Rock Mass Classification: GSI
Rock mass classification systems — RMR (Rock Mass Rating), Q-system (Barton), and GSI (Geological Strength Index) — with rating ranges, rock quality descriptions, support recommendations, and estimated strength/deformation parameters
| classification system | parameter or class | cohesion kPa max (kPa) | cohesion kPa min (kPa) | estimated modulus gpa max (GPa) | estimated modulus gpa min (GPa) | friction angle deg max (deg) | friction angle deg min (deg) | notes | rating max (dimensionless) | rating min (dimensionless) | rock mass description | support recommendation |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GSI | Blocky_Disturbed_Poor | 25 | 0 | 2 | 0.1 | 30 | 20 | GSI 20-35; poor; heavily disturbed; Em 0.1-2 GPa; D=1.0 for heavily blasted or mechanical excavation | 35 | 20 | Blocky/disturbed - folded with angular blocks | Medium steel ribs + shotcrete; forepoling |
| GSI | Blocky_Good | 100 | 50 | 20 | 5 | 45 | 35 | GSI 55-75; undisturbed blocky mass; Em 5-20 GPa for typical tunnel rock; D=0 for tunnels per Hoek 2002 | 75 | 55 | Blocky - well interlocked undisturbed rock mass | Systematic bolting; local shotcrete |
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