---
title: "Conventional tunnelling steps and TBM advantage"
subject: "Construction Management"
chapter: 4
key: "semester_8/construction_management:tunnelling-conventional-tbm"
source: https://www.bctengineer.com/q/semester_8/construction_management/tunnelling-conventional-tbm
site: BCT Engineering
---

# Conventional tunnelling steps and TBM advantage

Construction Management · Chapter 4: Familiarization with Construction Equipments

- Asked in: 2078 Chaitra, 7 marks
- Video: [Conventional Methods of Tunneling - Equipment for Underground and Underwater Tunneling](https://www.youtube.com/watch?v=1YWkHd3hZ0I) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/construction_management/tunnelling-conventional-tbm
- Whole chapter: https://www.bctengineer.com/md/semester_8/construction_management/chapter-4

## Question

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.

## 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.

## Answer

#### 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.

```text
 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.)

## Check yourself

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

1. Which comes immediately before blasting?
   A. Charging the holes with explosives
   B. Mucking
   C. Lining
   D. Scaling
   Answer: A. Drilling, then charging, then blasting. (Key point: Order of steps)

2. What is scaling?
   A. Measuring
   B. Drilling
   C. Lining
   D. Removing loose rock from roof and sides
   Answer: D. Scaling removes loose rock after blasting and ventilation. (Key point: Scaling)

3. Which is an advantage of TBM?
   A. Short set-up
   B. Easy diameter change
   C. Fast continuous advance, smooth wall and less overbreak
   D. Low cost
   Answer: C. TBMs give speed and smooth walls, less lining concrete. (Key point: TBM advantage)

4. What is a limit of TBM?
   A. More labour
   B. High cost and long mobilisation time
   C. Slow advance
   D. More vibration
   Answer: B. High cost and long mobilisation are its limits. (Key point: TBM limit)

## 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×
- [Pre-qualification steps vs post-qualification](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Aprequalification-steps-post) — Construction Management, chapter 5
- [Short note: Tunnel boring machines](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atunnel-boring-machine-note) — Construction Management, chapter 4, asked 3×
- [Methods of tunnel excavation](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atunnel-excavation-methods) — Construction Management, chapter 4
- [Short note: Tunnel excavation by blasting](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atunnel-blasting-note) — Construction Management, chapter 4
- [Detailed specification of brick work in 1:4 mortar](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Adetailed-spec-brick-1-4) — Construction Management, chapter 12, asked 5×

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