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 Results from that static model run with reduced cohesion decrease 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 calculates a kh of 0.12, which is less than the design seismic coefficient based 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. Currently, there is no seismic design code for rock slope stability. Due to the similarities between soil nail design and rock dowel design, the seismic design methodology from FHWA GEC 7 was utilized which was developed following AASHTO LRFD Bridge Design Specifications. The peak ground acceleration (PGA) and horizontal response spectral acceleration were determined from AASHTO 1,000-year return period maps. Site adjustment factors are then determined based on the site class, PGA, and horizontal spectral acceleration values to calculate the site corrected PGA and response acceleration. With these values, the design seismic coefficient is calculated. 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. io U.S. Department of the Interior,Office of Surface Mining, 1980,Structure Response 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