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Short note: Tunnel boring machines

Short answer

A TBM excavates a full circular tunnel continuously without blasting. Main parts are cutter head, shield, thrust rams, muck conveyor and segment erector. Types include open, shielded, EPB and slurry TBMs. Advantages: fast, safe, smooth surface; disadvantages: high cost, long setup, only economical for long tunnels.

Write a short note on tunnel boring machines (equipment for tunnel boring).

A tunnel boring machine (TBM) excavates a full circular tunnel section in a continuous mechanised operation, without drilling and blasting. It is used for long tunnels in hydropower, metro, water supply and road projects.

   cutter head   shield     erector    conveyor
   [O|O|O]======[=========][segment]=======>  muck out
     ^ rotates   thrust rams push on lining

Main parts

  • Rotating cutter head with disc cutters (hard rock) or teeth/scrapers (soft ground)
  • Shield that protects the crew and supports the ground
  • Thrust rams, which push the machine forward against the installed lining or grippers
  • Muck removal conveyor
  • Segment erector to build the precast concrete lining
  • Control cabin, grout and ventilation systems

Types

Open (gripper) TBM for good hard rock; shielded TBM for fractured rock; earth pressure balance (EPB) and slurry TBMs for soft, wet ground; double-shield TBM.

Advantages and disadvantages

Advantages: fast and continuous advance, smooth tunnel surface, less overbreak, safe working, less vibration, and less labour. Disadvantages: very high initial cost, long delivery and set-up time, difficulty in changing the alignment or diameter, and it is economical only for long tunnels (usually a few kilometres or more).

✓ Answer checked by Claude Opus 5.5 (high effort)

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