Tunneling Ground Classification: Q_Barton
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 | Q max (dimensionless) | Q min (dimensionless) | TBM penetration rate m per hr (m/hr) | TBM utilization pct (%) | advance rate m per day (m/day) | class number | convergence pct (%) | cutter wear index | max unsupported span m (m) | notes | overbreak pct (%) | recommended support | rock class variant | shotcrete thickness mm (mm) | specific energy MJ per m3 | stand up time hr (hr) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Q_Barton | exceptionally_good__none | 1,000 | 400 | 2.8 | 55 | 48 | 2 | 0.05 | 0.05 | 30 | Q=400-1000: Exceptionally good rock. Essentially no support. Very high TBM performance expected. | 0.3 | none | exceptionally_good__none | 0 | 25 | 2,000 |
| Q_Barton | extremely_good__none | 400 | 40 | 2.6 | 52 | 42 | 3 | 0.1 | 0.1 | 20 | Q=40-400: Extremely good to exceptionally good rock. No support required except in special circumstances. | 0.8 | none | extremely_good__none | 0 | 28 | 720 |
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