Tunnel Construction
Advancing tunnels cycle by cycle, under control, through variable ground.
The drill-and-blast cycle
Drill-and-blast tunnelling advances in rounds: drill the face to a designed pattern, charge and fire the round, ventilate and clear the muck, then support the ground before the next pull. Each round is a controlled repeat of the last, and the quality of the drilling and the firing sequence decides how clean the profile comes out. The full sequence is described in drill-and-blast tunnelling.
Control and profile
- Survey control of line and level, round after round
- Contour (smooth-wall) blasting for a clean, stable profile with minimal overbreak
- Cut design — the opening cut that gives the round a free face to break to
A well-designed round breaks to the planned outline with little overbreak, which means less scaling, less support and a stronger finished tunnel.
Ground support
Support is installed on a structured cycle, matched to the ground conditions, so the excavation stays safe as it advances. In variable ground the round length and support are adjusted rather than pushed.
Where it is used
Transport and utility tunnels, and access development in mining and hydraulic projects. The method shares its fundamentals with underground mining development — see also tunnel drivage by drill and blast.