Folding pipe fixes sewage main
A sewer renovation project in the picturesque Peak District is using a new type of HDPE pipe, which folds into a U-shaped profile to reduce its diameter, writes Ian Clarke on behalf of Insituform Technologies
The towns, Matlock and Matlock Bath, lie on the edge of the Peak District National Park, surrounded by Stoke-On-Trent, Sheffield and Derby. The project is known as Matlock Bath Phase 3 Pumping Main and is being carried for client Severn Trent Water.
Planning of the works was undertaken by engineers from the Insituform Blue division of Insituform, in association with the main contractor for the project GF Tomlinson Civil Engineering, the approved sewerage infrastructure contractor for Severn Trent's North and West region. The pipeline route runs between Matlock, laying to the north, and Matlock Bath. Over the past few years, the 1.4km-long pipeline has burst a number of times. This led Severn Trent to look at options for its renovation. And, due to the heavy traffic on the A6 trunk road above the mains, an alternative to open-cut was preferred.
The potential disruption that would have been caused by open cut with the pipeline running under the main road was also compounded. This is because the pipe route passed over the River Derwent at a point adjacent to a visitor attraction called the Heights of Abraham. And the area, on the edge of the Peak District National Park, is usually busy with tourists.
It was decided that the work would best be completed using the new PolyFold lining system from Insituform Blue, which was appointed as the approved lining subcontractor for the project. PolyFold is one of two high-density polyethylene (HDPE) pressure pipe systems offered by the company. The other is the PolyFlex system. In essence, these lining systems comprise a PE pipe, which is deformed to fit easily inside the host pipe being renovated. The liner is then reverted back to its original round shape to form the required close fit lining. The PolyFold system was a trenchless solution to the lining project, minimising the potential traffic disruption, and also offered a close fit, relatively thin-walled liner within the host pipe. This would ultimately minimise any loss of flow capacity so keeping flow rates to a maximum.
The PolyFlex pressure pipelining system has been under development by Insituform Blue since early 2006. Designed to answer increasing demand for pressure pipelining systems in the water supply industry, the system drives circular PE pipe through specially designed rollers.
A winch is also used to aid the passage of the liner through the host pipe. The rollers reduce the liner pipe diameter, allowing it to pass into the host pipe being lined.
Once fully installed in the host pipe, the liner ends are expanded out and fitted with end connections. Next, the liner is filled with water and pressurised, which causes the liner to revert towards its original diameter inside the host pipe and achieve a close fit.
PolyFlex is currently designed to operate in host pipes from 50mm to 250mm diameter. It can be designed to form either a fully structural lining using thicker wall, lower SDR value PE pipe or a semi-structural/interactive liner using a higher SDR value PE pipe. The latter relies on the host pipe having residual strength, which the liner uses to fully withstand internal pressures once in operation.
In parallel to this development, Insituform Blue developed the PolyFold lining system, which is to be used on the Matlock project. This system is appropriate for work in larger-diameter pipes over longer distances.
This system forms PE liner pipe by folding it into a U-shaped profile to reduce its effective diameter for easy installation into the host pipe. To do this, the pipe passes through a specially designed folding rig. On this rig, a hydraulic pushing machine advances the liner pipe through guide rollers and pipe-folding wheels.
The end of the liner is attached to a winch at the reception pit, which guides it through the host pipe during installation process. To ensure that the liner does not revert in the host pipe until required, the folded pipe is strapped as it exits the folding rig. This strapping holds the folded liner in its reduced-diameter profile until the lining pull-in is completed.
Once the pull-in is complete, the liner ends are opened out using air bags and end connections are fitted. The liner is then filled with water and pressurised to burst the banding and re-round the liner, again achieving a close fit lining of the host pipe. The PolyFold system can be used on pipe diameters from 300mm to 1,200mm.
Both systems use a lubricating bentonite slurry, which is painted on the outside of the liner as it passes into the host pipe in the launch pit. This slurry reduces the installation tonnages required to pull or push the liner through the host pipe, a significant requirement with longer lining lengths. The PolyFold system also has the ability to operate as a butt-and-pull process, where shorter lengths of pipe are joined together during installation to make up the final lining length, thereby reducing the overall site footprint.
Eight individual installations will be completed during the course of the work to make up the 1.4km installation project. The sections of lining required will comprise either a 300mm- or 450mm-diameter installation.
On the section of pipe from the start of the project up to a length of 107m, a 300mm diameter will be used. For the remainder, up to 430m- 450mm-diameter liner will be required.
The PE pipe being used to create the liner comprises 450mm-diameter SDR21 PE 100 or 295mm-diameter SDR21 PE 100. These are provided as 13.5m-long sticks, which are fusion-welded on site to form the installation length required. John Beech, business, development manager for Insituform Blue says: "Despite working on a very busy main road with restricted highway space being available, Insituform Blue and Tomlinson have demonstrated their ability to overcome these difficulties and produce a quality solution for the client."