Methods of Tunnelling | Uses
Methods of tunnelling:
Because paleontological and structural variations are common in nature, ground surface and subsurface excavation depend on factors such as the geology of the area, groundwater level, and depth of excavation.
The basic types of tunnel construction are cut and cover and boring. When making the cut and cover type tunnels Built-in shallow trenches and then covered, tunnels have been built in situ without removing the top.
Deep tunnels are excavated, usually using a tunnel shield. Some methods of tunneling
Described below.
Cut and cover method
This is also known as the traditional method of tunneling and is suitable for the construction of shallow tunnels. Most tunneling projects are made more practical and economical by this method.
In this method, a trench is excavated and its roof is covered with an overhead support system strong enough to carry the load required to be built on the tunnel. Two basic forms of cut and cover
Subways are the bottom-up method and the top-down method (Figure 9.16).
Metro tunnels in New Delhi are an example of the cut and cover method of the tunnel.
Bottom-up method
A trench is excavated from the surface. After reaching the final depth, the tunnel floor is built. Then the walls and ceilings are built. The tunnel may be in situ concrete, precast concrete, precast arches or corrugated steel vaults; In the early days, brickwork was used. Finally, the trench is replenished and the surface is restored.
Top-down method
The side-support walls and capping beams are first constructed from the ground level in this manner. Then the shallow excavation allows the roof of the tunnel to be made. The surface is then restored except for the entrance Openings.
This allows minimal interruption of roadways, services, and other surface features. Then the excavation takes place under the roof of a permanent tunnel and a base slab is built.
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Tunnel Drilling Machine (TBM)
This machine is characterized by a circular cutter head with an array of suitable cutters. Rotation and translational movement of the cutter takes place between 1 and 3 rpm. Foam or slurry is used on the face of the machine so that it is cool to work with.
The hydraulic system has a built-in feature in this machine. The pressure exerted by the TBM on the soil or rock is significantly lower than the blasting. This method is very suitable for driving long tunnels in mountainous areas where the geological profile is stable.
There is no overlap in large-diameter tunnels and therefore the loss of land is very low.
Example: TBM is being used for the construction of the second phase of the Delhi Metro (Figure 9.17).
Soil kicking method
Clay-kicking is a special technique developed to manually dig tunnels in strong, clay-based clay structures. This method is suitable for the construction of small tunnels. This is the fastest and least expensive method. In this method of tunneling, the clay-kicker sits on the board 45 ° away from the working face.
The grafting apparatus has flat, soft soil at the base and an arrow-like structure. Tunnels are excavated in the types of materials that vary from soft clay to hard rock.
The method of tunnel construction depends on factors such as ground conditions, groundwater conditions, tunnel length and diameter, tunnel depth, and logistics supporting tunnel excavation and end-use.
Uses of the tunnel:
Some of the specific uses of tunnels are pipelines for logging, mining, water supply, oil and gas transport, and secret tunnels for defense purposes.
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