- 2074 Bhadra · 1 mark
Meaning of rock class and shear parameter
Short answer
Each RMR rock mass class is assigned cohesion and friction angle values, decreasing from over 400 kPa and 45° for very good rock to below 100 kPa and 15° for very poor rock. These parameters are used in the Mohr-Coulomb failure criterion for stability design.
Describe the meaning of rock mass class with respect to shear parameters.
In the RMR system each rock mass class is given shear strength parameters of the rock mass, cohesion and angle of internal friction . They decrease as the class goes from very good (I) to very poor (V):
| Class | Rock mass | Cohesion (kPa) | Friction angle |
|---|---|---|---|
| I | Very good | above 400 | above 45° |
| II | Good | 300 to 400 | 35° to 45° |
| III | Fair | 200 to 300 | 25° to 35° |
| IV | Poor | 100 to 200 | 15° to 25° |
| V | Very poor | below 100 | below 15° |
These values are used in the Mohr-Coulomb relation for stability and support design.
✓ Answer checked by Claude Opus 5.5 (high effort)
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