Classification of tunnels
The tunnels are classified into,
- According to alignment
- According to purpose
- According to the type of material met with at the time of construction
- According to the shape of tunnels
We are going to read each of this classification in this article
- Types of tunnel according to alignment
1. Offspur Tunnel
Short length tunnels to negotiate minor local obstacles, which cannot be followed with permitted curves.
2.Saddle or base tunnel
These are constructed in the valleys along the natural slope. They are mainly constructed for the transportation purposes. Railway tracks and roads can be constructed through these saddle tunnel.They are one of main types of tunnel for transportation.
3.Slope tunnel
These include the tunnels that are constructed in steep hills. These types of tunnel are also used for transportation purposes.
4.Spiral tunnels
- These include the tunnels that are provided in narrow valleys in the form of loops in the interior of the mountain.
This increases the length of the tunnel to avoid the steep slopes.
- CLASSIFICATION ACCORDING TO THE PURPOSE
1.Conveyance tunnels
- These types of tunnel includes the sewer tunnels, water supply tunnels, hydro-electric power tunnels etc.
2.Water conveyance tunnel
3.Traffic tunnels
- They include highway tunnels, railway tunnels, pedestrian tunnels, navigation tunnels and subway tunnels.
- Tunnels in hard rock.
- Tunnels in soft materials.
- Tunnels underneath river bed or in water-bearing soils.
Classification according to shape of tunnels
1.D shaped tunnel
- Where the risk of failure or collapse caused by external pressure from water or loose unstable soil conditions on tunnel lining is non-existent
- These types of tunnel roof also called segmented roof takes up all the load and distributes it to the straight walls
- Suitable for subways
D shaped tunnel
2.Circularly shaped tunnel
- This shape of tunnels is strong in offering resistance to external pressure caused by water, water-bearing soils or soft grounds
- Not suitable for rails and roadways as more filling will be required to provide a flat base
- For tunnels which may have to withstand heavy internal or external radial pressures
- Used as a sewage pipeline, to transport oil etc
Strongest and economical – having more cross-section and least perimeter
3.Horseshoe-shaped types of tunnel
- Having a semi-circular rood with arch sides
- Commonly used in railways and roadways
- Can withstand the internal and external pressure
- Combines the advantages of D shaped and circular tunnels
4.Rectangular shaped tunnel
- Rectangular types of tunnels are suitable for hard rocks
- Suitable for pedestrian passage
- costly
5.Egg-shaped tunnel
- Egg-shaped types of tunnels are best suited for sewage line as it is having a self-cleaning velocity in dry weather
- Egg shaped tunnel can resist both internal and external pressure
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