Table 11 Guidelines for excavation and support of 10 m span rock tunnels in accordance with the RMR System (After Bieiniawski 1989)
Rock mass class | Excavation | Rock bolts (20 mm diameter, fully grouted) | Shotcrete | Steel sets |
|---|---|---|---|---|
I—Very good rock RMR: 81 –100 | Fullface, 3 m advance | Generally no support required except spot bolting | ||
II—Goodrock RMR:61–80 | Fullface, 1–1.5 m advance. Complete Support 20 m fromface | Locally, bolts in crown 3 m long, spaced 2.5 m with occasional wire mesh | 50 mm in crown Where required | None |
III—Fair rock RMR:41–60 | Top heading and bench 1.5 –3 m advance in top heading Commerce support after each blast Complete support 10 m from face | Systematic bolts 4 m long Spaced 1.5–2 m in crown And walls with wire mesh In crown | 50–100 mm in crown and 30 mm in sides | None |
IV—Poor rock RMR: 21 –40 | Top heading and bench 1.0 –1.5 m advance in top heading Install support concurrently with excavation, 10 m from face | Systematic bolts 4–5 m long, spaced 1–1.5 m in Crown and walls with wire mesh | 100–150 mm in Crown and100mm insides | Light to medium ribs Spaced 1.5 m where required |
V—Very poor rock RMR: < 20 | Multiple drifts 0.5–1.5 m advance in top heading Install support concurrently with excavation. Shotcrete as soon as Possible after blasting | Systematic bolts5–6 m Long spaced 1–1.5 m in Crown and walls with wire mesh. Bolt invert | 150–200 mm in crown,150 mm in sides,and50mm On face | Medium to heavy ribs spaced 0.75 m with steel Lagging and forepoling if required. Closed invert |