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 Quarry 9. MINE STABILIZATION A summary of the mine operation plan recommendations, from a geotechnical perspective, is provided here to inform a full mine operation plan provided by RMRA under separate cover. The overall intent is to achieve long-term slope stability by eliminating the potential for headwall failure along the upper and lower limestone beds stratigraphically atop the massive limestone. The mine plan works under the assumption the upper and lower limestone beds planar slide failure mode atop the massive limestone, dipping to the south along the laterally continuous bedding plane, will only release in that direction. The mine plan is a phased and stepped approach working from the southwest corner of the headwall to the northeast with the intent to eliminate the possibility of permanent or temporary condition of the upper and lower limestone beds in the cutslope wall. It is the opinion of KUE that the upper and lower limestone beds should be removed completely from the highwall to minimize the risk of another release. This can be performed via multiple mining methods. RMRA will develop and discuss the process under their full mining plan. RMRA will perform this work from a safe position outside of the release plane. This approach stabilizes the slope for long term stability within the massive limestone. As stated above, there is a possibility of local wedges of the upper or lower limestone beds remaining where the bedding slope has locally dipped differently or a unknown joint in the top of the massive limestone has created a wedge. In these circumstances, if the wedge cannot be scaled or blasted safely, mechanical stabilization would be warranted for life safety. 9.1. ACTIVE MECHANICAL STABILIZATION Mechanical stabilization shall be utilized on the Mid Continent Limestone Quarry if the upper and/or lower limestone beds are encountered within a highwall or bench. Mechanical stabilization will be utilized to pin the upper and/or lower limestone beds to the massive limestone below with the use of tiebacks to increase the resisting force of the upper and/or lower limestone beds. A preliminary design of the anchorage system was performed. For this analysis, a 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 FOS 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. Potential upper and lower limestone slope heights ranging from 5 feet to 15 feet were modeled to determine the resisting force required to reach a FOS of 1.5 static and 1.3 seismic. Several mechanical stabilization methods were considered, ultimately a 7-strand anchorage was selected for both logistical purposes and the stand lengths can be changed to accommodate longer lengths for this difficult to reach location. In some modeled instances, the upper and lower limestone could exceed greater than 10 ft thickness which would require a long total length of 45 feet. Given the load and lengths necessary, a traditional bar would be exceptionally long requiring coupled bars and likely a crane, becoming logistically cumbersome. A concrete bollard with tie backs was also Page 15 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM