2016-04-14_REPORT - M19741004 - Laserfiche WebLink

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Martin Marietta Materials Spec-Agg 2016 Annual Report to show signs of additional movement during the site visits for this study (Photo 5). As previously reported, the overall effective angle of the last three benches of the north pit walls has been modified to an angle of 35°, which is consistent with the 2003 Lachel geotechnical evaluation (Lachel, 2003). The failure surfaces (i.e., the surfaces along which movement has occurred) remain at a"residual strength" and therefore are less resistant to additional loading. Although the slope configuration is currently stable, the failure mechanism could potentially be reactivated, resulting in movement of additional material. The northern wall slopes should continue to be visually monitored for indications of instability. 6.0 ANALYSIS OF STRUCTURAL DISCONTINUITIES The stability of the rock mass that forms the quarry walls is primarily controlled by the presence of rock discontinuities, such as joints, foliation, and faults. Discontinuities can create surfaces for sliding, and the intersections of multiple discontinuities can define the boundaries of wedges or blocks that have the potential to slide. The orientations of discontinuity sets vary considerably throughout the quarry. Therefore, it is possible that discontinuity orientations in a specific location of the quarry could deviate from the discontinuity orientations assumed for the analyses presented in this report. 6.1 Evaluation of Discontinuity Measurements Representative discontinuity orientations for the quarry walls are required in order to evaluate the stability of the rock mass that forms the mine walls. Representative orientations for each discontinuity set observed were developed by analyzing the thousands of measurements collected since the beginning of the project. For the 2016 Annual Report, we evaluated how the data collected over the past year compares with the previous geologic structure dataset and the representative orientations of observed discontinuity sets previously selected for analysis. Using this approach, we are able to assess possible emerging trends related to the shift in orientation of the various observed discontinuity sets as more of the rock mass is exposed during mining operations. We analyzed the discontinuity orientation data using DIPS 6.017 (Rocscience, 2015). The program enables plotting of individual data points, and offers several methods of data analysis, including contouring or cluster analysis. We plotted the individual data points collected during the July and December 2015 site visits over contours for the entire dataset(from all previous years), and alongside representative discontinuity orientations used for the previous 2015 annual report(Figure 5). We also plotted this years' individual data points over contours for just this years' data (Figure 6). These figures show that the latest data is generally consistent with the representative orientations of discontinuity sets observed in previous years with a few emerging trends and exceptions. Joint set P-5 has emerged over more recent years and was again observed this year. A foliation set F3 was identified in previous years (prior to 2013), but has not been observed in the past three years and was absent from measurements this year. Joint set P-7 was identified in the 2013 report, but was not observed this year. A few data points for a new foliation identified in the 2015 report were observed again this year. These foliations may be localized and we will continue to monitor for the presence of this foliation trend during next year's study. Generally,joint sets P-1, P-2, and P-6 are the dominant joint sets observed this year(Figure 6). Arrows shown in Figure 6 indicate the shifts in representative orientations of the observed discontinuity sets based on our evaluation of the new data. February 8, 2016 Page 5 Lachel & Associates, Inc. Project 15364004.00 ©2016 All Rights Reserved