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Morrison Quarry AM-07 Geotechnical Stability Exhibit <br /> DRMS Permit M-1973-021 <br /> Aggregate Industries WCR Inc. <br /> Strength Estimates for Localized Bench Failures <br /> The localized bench stability evaluation includes highwalls as steep as 30H:70V and slopes as high as 250 <br /> feet. Strength evaluations under this situation accounts for disturbance due to blasting at the highwall <br /> face or rebound from stress relief. <br /> The Hoek-Brown method uses values from laboratory testing as well as geologic strength index(GSI) <br /> values to develop non-linear strength criterion for a rock mass. The criterion is given by the following <br /> formula: <br /> Q ll <br /> U1 = U3 + Uci (Mb 3+ S aI <br /> Uci <br /> where mb, s, and a are the rock mass material constants given by <br /> mb = mi exp[GSI-100] <br /> 28-14D <br /> S=exp[(GSI-100)/(9-3D)] <br /> a=1/2 + 1/6 (e-GSI/15_e-20/3) <br /> Key input parameters for the generalized Hoek-Brown criteria are the intact uniaxial compressive <br /> strength (6c;), the GSI, material constant (m;),the disturbance factor(D), and either the intact modulus <br /> (Ei) or the rockmass modulus ratio (MR). The input parameters for localized bench failures and selected <br /> values are summarized below. <br /> Parameter De pn, Selected Basis <br /> UCS (oci) Uniaxial compressive 12.5 ksi Avg. value of 7 UCS tests <br /> strength of intact specimen performed in 2018 <br /> from lab testing <br /> Geologic Strength Quantified value of rock mass 40 Based on blocky, disturbed <br /> Index (GSI) based on visual assessment rockmass with Fair to Good <br /> of structure and the discontinuity surfaces <br /> condition of discontinuities <br /> Material Constant Based on rock type 28 Recommended value from Roc Lab <br /> (m;) for gneiss bedrock(28±5) <br /> Disturbance Accounts for disturbance due 1 Production blasting used for <br /> Factor(D) to blasting highwall excavations <br /> Modulus Ratio Based on rock type 500 Recommended value from RocLab <br /> (MR) for gneiss bedrock(500±225) <br /> The associated criterion is below: <br /> Hoek Brown Criterion-Local Bench Failures <br /> b 0.385386 <br /> s 0.0000454 <br /> a 0.511368 <br /> GEI Consultants, Inc. 3 of 25 Appendix CA <br /> November 2020 <br />