Different 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:
- Cut and cover method
- Bored tunnel method
- Clay kicking method
- Shaft method
- Pipe jacking method
- Box jacking method
- 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.