2020-11-05_REVISION - M1973021 (12)

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Table 5-2. Summary of Recommended Hoek-Brown Material Inputs for Sillimanitic Gneiss Parameter Description Selected Basis Value UCS 0 Uniaxial compressive strength of Avg. value of 3 UCS tests ( ) 65 ksi intact specimen from lab testing . performed in 2018 Geologic Quantified value of rock mass Based on blocky, disturbed Strength Index based on visual assessment of 35 rock mass with Fair to Poor (GSI) structure and the condition of discontinuity surfaces discontinuities Material Recommended lower bound Based on rock type 23 value from Roc Lab for Constant (m) gneiss bedrock (28 ± 5) Disturbance Accounts for disturbance due to 0 (Global) Failure planes likely deep Factor(D) blasting 1 (Local) and not disturbed by blasting. Modulus Ratio Recommended value from (MR) Based on rock type 500 RocLab for gneiss bedrock (500 ± 225) 5.2 Rock Mass Rating Rock Mass Rating (RMR) system was developed by Bieniawski (1976)to classify structural features of exposed rock. The RMR method quantifies a rock mass by assigning a number to exposed rock in the categories of intact rock strength, the estimated RQD, discontinuity spacing, favorable or unfavorable discontinuity orientation, the discontinuity persistence, discontinuity aperture, feature roughness, strength, weathering, and presence of groundwater. The values assigned to each category are summed to produce a final RMR value, which ranges from 0 to 100. The final RMR value is then used to qualify the rock mass strength as very good, good, fair, poor, and very poor. RMR values have been collected at the South Quarry each year between 2013 and 2019 as part of the annual inspection and reporting. The inspections included measuring rock features including joint and foliation orientation, discontinuity spacing, discontinuity persistence, roughness, and other factors at exposed highwall locations in the active South Quarry (GEI, 2013 and GEI, 2019). The measurements are collected using visual methods and scanline surveys performed approximately 100 ft from the base of the excavated slopes. RMR values for the active South Quarry based on the highwall conditions observed during annual inspection mapping and are included in Appendix C.2. RMR values are not available for the West Quarry due to the lack of excavations in this location. The RMR values for the active South Quarry are summarized in the histogram in Figure 5-2. The two peaks in the histogram represent the typical maximum and minimum RMR values based on the highwall observations and suggest that average low and high values of RMR equal to 30 and RMR equal to 55 are reasonable for the active South Quarry highwall. The reason for the two peak RMR values is based on the method used during the annual 20 Aggregate Industries—Morrison Quarry GEI Consultants, Inc. AM-07 Geotechnical Stability Exhibit November 2020