Different Tunneling Methods

Tunneling methods

Since tunneling projects are one of the most challenging geotechnical projects, different construction method have been developed. Here are some widely used methods to construct a tunnel:

1. Cut and cover method
2. Bored tunnel method
3. Clay kicking method
4. Shaft method
5. Pipe jacking method
6. Box jacking method
7. Underwater tunnels

 

Cut and cover method is highly effective to construct shallow tunnels. In this method a trench is excavated and covered by a stiff roof to support the loads.

In this method, cutting of the trench can be carried out by two methods. In the first method, a tunnel is excavated under the surface using ground support, while in the another approach, called top-down, soil excavation is started from the ground surface and two side support walls is constructed progressively to provide a safe condition for excavation. Once the trench is cut, the ceiling is constructed on the top of the walls.

1. Tunnel boring machines

• A tunnel boring machine (TBM)  is a machine powerful machine used to excavate cylindrical tunnels through a different soil materials. This method can be performed for a wide range of materials including hard rock and sand. TBM is designed and manufactured for different diameter of the cross section from 1 to 15 metres. For smaller diameters horizontal directional drilling is more common due it its lower cost.

• In comparison with drilling and blasting (D&B) of rocks, TBMs is more advantageous in terms of lower disturbance and production of a smoother tunnel wall, resulting in a cheaper lining operation of the walls.
• On the other hand, construction and transport of TBMs are significantly expensive, which is why TBMs are reasonable only for long tunneling projects.

2. Immersed Tunnels

• Immersed tunneling is a method during which pre-fabricated segments are installed under water to shape the body of a concrete tunnel. Once the installation process has been completed, the joints are sealed to make the walls water resistant.

3. Box jacking method

• In Box jacking method, which is a non-disruptive technique, cast concrete box structures are installed using high capacity hydraulic jacks.
• The main advantage of tunnel jacking method is for construction sites that cannot be blocked by open-cut excavations., since this technique avoids disruption of adjacent infrastructures.As a result the servicibility of above infrastructures is not going to be interrupted.