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increasing the bench width and decreasing the bench height to a minimum 40H:40V for <br /> sillimanitic gneiss. <br /> 8.1.2 Recommendations for Kinematic Stability <br /> The kinematic evaluation and review of historical rockfalls indicates that the orientation and <br /> condition of discontinuities has a strong influence on localized block failures. The dominant <br /> discontinuity pattern of horizontal foliations and near-vertical joints suggest that the average <br /> configurations are generally favorable for kinematic stability, but deviations from the <br /> dominant patterns could result in unstable rock blocks. Photo 7-3 highlights areas where <br /> steep, adversely oriented foliations resulted in localized failures when the toe of the slope is <br /> undermined. These failures likely occur during mining operations and present a risk to <br /> operators during the excavation process, and kinematic failures will likely become more <br /> frequent in these areas if the bench configuration is steepened. The failures observed in <br /> Photo 7-2 suggest that the adversely oriented foliations have a persistence that can extend <br /> between multiple benches. If the highwalls in this area are steepened further it could result in <br /> a failure that encompasses several benches and a large rock mass. This concern is <br /> highlighted in Photo 8-1 which shows the kinematic failures from a plan view and indicates <br /> that the upper extent of the failures extends nearly to the toe of the overlying bench. <br /> GEI recommends that Aggregate Industries address the potential for kinematic failures with a <br /> detailed assessment and evaluation of discontinuity conditions. Adversely oriented <br /> discontinuities are typically observed following blasting operations, as material is being <br /> hauled from the highwall bench. If foliations or fractures are steeply dipping into the <br /> excavation and the strike is parallel to the bench face, the overlying rock block needs to be <br /> considered unstable and a setback equal to two times the bench height should be established <br /> for operator safety. Additional excavation should not occur until a site-specific geotechnical <br /> assessment and evaluation can be performed. The assessment must consider the orientation <br /> of the observed discontinuities and planned geometry of underlying bench, and a kinematic <br /> evaluation should be performed using discontinuity and geometric information specific to the <br /> observed bench conditions. The site-specific information should be evaluated using <br /> kinematic evaluation software such as the RocScience Swedge, RocPlan, RocTopple, and <br /> RocFall. These programs are used to produce an estimated factor of safety and to <br /> characterize the potential impacts should failure occur. If results show the potential block <br /> does not meet safety requirements the horizontal bench horizontal bench width should be <br /> increased. <br /> 41 <br /> Aggregate Industries—Morrison Quarry GEI Consultants, Inc <br /> AM-07 Geotechnical Stability Exhibit November 2020 <br />