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

# Short note: Tunnel excavation by blasting

Construction Management · Chapter 4: Familiarization with Construction Equipments

- Asked in: 2070 Bhadra, 4 marks
- Video: [Orica Case Study: Managing blast vibration whilst increasing tunnel advance rates](https://www.youtube.com/watch?v=F16e2U7MRGc) — Orica
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/construction_management/tunnel-blasting-note
- Whole chapter: https://www.bctengineer.com/md/semester_8/construction_management/chapter-4

## Question

Write a short note on 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.

## Answer

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.

```text
   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.

## Check yourself

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

1. What do cut holes do?
   A. Open the face first
   B. Smooth the profile
   C. Lift floor
   D. Enlarge only
   Answer: A. Cut holes open the face; easers enlarge; contour holes smooth; lifters floor. (Key point: Cut holes)

2. What are contour holes for?
   A. Opening the face
   B. Floor
   C. Ventilation
   D. Smooth blasting for a clean profile
   Answer: D. Contour (perimeter) holes give a clean profile. (Key point: Contour holes)

3. Which is a limit of blasting?
   A. Inflexible
   B. Slower never
   C. Overbreak, vibration, fumes and noise, needs strict safety
   D. Needs costly TBM
   Answer: C. It causes overbreak, vibration, fumes, noise and is slower than TBM. (Key point: Limits)

## Related in Construction Management

- [Methods of tunnel excavation](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atunnel-excavation-methods) — Construction Management, chapter 4