Tunneling Ground Classification: GSI
Rock mass classification systems for tunnel design — RMR (Bieniawski 1989), Q-system (Barton 1974), GSI (Hoek 2002), NATM classes, and squeezing potential (Hoek & Marinos 2000) with support requirements, TBM performance parameters, and convergence estimates
| classification system | rock class | GSI max (dimensionless) | GSI min (dimensionless) | bolt length m (m) | bolt spacing m (m) | class number | max unsupported span m (m) | notes | recommended support | rock class variant | shotcrete thickness mm (mm) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| GSI | III_very_blocky__systematic_bolts | 50 | 35 | 4 | 1.5 | 3 | 10 | GSI 35-50: Very blocky interlocked partially disturbed blocks with many weathered joints. Systematic bolts and shotcrete required. | systematic_bolts | III_very_blocky__systematic_bolts | 100 |
| GSI | II_blocky__spot_bolts | 75 | 50 | 3 | 2.5 | 2 | 15 | GSI 50-75: Blocky rock with well interlocked undisturbed blocks. Rough slightly weathered joints. Moderate support. | spot_bolts | II_blocky__spot_bolts | 50 |
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