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Coswarth Project

Barnet projectCoswarth Project


Public Sewer Services (PSS) were approached to urgently replace and upsize a 160mm diameter PVC gravity reservoir drain. The drain was needed to support storage capacity improvements that had been carried out at the existing reservoir that was located in the SW.

The solution

The upstream pipe section had already been replaced, using Horizontal Directional Drilling (HDD) techniques. This method was implemented due to the pipe being located on a busy A road that served as the main access route in and out of the town.

The remaining downstream sections, which spanned 285 metres, were situated across farmland where there was just one gated entry point. This section of pipe needed to be upsized by PSS by five pipe sizes; from a diameter of 160mm to 280mm PE 100 SDR 11.

The ground conditions were assessed by PSS during their initial scoping visit, who confirmed they were perfect for upsizing the pipeline with static hydraulic pipe bursting. Ground heave calculations were also undertaken on the upsizing and deemed acceptable.

Working closely with the client, PSS designed and excavated the launch and reception pits, which incorporated correctly tapered access for the replacement larger diameter pipe. Butt fusion equipment was used to connect the pipe, which was laid next to the existing pipeline.

Cost and productivity benefits

PSS were on site within a week of being contacted by client and completed the work within just six days . PSS used in house plant and equipment and a team their of specialist trained staff, which enabled them to complete the project so efficiently.

The bursting process was one of the quickest installations carried out by PSS to date. The HB100 bursting rig was placed in an intermediate pit in the adjacent field and bursting rods were kept in-situ and reversed up inside the final pipe length. As a result, considerable time and effort was saved by not having to remove individual steel bursting rods. The HB100 bursting rig was then reversed to allow the final pull in and overall completion of the project.
This approach, combined with the experience of PSS’ team, meant the three bursting lengths were completed in just three days, with the three individual lengths all completed in just one hour, each from initial pullback.

Innovative concept

PSS’ trenchless teams worked together to mobilise all of the necessary plant and equipment that were required, which had to be adapted, given the sheer scale of this upsizing project. A four-way lead splitter was fabricated to fit in front of the 340mm tapered expander to facilitate the splitting and upsize in a seamlessly smooth operation.

PSS also invested in numerous static pipe bursting rigs of differing power outputs from around the world. PSS selected their own Hammerhead HB100 bursting rig, which is capable of providing a pullback force of up to 100 tonnes, if required.
The HB100 system, which was positioned in the reception pit, was further adapted to accommodate the requirements – the front excavation face was reinforced with toed in steel sheets and timber to receive the pulling forces generated on a pipeline upsize of this magnitude.

Transport and environmental benefits

Excavating the site as opposed to utilising pipe bursting would have taken months. In comparison, the pipe bursting was carried out in a matter of days, generating substantially less waste, plant, traffic and disruption to local infrastructure.
Overall, this helped reduced carbon emissions by an estimated 90 %

Customer benefits

Thanks to PSS’ expertise and equipment and innovation the client have been provided with upsized asset with increased capacity .What’s more, due to the timely delivery and minimal disruption, the clients reputation has been preserved.

Community benefits

As a result of the work that was carried out by PSS, all of the residents and businesses within the undisclosed town in Cornwall have a continuous supply of drinking water. Furthermore, given the fact the work was carried out so swiftly, the risk of there being a drinking water supply shortage was eradicated before it could become reality.





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