---
title: "Tunnel advantages and pressure tunnel section"
subject: "Hydro Power"
chapter: 5
key: "semester_6/hydro_power:tunnel-advantages-pressure-tunnel"
source: https://www.bctengineer.com/q/semester_6/hydro_power/tunnel-advantages-pressure-tunnel
site: BCT Engineering
---

# Tunnel advantages and pressure tunnel section

Hydro Power · Chapter 5: Components of Hydropower System

- Asked in: 2081 Chaitra, 2+2 marks
- Video: [Exploring Hydraulic Tunnels: Shapes, Design, Methods, and Support Structures ⛏️🌊 #tunnel #design#tbm](https://www.youtube.com/watch?v=pI254zTUVE8) — Hydropower
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/tunnel-advantages-pressure-tunnel
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-5

## Question

What are the advantages of tunneling in a hydropower project? Draw a typical cross-section of a pressure tunnel, indicating the key components.

## Short answer

Tunnelsprovide shorter routes, are safe from landslides/floods, carry pressure flow, require low maintenance, cause minimal land disturbance, and rock can share pressure loads in pressure tunnels. A typical pressure tunnel cross-section includes a circular/horseshoe excavation, rock bolts and shotcrete support, concrete lining, grouting, invert, and drainage holes.

## Answer

A **tunnel** is an underground water conductor used as headrace or tailrace in hydropower projects, especially in the steep Himalayan terrain of Nepal.

#### Advantages of tunnelling
1. **Shorter route:** a tunnel can cut straight through a ridge or across a river loop, giving a much shorter waterway than a surface canal following contours (e.g. Kali Gandaki A, Middle Marsyangdi).
2. **Safe from surface hazards:** protected from landslides, rock falls, floods, debris flows and erosion, which often damage surface canals in Nepal.
3. **Can carry pressure flow:** a pressure tunnel allows drawing water from a fluctuating reservoir level and reduces penstock length.
4. **Low maintenance:** no damage from weather, cattle or people; little seepage in good rock.
5. **Environment and land:** minimal land acquisition and surface disturbance.
6. **Good rock carries load:** in sound rock the surrounding rock shares internal water pressure, so lining can be light or omitted.

#### Typical cross-section of a pressure tunnel
```text
        surrounding rock mass
     .  .  .  .  .  .  .  .  .
   .     __________________    .
  .    /  rock bolt  ^       \   .
  .   / /  shotcrete ^  \  \  \  .
 .   | |   concrete lining | | |  .
 .   | |                    | | |  .
 .   | |   water (under    | | |  .
 .   | |    pressure)      | | |  .
  .   \ \                  / /  .
   .   \_\_______________/_/   .
    .  grout   invert  drain   .
      .  .  .  .  .  .  .  .
```
**Key components:**
- **Excavated profile** (circular or horseshoe/D-shape) in rock.
- **Rock support:** rock bolts, wire mesh and shotcrete to stabilise the opening.
- **Lining:** plain or reinforced concrete (steel lining near the powerhouse where cover is low) to reduce friction and leakage.
- **Contact and consolidation grouting** between lining and rock to fill voids and strengthen the rock.
- **Invert** (floor) for construction traffic, and **drainage holes** to relieve external water pressure.

## Check yourself

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

1. A key advantage of tunnelling in Himalayan terrain is:
   A. More landslide exposure
   B. A shorter route cutting through ridges than a surface canal following contours
   C. Bigger land acquisition
   D. Higher cost
   Answer: B. Tunnels go straight through ridges, shortening the waterway. (Key point: Shorter route)

2. Why are tunnels safer than canals in Nepal?
   A. They need more maintenance
   B. They are open to weather
   C. They need no rock
   D. They are protected from landslides, floods and debris flows
   Answer: D. Underground conduits avoid surface hazards. (Key point: Safety)

3. In sound rock, the lining can be light or omitted because:
   A. Velocity is zero
   B. Surrounding rock shares internal water pressure
   C. The tunnel is shallow
   D. Water has no pressure
   Answer: B. Good rock carries part of the internal load. (Key point: Rock sharing load)

4. Contact and consolidation grouting is used to:
   A. Increase friction
   B. Drain water
   C. Excavate
   D. Fill voids between lining and rock and strengthen the rock
   Answer: D. Grouting improves load transfer and reduces leakage. (Key point: Grouting)

## Related in Hydro Power

- [Layout of hydropower scheme components](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Ahydropower-scheme-layout) — Hydro Power, chapter 5
- [Stages of hydropower project study](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Ahydropower-study-stages) — Hydro Power, chapter 3, asked 3×
- [Why settling basins are essential in Nepal](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Asettling-basin-necessity-nepal) — Hydro Power, chapter 5, asked 4×

## Related in other subjects

- [Tunnel importance, components, cross sections](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Atunnel-importance-components-cross-sections) — Transportation Engineering II, chapter 5
- [High dam hydropower project components](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ahigh-dam-components) — Power Plant Design, chapter 3
- [RoR layout: pressure tunnel and free surface](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-layout-pressure-tunnel-free-flow) — Hydropower Engineering, chapter 2
- [Typical cross-sections of hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-cross-sections) — Transportation Engineering I, chapter 5, asked 9×