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 installation 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 the pipes are winched through an existing pipe system and the voids between new system and old system are filled with grout.
Financial Considerations
In addition to environmental and social factors, financial comparisons can be made between Trenchless Technologies and traditional open cut methods. However, these comparisons are often difficult because there are no universal cost comparison methods. While technically the best solution depends upon the ground conditions and the location of the water table, in practice the financial boundaries of a project and the degree of acceptable financial risk generally play a more significant role in the decision-making process.
The question also arises, 'cost to whom?' The client is responsible for the direct costs of the contract and possibly for any compensation for the loss of amenity or trade by local residents and businesses . This often means that the costs are borne by local citizens and future generations. Furthermore, certain government financial policies can distort the real costs of installing, maintaining and repairing utility services. This can lead to the misconception that open cut is cheaper, when in fact a full accounting of the environmental and social costs may indicate otherwise.
The direct costs of both the trenchless and open cut methods in terms of materials, time and equipment can be established relatively easily. Indirect costs such as reinstatement of the surface, long-term repairs to roads and buildings due to delayed settlement, useful life of the service after work and a degree of risk for unplanned or additional emergency work that may arise during the project can often exceed direct costs. An advantage of trenchless methods is that there are generally less indirect costs because surface access is less disruptive, projects are shorter and hence the social and environmental costs are considerably reduced.
Strategic Considerations
Open cut construction work disrupts roads, buildings and other infrastructure. The duration of these disruptions is a major source of frustration for local residents, business and the general public. This has resulted in growing opposition to construction work in general, including concern for the natural environment, as well as an increase in claims for compensation.
Health and safety of workers, equipment operators and the public is well recognised and has led to the introduction of legislation requiring the use of safe working practices. In the case of underground utilities, the closer workers and operators are to mechanical and electrical equipment, to moving traffic, or the more they have to work in confined spaces the greater the risk of accidents. With trenchless projects, surface excavation is confined to relatively small entry and exit pits or shafts, and it is often possible to locate these away from hazardous areas and road traffic.
In comparison to the use of open cut methods, trenchless projects are characterised by minimal surface disruption over a much shorter period of time.
For a well-managed trenchless project, the public may not be aware that major construction work is actually going on below them.