What are Tunnels?

The branch of civil engineering which deals with the design, construction and maintenance of tunnels is known as tunnel engineering.

Therefore the underground passages which are constructed without disturbing the ground surface are known as tunnels.

Uses of Tunnels:

1. Firstly one uses it for transportation of men, materials and goods.
2. Therefore tunnels are used for conduction of water to generate power.
3. Lastly they are used for carrying oil, sewage, gas etc.

Necessity :

1. When the two terminal stations, separated by a mountain, are to be connected by the shortest route and depth of open cut for reaching the other side of a hill is more than 20 m, it is considered to construct and maintain it more than a tunnel.
2. When one avoids acquisition of valuable land and property for a railway or road project.

Advantages:

1. They connect the two terminal stations by the shortest route and less route length thus result in less transportation cost.
2. Therefore they facilitate conduction of water to generate power.

Disadvantages:

1. Firstly they require specand method for their construction.
2. therefore tunnels require more time for their construction.
3. One requires Skilled labour and supervision in their construction
4. Lastly they may cause suffocation if not properly ventilated.

Classification of Tunnels:

1. Classification based on purpose

A. Traffic:

1. Railway
2. Highway
3. Pedestrian
4. Navigation
5. Subway

B.   conveyance:

1.  Hydro power

 2. Water supply 

 3. sewage

2. Classification based on types of material

1. Hard rock
2. Soft rock
3. Tunnels in quick sand
4. Under river bed

3. According to position or alignments.

1. Saddle and bade 
2. Spiral
3. Off spur
4. slope

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