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Conventional tunnelling steps and TBM advantage

Short answer

Conventional drill and blast sequence is survey, drill blast holes, charge, blast, ventilate, scale, muck, install temporary support, repeat the cycle, then place final lining. A TBM is a rotating cutter head machine that excavates the full section continuously. Advantages are high speed, smooth wall with less overbreak, safety, less labour, and suitability for long tunnels.

Explain the steps to be followed in sequence while carrying out tunneling work by using conventional method. Introduce TBM and its advantage in tunnel construction.

Conventional (drill and blast) method: steps in sequence

  1. Survey and marking of the face profile, centre line and level.
  2. Drilling blast holes in the planned pattern using a drill jumbo.
  3. Charging the holes with explosives and detonators, and connecting.
  4. Blasting after everyone leaves, using the proper delay sequence.
  5. Ventilation to clear fumes and dust.
  6. Scaling: removing loose rock from the roof and sides.
  7. Mucking (muck removal) by loader and trucks, or rail cars.
  8. Temporary support: rock bolts, shotcrete, wire mesh or steel ribs, as per the rock class.
  9. Advancing and repeating the cycle; drainage, services, and survey control.
  10. Final lining: concrete lining, with waterproofing and grouting.
 Drill -> Charge -> Blast -> Ventilate -> Scale
    -> Muck -> Support -> (repeat) -> Lining

Tunnel boring machine (TBM)

A TBM is a machine with a rotating circular cutter head that excavates the whole tunnel section continuously, supports the tunnel with a shield and lining, and removes muck by a conveyor.

Advantages of TBM

  • High speed of advance and continuous operation
  • Smooth tunnel wall and less overbreak, so less lining concrete
  • Safer working and less vibration and ground disturbance
  • Less labour, and consistent quality
  • Suited to long tunnels, with less ventilation problem than blasting

(High cost and long mobilisation time are its limits.)

✓ Answer checked by Claude Opus 5.5 (high effort)

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