2012-03-06_REPORT - M1974004 - Laserfiche WebLink

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Martin Marietta Materials Spec -Agg Project 6.0 SUMMARY AND CONCLUSIONS The results of the structural geologic evaluation for the Spec -Agg Quarry, which includes field observations, historic performance, geologic mapping and stereographic analysis of structural geology data; indicate that the current quarry configuration appears to be stable under the existing conditions and current rock mass assumptions. The stability of each of the slopes is enhanced by the absence of significant hydrostatic pressures, by current mining procedures and by the current reclamation process being implemented by Martin Marietta at the site. F -3, the additional foliation set was initially identified in the 2005 study. To date, not enough data have been collected to fully develop a hypothesis regarding the location, extent and properties of the foliation; or to eliminate the possibility that F -3 is basically a signature of the undulating nature of the existing foliation set. The stereographic analysis indicates that the F -3 discontinuity plane may only have minor influence on the south walls and will not influence the north, west or east walls. 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. With respect to the quarry walls, the north walls are currently being mined at a slope angle of approximately 35° and are currently stable; and as stated in previous reports the slide that occurred on the northeast wall has shown no signs of continued movement since the steepness of the wall slope was modified in 1999. Based on data collected from boreholes in the 2003 geotechnical investigation, a number of relatively shallow foliation surfaces will be encountered below the current main pit elevation of 6,325 feet, starting at an estimated depth of 6,325 feet and the north walls should be monitored closely as the final 20 feet of excavation occurs. The remaining walls are also considered to be currently stable, though the present analysis for the west wall and both the southwest and southeast walls each indicate the possibility for wedge failures, and possibly planar failures, to occur. These two walls of the quarry should continue to be monitored closely as mining continues. 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. February 13, 2012 Project 11361017.00 Page 14 Lachel & Associates, Inc. ©2012 All Rights Reserved