The Need for Trenchless Techniques
Utilities required for modern day living need to be laid out in a planned manner so that the services being offered- whether, gas, water, electricity, sewerage, or other required conveniences- are able to reach homes, shops and other establishments that have the need for them. Most of these services are accessible from pipes or ducts under the ground on roads and need to be laid continuously, and with necessary stations or manholes for servicing them. While laying such services in newly developing areas is quite easy with properly planned and laid out trenches or service ducts, problems do arise for any modifications or repairs on these lines when areas are already developed. Such replacement and repairs lead to the requirement of trenching that can cause disruption to normal civic life and traffic.
The development of trenchless technology came from the need for reducing this disruption, which quite often also led to unsafe conditions for traffic and people. In this technology a single pit is used instead of a trench and lengths up to 500 meters can be laid without causing any interruption to roads or traffic. Trenchless technology has been used in a number of ways and is basically the technique of renewing, repairing, or installing underground pipes, ducts, or cables without the need for any continuous excavation along the path of the concerned utility.
Some of the technologies use systems that are laser or optically guided to ensure that the services are laid correctly. The basic operation of trenchless technology involves the excavation of a drive pit which houses the equipment needed to bore the openings needed for pipe installation, methods to remove the material that has been drilled into and the equipment needed to push or pull the pipes through the openings so created. A reception pit to which the newly laid pipes are directed is also excavated, and the distance of this pit from the drive pit can be as much as 500 meters. Equipment and techniques will again depend on whether the method requires trenchless construction or trenchless renewal.
Image Source: Flickr: Hachiro-gata, Akita
The Use of Trenchless Technology for Pipe Replacement
Trenchless underground pipe replacement uses a number of different methods to replace damaged pipes or pipes that need replacement. Each of these methods will depend on the actual conditions existing at locations where such trenchless water pipe repair or pipe replacement is required.
Dynamic pipe bursting involves the introduction of a pipe bursting machine winched into the old pipe. Dynamic impact energy is used to destroy the old pipe and the particles created are pushed into the surrounding soil, while the new pipe is then pulled or pushed into the void that has been created.
Another technique is to treat the old pipe and its surroundings as if it were new construction. In this technique, the old pipe is excavated by micro-tunneling and the debris is removed through an auger or bentonite slurry. The new pipe is then pushed into position using hydraulic jacks connected to the back of the shield that has the tunneling equipment.
It is also possible to use the reception pit to hold pipe extraction equipment which will just extract the old pipe while the new pipe is pushed into the void so created from the drive pit.
Image source: Flickr: Wayne Helman
Relining Of Pipes without Trenches
Trenchless pipe relining is relatively easy for larger diameter pipes that can be entered into by workers and can be repaired by lining the damaged surfaces with cement mortar, epoxy spray and other methods. Cured in place pipe lining, or CIPP, is a technique for both renovating pipes and trenchless pipe relining. Though this does lead to a small reduction in pipe diameters, it does produce a structural pipe where the defects, and probably leakages, get permanently sealed.
In this technique a flexible pipe made of a fibrous material is introduced into the pipe to be relined. This pipe has two walls which are filled with a resin that is thermosetting. Once this resin is energized it sets to give a surface to the lining that is structurally watertight and thus able to function as before. Another method is to use thermo-pipes made of polyethylene lining that is reinforced by high tensile polyester. These pipes are not rigid and can be pulled into the damaged pipe. Once it is inserted the pipe is inflated and heated, and it provides the damaged pipe with a structural lining that will function as efficiently as the original pipe material.
Newer techniques constantly being developed in trenchless technology have embraced advancements in hydraulics, plastics, metallurgy and chemicals to find solutions for the problems of installation of pipes and ducts which constantly plague civic authorities.