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Most of the Underground metro rail stations are constructed using cut and cover method. Bored tunnel method is modern technology. In this case, tunnel boring machines are used which automatically work and makes the entire tunneling process easier. It is also quicker process and good method to build tunnel in high traffic areas. 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 workers should not enter that compartment except for repair works. Care should 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. The excavated using that tool is collected by other workers. This is well famous because it is the method used by Englishmen to put mines under the German empire during First World War.
In this method 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. Shafts are provided 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. In this method, specially made pipes are driven into underground using hydraulic jacks. Maximum size of 3. Box jacking method 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. Excavated matter is collected within the box.
Larger size tunnels can be excavated using box jacks up to 20 meters. An underwater tunnel is a structure which is built under water to make a way through it. If construction 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 methods which are used to construct under water tunnels. Sign Up Sign Up to The Constructor to ask questions, answer questions, write articles, and connect with other people. Have an account? The Ramsgate tunnel was constructed almost entirely in good quality chalk.
It only encountered brick earth in the soffitt from a belly feature at one prevault and after extensive ground investigations. Crow said that this had been plotted to within a few metres. Other hazards in the ground have also been encountered during the bore, including numerous faults, man-made caves built to hide smugglers, and of course the usual scattering of solution features common to chalk.
The Ramsgate tunnel was constructed almost entirely in good quality chalk. It only encountered brick earth in the soffitt from a belly feature at one prevault and after extensive ground investigations. Crow said that this had been plotted to within a few metres. Other hazards in the ground have also been encountered during the bore, including numerous faults, man-made caves built to hide smugglers, and of course the usual scattering of solution features common to chalk.
But Newman explained that the Perforex system allows tunnelling to advance by as little as mm to increase the prevault overlap to as much as 4. Sign in or Register a new account to join the discussion. Chainsaws at the chalkface. Anthony Oliver. Infrastructure Insight Summer The fourth of our special reports aimed at helping civil engineers understand….
Pneumatic pipe ramming uses the power of compressed air to drive piping or pipe casings into the ground. The process uses successive blows of a rammer to strike the rear of the pipe. A soil cutting shoe is attached to the leading edge of the pipe casing with a sharp edge to penetrate the soil. Sometimes lubricant like bentonite is also used to facilitate the cutting of the soil and the sliding of the pipe casings behind the cutting edge. The rear end of the pipe casing, which takes the force of the rammer blows, is protected by an adapter.
Soil is removed by auger boring, water jetting or compressed air, depending on the size of the pipe bore. Pneumatic pipe ramming is suitable for pipes being laid in a straight line, in shallow ground. The ramming process can also be used with other tunneling methods in order to loosen a pipe that is stuck. For more on pipe ramming, see The Process of Pipe Ramming. As the name implies, guided boring is used to control the path of a pipe through the ground to a high degree of accuracy.
Specialized laser guiding equipment guides the drill along the predetermined path to an accuracy of within one inch. Guided boring is a two-step operation. First, a pilot tunnel is drilled along the precise path required. The direction of the drill is controlled using slanted or asymmetrical drill heads or movable fluid jets in the drilling head.
Once the pilot bore is complete, a back reamer enlarges the diameter of the hole to accommodate the piping. Guided boring is an expensive option due to the complexity of the laser guiding equipment and skilled personnel required to use it. Down the hole hammers are designed to solve problems of hard rock encountered during trenchless tunneling. Sometimes a horizontal directional drilling machine encounters a section of rock that it cannot penetrate. Rather than damage drilling heads by excessive force and wear, construction crews use a down the hole hammer to solve the problem.
This equipment is like a jackhammer often seen on the side of the road as construction crews break through road surfaces or concrete. It is pneumatically powered to deliver hammer blows, driving the hammer into the rock. Because it is attached to the drill string , it also uses the rotational force of the drill to add to the force. Compressed air blows the rock chips and dust away from the cutting surface. Down the hole hammers are used along with other tunneling methods to break up hard rock that is preventing the job from being completed.
Slip boring is a process that uses a pipe casing to make the initial penetration through the earth. Product pipe segments are welded to the rear end of the pipe casing and pulled or pushed into the bore as it progresses. The advantage of this technique is that the product casing takes up most of the force associated with creating the bore, thus protecting the product pipes from excessive stress.
Once the pipe casing emerges at the exit pit , it is cut off from the product pipe, and the job is complete. This technique is helpful when engineers are concerned about the integrity of the product pipe due to the forces of pipe ramming or other trenchless methods. Surface casing or pipe casings can be used with a variety of trenchless methods. The idea behind this technique is to use the tunneling process to install a continuous casing.
Once the casing is in position, the product pipe is inserted inside the casing. Using surface casings is expensive because of the material costs, but the resultant installation offers a lot of protection for product pipes. They are not exposed to the stresses of the tunneling itself and they are also protected in the future against excavations that may damage the pipes.
Tunnel boring and pipe jacking use hydraulic jacks to push segments of piping into a bore, while a tunnel boring machine excavates the soil for removal from the entry pit. The tunnel boring machine has a combination of cutters to excavate the soil as the pipe progresses through the bore.
This technique can be used for any type of ground conditions and is especially useful for pipes being laid in a straight line through rocky and complex soil conditions. Trenchless construction with its various tunneling methods is changing the laying and maintaining of underground pipes and utilities for the better.