Different Shape of Tunnels
Commonly used tunnel shapes are discussed below:
- Horseshoe type
1. Polycentric Shaped of Tunnels
This sort of tunnel shape has a number of centers and provides a sufficient flat base for traffic movement.
- It can be used for road and railway traffic.
- It can resist external and internal pressure for their arch shape.
- The construction of these tunnels is difficult.
- The lining of this type of tunnel is difficult.
2. Circular Shaped Tunnels
Circular tunnels are used to carry water under pressure. These are not appropriate for traffic tunnels because more filling is needed to make the base flat.
- Best to resist the external or internal force.
- It provides the greatest cross-sectional area for the least perimeter.
- More filling is required to form a flat base for designing a road or railway track.
- In circular tunnels, lining work is very difficult.
3. Rectangular Shaped Tunnels
For pedestrian tunnels, rectangular shapes of tunnels are appropriate. These tunnels are sometimes accepted if pre-constructed R.C.C caissons are used. This types of tunnels not suitable to resist external pressure due to their rectangular shape and these are not in use these days.
4. Egg Shaped Tunnels
This tunnel shape has a number of centers and radius length. These are suitable as sewer tunnels to carry sewage water.
5. Horse Shoe Type Tunnels
Horseshoe type tunnel shape is a combined shape of arches and circular tunnel. These type of tunnels shape is quite popular.
6. Elliptical Shaped Tunnels
For carrying water, elliptical-shaped tunnels are appropriate. These are suitable in softer material. For better resistance to external pressure, the major axis of these tunnels is maintained vertically.
These are appropriate as traffic tunnels. These are generally used for subway or navigation tunnels.