The Development of Trenchless Technology Systems
Until recently, city administrators and planners believed that the use of construction techniques involving surface trenching was the only option for the construction and repair of utility services. It was assumed that existing services were in good condition unless there was evidence to the contrary. In reality, gradual deterioration went unnoticed and failures occurred without warning, in many cases requiring an urgent response.
Over the last 25 years, it became apparent that little was known about existing utility services. Installation drawings, where they existed, gave little information on pipe capacity or materials used. Furthermore, the condition of the pipe linings was unknown, leakage and infiltration were unmeasured and related health issues were often not addressed.
Applications for new installations
The trenchless sector is continually being refined and developed. Improvements cover both large and small diameters, longer drives, greater accuracy, faster and curve driving, different soil conditions and the ability to work deeper into water tables.
There are many variants of Pipe jacking, during which the product pipe is forced into the ground by hydraulic cylinders mounted horizontal in a launch shaft. The run is completed when the pipe string reaches an exit shaft. Both shafts are used later as service access points. The various systems for new installations can be broadly categorised into:-
Pipe Jacking in which the spoil and water is removed by pumping as slurry
- Guided Auger Boring where the spoil is removed by an auger through a steel casing. Specially designed pipes are then hydraulically jacked in by the machine
- • Pipe Bursting where the existing pipeline is forced into the pipeline bedding by the means of an expanding hydraulic cone controlled from the surface. The new pipe pushes the expanding head through the pipeline which is being replaced
- Pipe Eating where the existing pipe line is ground using a cutting head and the fragments of the pipeline are removed by augers through the new incoming pipe
- Slip Lining where pipes are winched through an existing pipe system and the voids between new system and old system are filled with grout
The Need for Trenchless Technology
Water and sewerage infrastructures have represented a significant asset investment on the part of most municipal organisations and water authorities for well over 100 years. The distribution networks for utility services have been located underground in pipes that are laid, repaired or replaced by trenching from the surface. In cities and urban areas, these distribution networks are located underneath roads. This often makes access difficult, particularly in areas congested with traffic and buildings.
When pipeline infrastructures are not well maintained then inefficiencies arise. For example, in water distribution systems, leakages occur and water shortages are possible. However, in sewerage systems, cracked and damaged pipes can cause wastewater seepage, leading to contamination of groundwater. These problems often give rise to related health and environmental impacts.
The oldest underground utility services are usually found close to the surface. Services installed later are most often found below or interwoven with the initial installations. Construction and repair carried out from the surface inevitably disrupts traffic, business and other services. This disruption has a negative impact on the local environment in terms of air quality, noise and other pollution, as well as on local vegetation and buildings. This in turn diminishes the quality of life for local residents.
Trenchless technologies, which minimise the requirements for surface excavation, can significantly reduce the environmental impacts of underground utility service installation, maintenance and repair. By minimising surface disruption, traffic congestion is significantly reduced.