Figure 11). The stereonet plot for West Wall 2, adjacent to the Southern Expansion Area, shows two discontinuity intersections that fall within the failure envelope, suggesting that wedge failure is kinematically possible for this slope orientation (Figure 12). The intersecting sets that may result in wedge failure include joint sets P-1 and P-6, and joint sets P-2 and P-7. Based on the 2015 data set,joint P-7 has weak signatures represented by relatively few measured orientations representing these features (Figure 6). Planar failure is not indicated in the stereonet plot for West Wall 2 (Figure 12). The stereonet plot for West Wall 3 shows one discontinuity intersection that may fall within the critical zone, suggesting that wedge failure is kinematically possible for this slope orientation (Figure 12). The intersecting sets that may result in wedge failure includes joint sets P-1 and P-6. The development and size of wedge failures will be controlled by the variability and limited lateral extent of the discontinuities. As excavation proceeds for West Wall 3, 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. Planar failure is not indicated in the stereonet plot for West Wall 3 (Figure 12). 6.4.5 Southern Walls For the 2017 Annual Report, we analyzed four southern wall orientations based on the locations shown in Figure 2 and Table 2: Southwest Walls 1 and 2, the South Wall, and the Southeast Wall. The wall February 27,2017 Page 10 Lachel &Associates, Inc. Project 16C64003 00 ©2017 All Rights Reserved