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WL D UFF RMR Aggregates, Inc. <br /> U N ❑ E R G R 0 U N C Rock Failure Analyses and Stabilization Report <br /> E NGIN E E R I N G,INC Mid Continent Limestone Quarry <br /> Rockfall Runout Setback <br /> A prescriptive setback was defined from the base of the highwall to the maximum extent of rock <br /> block endpoints across the three East face transects. The 2D sections illustrating the steps, bounce <br /> height and endpoints for the 3,000-block run are provided in Appendix E. The maximum endpoint <br /> block with the longest runout is highlighted. In all three transects, the maximum runout block was an <br /> outlier and considered a conservative estimate for probable rockfall. Figure 2b represents the setback <br /> zone from the base of the highwall that is defined by this conservative estimate for maximum rockfall <br /> runout. No man work shall be performed within the setback without additional stabilization or <br /> barriers. Figure 2b illustrates the rockfall maximum endpoints and the boundaries of the rockfall <br /> setback zone from the toe of the highwall. Coordinates of the setback and a Google Earth kmz file <br /> have been provided to RMRA to designate the setback. <br /> Rockfall Berm <br /> A rockfall berm was modeled on the three East face transects as a remedial measure to reduce the <br /> size of the setback zone (Figure 2b), defined above. The berm size and location were defined through <br /> an iterative modeling process to minimize the size of the berm and decrease the setback from the <br /> highwall toe. Based on computational rockfall modeling, we support using the equivalent of a berm <br /> composed of limestone scree with a height of 15 feet, crest width of 5 feet and maximum slope angle <br /> of 32 degrees. Maximum kinetic energies modeled along the ten transects are all within that <br /> tolerance of maximum allowable impact energy. Rockfall analyses provided in Appendix E indicates <br /> that 100% of simulated rockfall blocks were contained by the rockfall barrier, in tandem with the <br /> catchment basin. Where the rockfall berm is impacted by larger blocks, the barrier should be <br /> repaired. The berm is considered in tandem with a setback from the highwall toe that will act as a <br /> catchment basin. A Rockfall Catchment Area Ditch (RCAD) is recommended along the entire length of <br /> the East face. Parameters contributing to RCAD effectiveness include 1) slope height and angle, 2) <br /> ditch width, depth and shape, 3) anticipated block size and quantity of rockfall, and 4) effect on rock <br /> fall trajectories of slope irregularities (Wyllie and Mah, 2004). The RCAD will also act as a retention <br /> basin for fallen rock to be cleaned over time. Rockfall modeling of the RCAD and berm design is <br /> effective at reducing the southern extent of the rockfall setback zone. <br /> Long Term Inspection Program <br /> An effective proactive approach to slope stabilization will require a consistent, long-term program of <br /> inspections and periodic maintenance of the berm and catchment area. Rockfall blocks should not be <br /> permitted to accumulate. Damaged portions of the berm should be repaired immediately. Periodic <br /> inspections of the slope and outcrops by an engineering geologist or geotechnical engineer will be <br /> required over time to investigate natural deterioration of the stability conditions due to 1) <br /> weathering/erosion of the surface rock, 2) increases in fracture aperture by water causing loosening <br /> of surficial blocks, 3) loss of block interlock or support following minor block failure, and 4) growth of <br /> Page 9 <br /> 535 16th STREET,SUITE 620 1 DENVER,CO 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM <br />