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Short note: Tunnel excavation by blasting

Short answer

Blasting excavation follows a cycle of drilling holes in a pattern, charging with explosives, blasting with delay detonators, ventilating, scaling, mucking and supporting. Hole types are cut, easers, contour and lifters. It is flexible and cheap but slower than TBM, with overbreak, vibration, fumes and strict safety needs.

Write a short note on tunnel excavation by blasting.

Tunnel excavation by blasting (drill and blast) is the traditional method for hard rock tunnels, widely used in Nepal's hydropower and road tunnels.

Cycle

  1. Drilling: holes (32-45 mm diameter, 3-4 m deep) are drilled with a drill jumbo according to the blast pattern.
  2. Charging: explosives (dynamite, emulsion or ANFO) and detonators are placed, and the holes are stemmed.
  3. Blasting: firing in sequence using delay detonators.
  4. Ventilation: clearing of fumes and dust.
  5. Scaling and mucking: loose rock is removed, and the muck is carried away.
  6. Support: rock bolts, shotcrete, or steel ribs.
   Face drilling pattern (cut holes in middle)
        o   o   o   o
      o   o  [x x]  o   o      x = cut / empty holes
        o   o   o   o
      Cut - stopers - contour (perimeter) holes

Hole types

Cut holes (open the face first), easers/stopers (enlarge), contour holes (smooth blasting for a clean profile), and lifters (floor).

Merits and limits

It is flexible for any section and rock, uses cheap equipment, and has a low initial cost. But it is slower than a TBM, causes overbreak, vibration, fumes and noise, and needs strict safety control, licensed blasters and explosive storage.

✓ Answer checked by Claude Opus 5.5 (high effort)

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