Tunnel :-
A tunnel can be defined as an underground passage for the transport of passengers, goods, Water, sewage, oil, gas, Etc. The Construction of a Tunnel normally carried out without causing much disturbance to the ground surface.
Size and Shapes of the tunnel :-
The Shapes of tunnel linings are usually determined by their purpose, ground conditions, construction method or lining materials.
Rectangular shape:-
Rectangular shaped tunnel are usually adopted by the cut and cover method. It is particular suitable for pedestrian and highway tunnels. On the other hand, multi-lines submerged highway tunnels are often in rectangular shape.
Elliptical shape / Egg Shape:-
Elliptical shape tunnels are have the advantages for the transportation of sewer. The smaller cross section at the bottom maintains the flow at the required self cleaning velocity. However , due to the difficulty in construction, circular shape once are more common.
Circular shape :-
A circular shape tunnel has the greatest cross-section area to perimeter ratio. They are often associated with TBM or the shield tunnelling methods.
Horseshoe / segmental shape :-
They are commonly used for rock tunnelling. It has the advantages of utilising the compressive strength of concrete in resisting the loading by means of arch action and the base is wide enough for traffic.
