- 2071 Bhadra · 6 marks
Methods of tunnel excavation
Short answer
Tunnel excavation methods include drilling and blasting for hard rock, mechanical excavation by TBM or roadheader, heading and bench for large sections, soft-ground methods like shield, pipe jacking, cut-and-cover and NATM, plus multiple drifts and ripping. The choice depends on geology, tunnel size and length, water inflow, equipment, schedule and cost.
Discuss the methods of tunnel excavation.
Tunnel excavation methods depend on the type of ground, the size and length of the tunnel, time, and cost.
1. Drilling and blasting (drill and blast)
Holes are drilled in the face, charged with explosives and blasted; the muck is removed and the roof is supported. Used in hard rock; flexible for any shape. Steps: drilling, charging, blasting, ventilation, mucking, scaling and support.
2. Mechanical excavation
- TBM (full face): a rotating cutter head cuts the whole section and the muck is carried away by conveyor. Fast and safe for long tunnels.
- Roadheader: a boom-mounted cutting head for soft to medium rock and for tunnels of variable shape.
3. Heading and bench method
The tunnel is excavated in two stages: a top heading first (which is supported), then the bench below. Used in large sections.
4. Soft-ground methods
Shield tunnelling, pipe-jacking or micro-tunnelling, cut-and-cover (open trench, then roof), and the New Austrian Tunnelling Method (NATM) with shotcrete and rock bolts.
5. Other methods
Multiple drifts (side drift, centre drift), and excavation by ripping or hydraulic breakers.
Choice factors: geology and rock quality, tunnel length and diameter, water inflow, available equipment, and the schedule and cost. Support (rock bolts, shotcrete, steel ribs) follows each method to keep the opening stable, and the lining is built afterward.
✓ Answer checked by Claude Opus 5.5 (high effort)
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