A tunnel building is an underground passage offered beneath earth surface or water. Different methods of tunnel building and their details are discussed.
Large excavation of soil or rock etc. In most of the cases tunnel construction is expensive but it saves time and offers comfort. With the availability of modern equipment, excavation and backfilling has become easier. is necessary for a tunnel construction.
Tunnels can be used for roadways, railways and even as waterways also. In many cities, underground metro rail networks work inside a tunnel.
There are various types of construction techniques developed for construction of tunnels which are discussed below:
Cut and cover approach of tunnel construction is generally used to build shallow tunnels. In this approach, a trench is cut in the soil and it is covered by some support which can be capable of bearing load on it.
One is bottom up method in which a tunnel is excavated under the surface using ground support. The cutting can be done by two methods. Another method is top-down method in which side support walls are constructed first by slurry walling method or contiguous bored piling.
Then roof is located on the top of the walls and excavation is carried out. Most of the Underground metro rail stations are constructed using cut and cover approach. Finally, base slab is constructed.
Bored tunnel approach is modern technology. It is also quicker procedure and good approach to build tunnel in high traffic areas. In this case, tunnel boring machines are used which automatically work and makes the entire tunneling procedure easier.
Tunnels boring machines (TBM’s) are available in different types suitable for different ground conditions. These machines can be used in difficult conditions such as below the water table etc.
A special pressurized compartment is provided for TBM to work in below water table conditions. The laborers should not enter that compartment except for repair works.
Care must be taken while TBM is in working conditions. The only difficulty with this TBM is its heavy weight. So, transportation is difficult and costlier.
This method is used for strong clayey soil conditions. This is an old method and used for small works like sewage pipes installations etc.
In this method, a hole is excavated into the ground and after some depth tunnel is excavated which is done by the clay kicker which lies 0n a plank at 45 o angle.
An excavating tool is provided under clay kicker foot. This is well famous because it is the approach used by Englishmen to put mines under the German empire during First World War. The excavated using that tool is collected by other laborers.
In this approach tunnel is constructed at greater depth from the ground surface. The shaft is built up to the depth where tunnel is required.
Shaft is a permanent structure which is like well with concrete walls. At needed depth, tunnels are excavated using TBM’s. Shafts are offered at both inlet and outlet of tunnels.
Intermediate shafts are also provided if tunnel is too long. After the construction process, these shafts can also be used for ventilation purpose as well as emergency exits.
Pipe jacking method is used to construct tunnels under existing structures like road ways, railways etc. Maximum size of 3.2-meter diameter is allowed for tunnels. In this method, specially made pipes are driven into underground using hydraulic jacks.
Box jacking approach is similar to pipe jacking, but in this case instead of pipes, specially made boxes are driven into the soil. A cutting head is provided at the front side of the box. Larger size tunnels can be excavated using box jacks up to 20 meters. Excavated matter is collected within the box.
An underwater tunnel is a framework which is built under water to make a way through it. If building of bridge is not possible then under water tunnel is good choice.
Under water tunneling is costly process but have advantages over bridge or ferry links. Immersed tubes or bored tunnel are two most common approaches which are used to construct under water tunnels.
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