2024-02-02_REVISION - M1982121 (6)

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KILDUFF RMR Aggregates, Inc. U N D E R G R a U N D Rock Failure Analyses and Stabilization Report E N G I N E E R I N G.I N C Mid Continent Limestone Ouarry Results from that static model run reduce the FOS significantly to FOS 1.40 for a 1:1 geometry and to FOS 1.54 for a 1.4:1 geometry. Given that consideration of an unknown zone of weakness within the massive limestone, albeit not previously documented, KUE recommends a H:V bench slope geometry of 1.4:1 or larger is deemed acceptable, using the accepted static minimum FOS of 1.5 and seismic minimum FOS of 1.3 7. BLASTING IMPACTS TO STABILITY The Mid-Continent Quarry site is approved for blasting per the permit. Therefore, the impact that blasting may have on the slope stability above the mine during active-mining and post-mining periods were evaluated. No direct measurements of peak particle velocity(PPV) have been measured on site during blasting, only at a distance from the mine near the closest general population structures, where the PPV was measured at 0.0 inches/second. The assumption is made, based on conversations with RMRA staff, that RMRA staff use conservative, proper blast design with delay timing in order to keep PPV values low. As outlined in Appendix G, a conservative PPV of 0.3 inches/second was selected from the US Department of Interior10 report on ground vibration from surface mine blasting identifying PPV values over a scaled distance for blasting in quarries. A frequency (f) of 25 Hz was selected from the same empirical reference as the peak of the occurrence histogram for quarry blasting. Given these parameters, Wyllie and Mah provide a means to calculate horizontal acceleration due to blast vibration, as shown in Appendix G: 2 * Tc *f * PPV a = 9 From this KUE calculate a kh of 0.12, which is less than the design seismic coefficient base on the peak ground acceleration for a 1,000-year return period of 0.196 (Appendix G).Therefore, the pseudostatic seismic acceleration parameter is more conservative and controls the analyses. Ultimately the ground vibration levels are a result of the release of explosive energy, which may also potentially cause excessive flyrock or backbreak.To avoid high vibration levels, RMRA should continue to consider energy distribution, powder factor and particularly energy confinement for the selected bench geometry. 8. JULY 6 SITE RECONNAISSANCE A site reconnaissance on the West wall was performed on July 6, 2023 with RMRA staff and Ben Langenfeld of Lewicki & Associates to evaluate the north limit of the upper limestone beds and formulate a plan across represented disciplines to determine the optimal quarry headwall extent for long-term slope stability using the modeled long-term slope geometries discussed above. Photos with detailed captions from the reconnaissance are included in Appendix F. io U.S. Department of the Interior,Office of Surface Mining, 1980,Structure Repsonse and Damage Produced by Ground Vibration from Surface Mine Blasting; Report of Investigations 8507. Page 13 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM