Can PE pipe normally be installed by trenchless methods or methods using minimum excavation?
Yes. PE pipe is ideally suited to installation by trenchless or minimum excavation techniques and many of the common methods were initially developed for PE. The techniques used by installers that routinely use PE are:
Pipe Bursting or Pipe Splitting
This technique involves using a device which passes through the existing pipe and breaks it, forcing the fragments into the surrounding soil. The replacement PE pipe is pulled through behind the pipe bursting device. For the replacement of brittle materials such as concrete, cast iron, clay etc, the term pipe bursting is used.
For the replacement of more ductile materials, steel or ductile iron, the device splits the existing pipe and hence the term pipe splitting is used. The techniques allow for replacement with pipe of the same diameter, or the void can be expanded to allow a larger size PE pipe to be inserted.
Several research projects and a great deal of experience has shown that the PE pipe is seldom damaged during pipe bursting or pipe splitting works when these are undertaken following the correct procedures.
Pipe bursting (Borealis)
Directional Drilling or Guided Boring
This technique is ideally suited for crossings under roads, railways, rivers, airport runways, etc. A pilot hole is initially drilled using a steerable drill head and drilling fluid, with an electronic transmitter attached behind the drill head to ensure the correct path is maintained. Further drilling and reaming achieves the required diameter.
The PE pipe can then be assembled at the surface to the required length and pulled into the hole. Equipment is available to measure and record the axial force applied to the pipe during installation to ensure that it is not over-stressed.
If required the annulus between the PE pipe and the surrounding soil can be grouted to provide greater stability if this is necessary, but this must be done in a controlled manner to ensure that the pipe is not overloaded leading to its collapse.
Slip lining is the simplest form of pipeline renovation using PE. The replacement PE pipe is simply pulled through the existing pipe. The length of the section depends on the route of the existing pipe and the location of tees and bends. The replacement PE pipe should be designed to be fully structural and acts as an independent liner. The loose fit of the PE liner pipe in the existing pipe results in a loss of hydraulic capacity.
The void between the existing pipe and the PE liner can be grouted to provide greater stability if this is necessary, but this must be done in a controlled manner to ensure that the pipe is not overloaded leading to its collapse.
Close fit lining
The PE liner is manufactured to a slightly larger diameter than the bore of the existing pipe. The liner is pulled through a tapered die (Swageline) or through tapered rollers (Rolldown) to temporally reduce the diameter and is then inserted into the existing pipe. The liner pipe is then reverted back to its original diameter by pressure or a combination of pressure and temperature to provide a close fit liner, maximising hydraulic capacity.
The PE liner can be designed to be fully structural, acting as an independent liner or can rely on the structure of the existing pipe to act as a dependant liner. The resulting liner is often of a non-standard diameter.
Close fit liners are similar to the above but the diameter of the liner is reduced by folding it into a geometrical shape, typically a ‘C' or ‘U' shape. This reduces its effective circumference and allows for ease of insertion. The liner pipe is then reverted back to its original diameter by pressure or a combination of pressure and temperature to provide a close fit liner.
Folded and reformed liners are better suited to installation in deeper pipes as they can be inserted through existing manholes.
The PE liner can be designed to act as an independent liner or a dependant liner.