A tunnel system is an underground path created beneath the surface of the earth or underwater. Specific tunnel design techniques and their specifics are explored. Tunnel building is costly in most situations but it saves time and offers convenience. Broad soil or rock excavations etc. are needed for the construction of a tunnel.
Table of Contents
Methods of Tunnel Construction
- Shaft method
- Pipe jacking method
- Clay kicking method
- Cut and cover method
- Box jacking method
- Bored tunnel method
Shaft Method of Tunnel Construction-In this approach tunnel is built from the ground surface at a greater depth. The shaft is designed to the level where it includes tunnels.
The shaft is a fixed framework of concrete walls that are as good. Tunnels are excavated at the appropriate distance, using TBM’s. Shafts are supplied at both tunnel inlet and outlet. In the case the tunnel is too long, intermediate shafts are also provided. These shafts may also be used for ventilation purposes after the construction process as well as for emergency exits.
Pipe Jacking Method -The pipe jacking technique is used to construct tunnels beneath established infrastructure such as roadways, railways, and so on. In this method, hydraulic jacks are used to drive specially made pipes into the underground. Tunnels are allowed to have a maximum size of 3.2 m in diameter.
Cut and Cover Method -Tunnel construction methods are generally used to cut and cover for the construction of shallow tunnels. A trench is cut in the soil in this method, and it is covered by some support that can bear the load on it. The cutting may be carried out using two methods. One is a bottom-up method in which the ground support is used to excavate a tunnel under the surface. Another method is the top-down method in which side support walls are built first by the method of slurry walling or contiguous bored piling.
Then the roof is on top of the walls, and excavation is performed. The base slab is finally built. Most underground metro stations are designed using the system of cutting and shielding.
Clay Kicking Method of Tunnel Construction-This method is applied to conditions of strong clayey soil. This is an old method and is used for small works such as installations of sewage pipes etc.
A hole is excavated into the ground in this method and after some depth tunnel is excavated, which is done by the clay kicker which lies at an angle of 45o 0n a plank.
Bored Tunnel Method-The bored tunnel method is cutting-edge technology. In this case, tunnel boring machines are used which function automatically and simplify the entire tunneling process. The construction of tunnels in high-traffic areas is often faster operation and successful tool. Tunnel boring machines (TBM’s) are available in numerous forms to match specific ground conditions. Such devices may be operated in challenging circumstances like underwater tables etc.
TBM is fitted with a special pressure compartment to operate in conditions below the water level. Except for repair works the workers should not enter that compartment.
While TBM is in working conditions, care should be taken. The only difficulty is the heavyweight of this TBM. So, it is harder and more costly to ship.
Box Jacking Method -The box jacking method is similar to pipe jacking, but in this case, the specially made boxes are driven into the soil instead of pipes. At the front of the package is given a cutting handle. Excavated material is gathered inside the box. Larger tunnels can be dug with box jacks of up to 20 meters.
Tunneling is one of the most complex and complicated buildings and development tasks. With growing demands and the focus on raising travel time between any two locations being a priority, the dangers and difficulties associated with tunnel development have increased.
The concept of tunnels was first implemented in the year 1843 when the first underwater tunnel was built to connect the River Thames’ north and south bank in London. It is still considered a financial failure after much hardship and a series of failures, although the tunnel was successfully built.
Types of Tunnel Failure & Causes:
1. Improper Blasting Methods
Reasons for Improper Blasting-Due to the expense factor involved in shipping TBM and improving the current transportation infrastructure, it is impossible to maintain the tunneling phase using Tunnel Boring Machines (TBM) during the building of a tunnel in mountainous areas. The alternate solution is then introduced, including the use of blasting for the cut and cover process.
If the blasting is not built properly, it will trigger the rock mass to compress and break, which will ultimately contribute to the tunnel to collapse entirely.
Corrective Measures-The blasting device will be configured to integrate all the technical parameters such as charging, stemming frequency, bench width, fly rock power, and so on.
2. Wrapping and Twisting of Tunnel Aid Program
Reasons for Wrapping and Twisting-Due to the constant entrance of water to the bottom of the tunnel portal, the bearing ability of ground soil below the portal reduces, allowing the concrete lining to sink into the ground and contributing to the wrapping and twisting of the tunnel support structure.
Corrective Measures-The portion that is subjected to the maximum stress point is the inverting stage of the tunnel; therefore, a systematic approach should be taken in designing the drainage scheme to protect the invert.
3. Land Collapse near the Tunnel Portal
Trigger for Ground Collapse-The reason the ground below the tunnel portal fell is due to the extreme build-up of pore water pressure, which may be related to heavy rainfall.
Corrective Measures- It is necessary to follow the umbrella strategy that preserves the material covering the tunnel diameter and reduces the risk of sudden collapse.
4. Presence of areas of instability and fracture
Reasons for Fault and Fracture Zones-The faults and fractures are loosened due to the blasting process, and then the loosened rock mass generates an undue shear force on the edge of the current pipe and may trigger shear failure and cracks in the concrete lining.
Corrective Measures-If any major defect or cracks are found during the building of a tunnel, then the tunnel orientation will be modified instead of continuing with the same orientation. If alignment can not be changed due to unexpected circumstances, rather appropriate measurement equipment should be used to map the direction of the fault.
5. Cavity Shape
Reasons for Cavity Formation-After the blasting process is full, cavities will create rock mass in the surrounding area. If the cavity evaluation of tunnel alignment is not done until each and every trail is progressed, instead the tunnel failure near the front portal may result in an increase in the risk of the accident.
Corrective Measures-Trail holes will be created before each and every progress in the tunnel segment and if any gap is found it should be filled with a slurry of bentonite.