2015-03-11_REPORT - M1974004 - Laserfiche WebLink

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Martin Marietta Materials Spec -Agg 2015 Annual Report 7.0 CONCLUSIONS AND RECOMMENDATIONS The results of the structural geologic evaluations and kinematic structural discontinuity analyses for the Spec -Agg Quarry do not indicate any immediate concerns with respect to large -scale instabilities in the current final quarry wall faces based on our field observations and current rock mass assumptions. The stability of the slopes is enhanced by the absence of significant hydrostatic pressure, by current mining procedures, and by the current reclamation process being implemented by Martin Marietta at the site. While large -scale failures are not anticipated, the slope will continue to shed rocks (minor raveling) over time as a result of small -scale failures (planar or wedge failure), particularly in near - vertical temporary bench faces. For the 2015 annual report, kinematic analyses are based on discontinuity measurements derived principally from data collected from the existing growing dataset supplemented with data collected during the June and December 2014 site visits. The results of these analyses are not intended to supersede results of analyses performed for prior years that were based on representative discontinuity orientations generated from the entire set of measurements. Rather the analyses presented herein are meant to compliment previous years' analyses and enable monitoring of possible new trends in the data that could result in previously unconsidered failure modes. The collected data for this evaluation was complimentary to and were consistent with past analyses. It is noted that the results for the current analysis did not change the pole or the resultant concentration center for any of the delineated joint sets significantly from any of the recent years' results. In general, the data collected during the June and December 2014 site visits correspond reasonably well with representative discontinuity orientations used in previous reports; however, we noted some minor differences which we applied to our kinematic analyses for the 2015 annual report. The kinematic analysis for East Wall 1, Northeast Walls 2 and 3, Northwest Wall, West Walls 1, 2 and 3, and Southeast Wall each indicate the possibility for wedge failures to occur. Additionally, the analysis for Northeast Walls 1 and 3 shows the potential for planar failure. The walls of the quarry in these areas should continue to be monitored closely as mining continues to assess the potential for the indicated failure modes to contribute to large -scale slope instability of a final mine highwall based on the continuity, regularity and variation in orientations of the discontinuities involved. We also recommend that known faults are tracked and observed in new exposures to confirm orientation and character for supplemental stability analysis, as needed. We expect the southern fault identified by Gable (1968) and in previous years site visits (Figure 3) may be exposed in other locations as excavations continue in the Southern Expansion Area. Additionally, the unmapped fault generally located in the central portion of the quarry may be exposed for mapping in the future. In addition, as recommended in the previous reports, evaluations will be conducted during future investigations to assess whether or not any of the foliation sets (F -1 through F -3) are caused due to localized faulting that may have resulted in "structural regions" that have created areas in which the varying orientation of the foliation planes occur. These questions will continue to be addressed as more data are collected. As documented in the past, localized raveling, especially along the south walls is likely to continue. Continuation of the safety- minded policies already in place, which limit the height of the exposed highwall as well as the reclamation of exposed highwalls as soon as possible following blasting and rock haulage, will aid in minimizing the potential for instabilities to occur. The quarry walls appears to be relatively dry February 25, 2015 Page 16 Lachel & Associates, Inc. Project 14364006 00 02015 All Rights Reserved