---
title: "Methods of tunnel excavation"
subject: "Construction Management"
chapter: 4
key: "semester_8/construction_management:tunnel-excavation-methods"
source: https://www.bctengineer.com/q/semester_8/construction_management/tunnel-excavation-methods
site: BCT Engineering
---

# Methods of tunnel excavation

Construction Management · Chapter 4: Familiarization with Construction Equipments

- Asked in: 2071 Bhadra, 6 marks
- Video: [Tunnel Class 1    • Tunnel construction methods. New Austrian Tunneling Method (NATM)](https://www.youtube.com/watch?v=L50POQT2CEQ) — CIVIL ENGINEERING BAWAA
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/construction_management/tunnel-excavation-methods
- Whole chapter: https://www.bctengineer.com/md/semester_8/construction_management/chapter-4

## Question

Discuss the methods of tunnel excavation.

## Short answer

Tunnel excavation methods include drilling and blasting for hard rock, mechanical excavation by TBM or roadheader, heading and bench for large sections, soft-ground methods like shield, pipe jacking, cut-and-cover and NATM, plus multiple drifts and ripping. The choice depends on geology, tunnel size and length, water inflow, equipment, schedule and cost.

## Answer

Tunnel excavation methods depend on the type of ground, the size and length of the tunnel, time, and cost.

#### 1. Drilling and blasting (drill and blast)
Holes are drilled in the face, charged with explosives and blasted; the muck is removed and the roof is supported. Used in hard rock; flexible for any shape. Steps: drilling, charging, blasting, ventilation, mucking, scaling and support.

#### 2. Mechanical excavation
- **TBM (full face):** a rotating cutter head cuts the whole section and the muck is carried away by conveyor. Fast and safe for long tunnels.
- **Roadheader:** a boom-mounted cutting head for soft to medium rock and for tunnels of variable shape.

#### 3. Heading and bench method
The tunnel is excavated in two stages: a top heading first (which is supported), then the bench below. Used in large sections.

#### 4. Soft-ground methods
Shield tunnelling, pipe-jacking or micro-tunnelling, cut-and-cover (open trench, then roof), and the New Austrian Tunnelling Method (NATM) with shotcrete and rock bolts.

#### 5. Other methods
Multiple drifts (side drift, centre drift), and excavation by ripping or hydraulic breakers.

Choice factors: geology and rock quality, tunnel length and diameter, water inflow, available equipment, and the schedule and cost. Support (rock bolts, shotcrete, steel ribs) follows each method to keep the opening stable, and the lining is built afterward.

## Check yourself

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

1. What is the order of steps in drill and blast?
   A. Drilling, charging, blasting, ventilation, mucking, scaling and support
   B. Support, blasting, drilling
   C. Mucking, drilling, charging
   D. Blasting, drilling, charging
   Answer: A. The cycle starts with drilling and charging, then blasting, ventilation, mucking, scaling, support. (Key point: Drill and blast steps)

2. What is the heading and bench method?
   A. Whole face at once
   B. Bottom first
   C. Using a TBM
   D. Top heading excavated and supported first, then bench below
   Answer: D. It is two-stage excavation for large sections. (Key point: Heading and bench)

3. Where is a roadheader suited?
   A. Soft ground only
   B. Underwater only
   C. Soft to medium rock and variable shapes
   D. Hardest rock only
   Answer: C. Roadheaders cut soft to medium rock. (Key point: Roadheader)

4. Which is a soft-ground method?
   A. Heading only
   B. Shield tunnelling or NATM
   C. Drill and blast
   D. Gripper TBM
   Answer: B. Soft-ground methods include shield tunnelling, pipe-jacking, cut-and-cover and NATM. (Key point: Soft-ground methods)

## Related in Construction Management

- [Short note: Tunnel excavation by blasting](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atunnel-blasting-note) — Construction Management, chapter 4