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Getting to the heart of sewer repair

Wessex Water's award-winning Re-Rounder, inspired by heart surgery techniques, helps get deformed sewer networks back into shape. Jamie Hailstone reports.

They say inspiration can come from anywhere but, in the case of Wessex Water’s multi-awarding sewer repair robot, it came from human heart surgery.

The Re-Rounder device, which recently won a hat trick of awards from the United Kingdom Society for Trenchless Technology (UKSTT), has been designed and built to bring 150-millimetre diameter sewer pipes, which have suffered up to 25 per cent deformation, back to their original shape prior to CIPP lining.

The robot picked up the UKSTT’s Innovative Product and Renovation Water and Wastewater Sector prizes, along with the overall Project of the Year award.

It comprises a robot that ‘re-rounds’ the pipe by leaving in place a metal stent, much like the ones now used by heart surgeons.

The stents are made from stainless steel and are laser cut to allow expansion of the stent, without the need for a traditional “metal-on-metal” rachet system used by the pneumatic systems on the market.

The designs of the stents were borrowed from cardiovascular surgery and are 1.2-millimetres in thickness.

“We wanted an efficient and structurally sound design, with the lowest thickness, and without any ratchets which would be an impediment to flow,” Wessex Water’s sewer rehabilitation programme manager, Julian Britton, says. “We also wished to avoid cross-sectional area loss.”

The stents are purposely manufactured with a shallow ‘V’ in the full metal axial sections to ‘bite’ into the host pipe.

This is to ensure the stent does not move when workers jet clean the sewer repair prior to lining.

The machine can be used with rigid clay or concrete sewer pipes, as well as pitch fibre pipes.

Wessex Water owns almost 20,000 kilometres of 150-millimetre diameter wide sewers. Pitch fibre pipes are also known to contain asbestos, which can raise additional problems in terms of excavating.

“We completed proof of concept, and then undertook a worldwide patent search to establish its uniqueness and innovation,” Britton adds. “We could not find any comparable device and complete package delivery system, with a patent in place.”

The robot was trialled on numerous sites in 2018 before being deployed in March 2019 on a sewer regeneration project in Malmesbury, Wiltshire, where it helped avoid an all-day dig and achieved an 85 per cent cost saving.

The utility firm was mobilised to renovate a 52-metre long stretch of sewer, which was 150mm in diameter, with numerous defects.

The sewer was routed along Abbey Row, which is a one-way street due to its narrow width. The road is a main artery and the necessary road closure meant a five kilometre detour. 

According to Wessex Water, the highways authority Wiltshire County Council was reluctant to allow a road closure due to disruption it might cause.

It was even more so when informed that the sewer length had four locations where there was up to 21 per cent deformation, and as this degree of deformation could severely reduce the long-term capabilities of the polyester lining proposed.

In addition, the manhole downstream was off-highway. In the weeks before lining, Wessex Water surveyed the sewer and measured it continuously with its in-house laser to ensure the robotics with a maximum diameter of 116-millimetres over the wheels could be deployed under the defects.

The Re-Rounder robot was used to avoid the four excavation points, and works were restricted to a 48-hour window over the weekend.

Works commenced with a sewer cleaning and the stents were installed within three hours.

Wessex Water estimates that if it had excavated down into the sewers, it would have needed four gangs, all working long hours on the Saturday, down to the two metre depth and reinstatement.

It also says the cost savings of using the robot were considerable. Generally, the excavations between two and three metres deep would have cost between £5,000 and £7,000 each, whereas the robot interventions were a fraction of that.

Regarding the design of the liner in Malmesbury, it was designed against American ASTM F1216 for a ‘fully deteriorated’ structural lining for the deepest section of the sewer at three metres.

Instead, the company’s long-term framework contractor Onsite Central Ltd, installed a three per cent undersized lining, and post lining. By all accounts, it was not readily evident to the eye where the stents had been placed without knowing the meterage.

Over the weekend, many passing residents stopped and enquired as to the device being used. Wessex Water had personnel on site specifically to answer questions and promote the benefits of all the trenchless technology being used on the day.

“Customers and residents like to express their appreciation that utilities such as ours are constantly searching to mitigate the impact of our necessary repair interventions upon their day-to-day activities,” Britton says.

“We’re firmly of the mind that with these new tools, most of the ‘keyhole surgery’, to continue the cardiovascular theme, are now available to clients such as us, to avoid excavation.

“We do not claim any credit for the expansion concepts which we have copied from heart surgery for the stent but believe it is ideal in overcoming unnecessary loss of cross-sectional area, on small diameter sewers, which can least afford the loss of hydraulic capacity.

“The next size of robotics will be a joint 225/300mm, which is currently under design. With greater diameters come greater depth of cover and, had a 300mm diameter machine been available to us some five years ago, a collapsing sewer in running sand in Poole, which cost some £250,000, chasing the defect over 15 metres, could have been saved for just a few thousand pounds.

“The Re-Rounder brings us a more holistic ability to repair collapsing sewers and it’s great that other people in the industry see the benefits of this technology. Going forward, my team and I are excited to be able to further reduce the company’s need to excavate repairs.”

Topic: Sewer Networks
Tags: wastewater , sewer rehabilitation , sewers , Pipes , Wessex Water


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