Trenchless tunneling is a method of repairing or installing pipelines or cables under streets or buildings, without disturbing structures on top. This system has evolved as a result of alternative methods that were being put into action by engineers to rehabilitate structures under the streets.
This method is often put to use in big cities, especially for busy streets. It mainly resorts to methods like tunneling, micro tunneling, horizontal drilling, pipe ramming, jacking, and horizontal auger boring. The process of rehabilitating or constructing structures with the help of trenchless tunneling is not very difficult.
In the process of construction, two pits are dug between which the pipeline or cable is to be placed. The first pit is termed as the 'intersection pit' and the second is termed as the 'reception pit'. A device similar to a mechanical mole is inserted in the intersection pit. The mole drills a tunnel till it reaches the reception pit. The drilled dirt and rubble is then removed by a device that works like an excavator.
This process of tunneling is often referred to as micro tunneling. The coil and loop of a winch or a puller is passed from the reception pit to intersection pit. The pipeline or cable that is to be laid is made up of flexible and sturdy material. The coil of the puller is attached to the end of the cable and is inserted in the tunnel. The puller reverses and pulls the cable or pipeline till it reaches the receiving pit. After it has been suitably laid down, a miniature concrete chamber is created in both pits.
In case of repairs, the pulling machine first extracts the damaged cable, and then a new one is placed in the micro tunnel. If a pipeline is to be removed, then an excavating machine, known as 'bursting head', first removes the debris of the broken pipeline and then a new one is placed inside.
Some of the other methods that are deployed include slip-lining, and mechanical spot recovery, where the whole pipeline is not replaced, but only the damaged section is repaired. Another method that is used is shotcrete, in which spot leaks or cracks in the pipeline are repaired with the help of concrete or a sealing material shot inside the pipeline through a pressurized hose.
Advantages of Trenchless Technology
The biggest advantage of this method is that it does not disrupt traffic, as done in normal construction methods in which a trench is dug up for repair. Trenchless tunneling is also efficient in saving resources, as the street that is dug up does not have to be repaired or reconstructed. It is also a very simple process that does not involve complex techniques and highly skilled man power. The construction work also does not take a long time, and is completed easily and quickly.
This technology is slowly coming to prevalence due its many merits, however, the equipment that is used is still costly.