Sewer renovation turns to the fold
A project to upgrade 1.4km of sewer main in the picturesque Peak District is using a new kind of folding HDPE pipe developed by Insituform Technologies.
In October last year, Yorkshire-based Insituform Technologies (ITL) started a project to renovate a sewerage pumping main running between two picturesque towns in the Peak District.
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, known as Matlock Bath Phase 3 Pumping Main, is being carried out for client Severn Trent Water (STW). Planning of the works was done by Insituform Blue’s engineers in association with the main contractor for the project – GF Tomlinson Civil Engineering, of Derby, the approved sewerage infrastructure contractor for Severn Trent’s North and West region.
Over the past few years, the pipeline has experienced a number of bursts, and this ongoing situation led Severn Trent to look at options for its renovation. Study of the available options for the 1.4km-long pipeline showed that, due to the heavy traffic on the A6 trunk road beneath which the pumping main runs, an alternative to open-cut replacement would be preferred.
The potential disruption that would have been caused by open-cut with the pipeline running under the main road was also compounded by the fact that the pipe route also passed over the River Derwent at a point adjacent to a visitor attraction, the Heights of Abraham.
The area on the edge of the Peak District National Park is always busy due, in part, to the tourist sights and villages in the area.
It was decided 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 being the PolyFlex system.
In essence, these lining systems comprise a PE pipe that 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 chosen partly because it offered a trenchless solution to the lining project, minimising the potential traffic disruption. Also, it offered a close-fit, relatively thin-walled liner within the host pipe which would ultimately minimise any loss of flow capacity so keeping flow rates to a maximum.
The PolyFlex pressure pipe lining system has been under development by Insituform Blue since early 2006. Designed to answer increasing demand for pressure pipe lining 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, causing the liner to revert towards its original diameter inside the host pipe and achieve a close fit. The PolyFlex product is currently designed to operate in host pipes from 50mm diameter up to 250mm diameter.
The PolyFlex product 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 that 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.
As the name suggests, 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 that 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 up 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.
The total length of the Matlock Bath installation project is 1.4km. Some eight individual installations will be completed during the course of the work.
The sections of lining required to complete the project 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. Up to 1,430m, 450mm-diameter liner will be required for the remainder of the project.
The PE pipe being used to create the liner comprises 450mm-diameter SDR21 PE 100mm- or 295mm-diameter SDR21 PE 100. These are provided as 13.5m-long sticks that are fusion welded on site to form the installation length required.
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