---
title: "Short note: Tunnel boring machines"
subject: "Construction Management"
chapter: 4
key: "semester_8/construction_management:tunnel-boring-machine-note"
source: https://www.bctengineer.com/q/semester_8/construction_management/tunnel-boring-machine-note
site: BCT Engineering
---

# Short note: Tunnel boring machines

Construction Management · Chapter 4: Familiarization with Construction Equipments

- Asked in: 2067 Mangsir (old course), 4 marks; 2066 Magh (old course), 4 marks; 2064 Poush (old course) (asked 3 times)
- Video: [Making Way for the Mega Machine (Alice TBM)](https://www.youtube.com/watch?v=U_qGHBM66Nk) — Waterview Connection
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/construction_management/tunnel-boring-machine-note
- Whole chapter: https://www.bctengineer.com/md/semester_8/construction_management/chapter-4

## Question

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

## 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.

## Answer

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.

```text
   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).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is a TBM's main feature?
   A. Needs explosives
   B. Excavates only the top heading
   C. Is hand operated
   D. Excavates the full circular section continuously without drilling and blasting
   Answer: D. A TBM excavates the whole circular section mechanically without blasting. (Key point: TBM basic)

2. What do the thrust rams do?
   A. Remove muck
   B. Mix grout
   C. Rotate the cutter
   D. Push the machine forward against the lining or grippers
   Answer: D. Thrust rams push the machine forward against lining or grippers. (Key point: Thrust rams)

3. Which TBM types suit soft, wet ground?
   A. Roadheader only
   B. Open gripper TBM
   C. EPB and slurry TBM
   D. Hand TBM
   Answer: C. EPB and slurry TBMs suit soft, wet ground; gripper TBM suits good hard rock. (Key point: Soft wet ground TBM)

4. When is a TBM economical?
   A. For very short tunnels
   B. For long tunnels, usually over 3-5 km
   C. Only in surface cuts
   D. When alignment will change often
   Answer: B. High cost makes TBMs economical only for long tunnels. (Key point: TBM limitation)

## Related in Construction Management

- [Tunnelling and rock drilling equipment](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atunnel-rock-drilling-equipment) — Construction Management, chapter 4, asked 3×