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3.5 Rock Mass Rating <br />Bieniawski's RMR system combined five rock mass characteristics of both intact <br />• <br />• <br />properties and conditions of discontinuities. <br />1. Strength of intact rock <br />2. Rock quality designation <br />3. Spacing of discontinuities <br />4. Condition of discontinuities <br />5. Groundwater conditions <br />Table 4 presents the geomechanics classification and rock mass conditions determined by <br />adding ratings for these five parameters. The rating for the Upper Marine Sandstone and <br />immediate roof exceed 60, falling into the good rock category. <br />Table 4-Bieniawaski's rock mass rating. <br />Rating 81-100 61-80 41-60 21-40 <20 <br />Class number 1 2 3 4 5 <br />Description <br />I <br />Very good rock <br />Good rock <br />Fair rock <br />Poor rock <br />Very poor <br />rock <br />Maleki Technologies, Inc. <br />Page 15