2023-08-31_ENFORCEMENT - M1982121

Home

K1L D UFF RMR Aggregates, Inc. J N ❑ E R G R O U N ❑ Rock Failure Analyses and Stabilization Report NGIN E E R I N G,INC. Mid Continent Limestone Quarry vegetation roots. Inspections after seasons of significant precipitation should be a high priority, particularly with freeze-thaw potential. 6. LONG-TERM STABILIZATION AND CONFIGURATION Long-term steady state stability analysis of the west face highwall within the massive limestone was performed to evaluate the potential bedrock failures along simulated discontinuities in the rock mass. No weak interbeds or adverse bedding planes daylight in the massive limestone in the active quarry wall. The January 2023 ground event failed along the lower weak bed above the massive limestone. The massive limestone was modeled at various slopes angles to determine the stability of the lower limestone layer.The slope geometry was analyzed using limit equilibrium method slope stability analyses using the software program Slope/W from Geostudio. Geologic input parameters defined above were used for stability modeling. 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. A factor of safety is calculated by modeling the effects of joint shear strength, friction angle, and water pressure within tension cracks. Based on information provided by RMRA mining staff and WE site reconnaissance, no known tension cracks or discontinuities are visible or known to exist within the massive limestone layer. For the analysis, tension cracks were placed within the upper slope of the highwall to simulate long-term weathering and the release plane comparable to the ground event of the west slope. The tension cracks were modeled as 50%water-filled plane. Strength properties of the massive limestone utilized empirical values similar to those used within the west slope back analysis to provide a conservative factor of safety due to no site-specific strength testing having been completed. The Colorado Department of Reclamation Mining and Safety (DRMS) recognizes that a suitable minimum factor of safety is dependent on the engineering analyses performed, accuracy of model input parameters and level of impact to life and facility safety. The FOS values recommended by the Colorado DRMS7 are scaled based on the robustness of input parameters and analyses weighted by the consequence of failure. The Colorado DRMS recommended FOS values are reproduced in Table 4 below. 'Colorado Division of Reclamation, Mining and Safety,2016, Design Standard of Care for Slope Stability/Geotechnical Analyses. Page 10 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM