2024-03-29_REVISION - M1982121 (2)

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KILDUFF RMR Aggregates, Inc. u N D E R G R D U N C Rock Failure Analyses and Stabilization Report E N G I N E E R I N G.I N C Mid Continent Limestone Quarry and kinematic conditions for sliding. This point must fall outside the cut slope's great circle but within the rock friction kinematic boundary cone to be considered to have the potential for wedge sliding (red-shaded area in Appendix C figures). The thin interbed of shaley mudstone observed along some of the limestone bedding planes creates a potential failure plane of lesser cohesion and fiction angle than the limestone. Stability modeling was completed to evaluate this geometry for potential failure. 4. STABILITY MODELING ANALYSES OF FAILURE MODES Long Term Steady-State stability analyses along the cut slopes were performed to evaluate the potential bedrock failures along discontinuities in the rock mass. Results from these analyses were used to evaluate the cause of failure on the West wall and informed the conceptual design and mitigation support for the East and West faces. General limit equilibrium method slope stability analyses for the East and West face were performed using the software program RocPlane from RocScience (v.4.011). A factor of safety is calculated by modeling the effects of joint shear strength (in this case, primarily the weak interbed), water pressure within the joint,joint orientation and slope geometry intersections within a Monte Carlo sampling method.The models were checked by the limit equilibrium method of slices (Morgenstern-Price) using the software program Slope/W from Geostudio 2023.1. Using this methodology, the factor of safety for a given geometry is determined by calculating the ratio of resisting forces to driving forces on trial failure surfaces. Slip surface scenarios analyzed for this report were block specified.The slip surface with the lowest factor of safety against sliding is described as the minimum factor of safety for the defined conditions. The Long Term Steady-State was analyzed to consider the extended term stability of the highwall, and the rock strength is characterized by effective stress parameters. To determine the geologic input parameters for the Mid-Continent Limestone Quarry stability modeling, characteristic values of the Leadville limestone were initially taken from empirical data in peer-reviewed publications and verified by publicly available typical values for the units encountered on the slope. Based on tests performed by the United States Bureau of Reclamation' on the Leadville Limestone in the Paradox Valley, the friction angle of the limestone is approximately 40 degrees, and the cohesion is approximately 3,050 psi. CaltranS6 estimates for hard rock masses, like limestone, the friction angle of the rock mass varies from 35 degrees to 45 degrees and the friction angle of the joint areas can vary from 35 degrees to 40 degrees. No site-specific strength testing has been completed. Mohr-Coulomb strength criterion framework was utilized to define bedrock and joint material strengths. Mohr-Coulomb assumes an inherent cohesion in over-consolidated fine-grained or cemented soils and bedrock. And finally, a back analysis of the West face ground event was used to corroborate these empirical values. The West face stability analyses parameters were manipulated to achieve a Factor of Safety (FOS) of less than 1.0, in both RocPlane (FOS 0.99) and checked in Slope/W (FOS 0.92), indicating probable failure (Appendix D). Initially the back analysis in RocPlane considered 5 Ake, J., Mahrer, K., O'Connell, D., Block, L., 2005, Deep Injection and Closely Monitored Induced Seismicity at Paradox Valley, Colorado., United States Bureau of Reclamation. 6 California Department of Transportation., 2013, Rock Strength and Its Measurements. Page 6 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM