Articles & Case Studies


Posted: Friday 6th March 2009

Lincolnshirecivil engineering firm UCS Civils recently completed a technically challenging localised pipe repair to a concrete sewer using no-dig trenchless technology. At 1200mm in diameter this was the largest ever local liner repair successfully completed in theUKto date.

When Anglian Water received a call from the Highways Authority informing them of a hole which had appeared in St Thomas’ Road in Spalding, Lincolnshire, Civil Asset Engineer Mick White quickly called in UCS Civils’ Emergency Crew.

By the time they arrived on site shortly after the phone call, the hole revealed a three to four metre cube void under the road surface and according to UCS Civils’ Site Manager Andrew Bellamy it quickly became clear the problem was more serious than they initially thought.

“We got called out to a suspected sewer pipe collapse but following further excavations we realised the midriff of the concrete pipe, from the half-barrel upwards, had been eaten away by hydrogen sulphide gas emitted by the sewage.

Mick White commented, “As it was one of the main sewers in Spalding, to install a new pipe would have meant tankering at up to 36 pumping stations, which would have affected three-quarters of the homes and businesses in the town and cost a colossal amount of money. The pipe also carried some surface water and in the event of any heavy rainfall the flows would have increased immensely.”

To overcome these problems UCS Civils and Anglian Water jointly decided the best option would be to employ a patch repair technique normally reserved for much smaller pipes to prevent any further collapses. Due to the problems of constant high flows it was necessary to install over-pumping into the nearby pumping station while the patch repair was carried out.

Although the pipe had been eroded to an enlarged 1350mm in diameter by the effect of the hydrogen sulphide the largest inflatable packer available was only 1200mm across. According to John Kelly, the MD of CJ Kelly Associates Ltd who are the UK consultants for MC Building Chemicals who manufacture the trenchless technology system, there was some scepticism as to whether the technique would actually work.

“This patch repair system is widely used in the UK but had not been tried on pipes of this diameter before, and because the packer was smaller than the pipe we weren’t sure how effective it would be.

“However, by using this method UCS Civils managed to avoid having to excavate and replace a vital piece of pipe in the Spalding sewerage system which would have been a lengthy and costly undertaking.”

The patch repair technique involved mixing together an epoxy resin with a hardener which was pasted onto the patch. The inflatable pipe packer was covered with a polythene tube to prevent the patch from sticking to it. The patch lining was then rolled around the packer and positioned in place in the sewer. The packer was filled with air to press the patch against the existing sewer wall and left for two to three hours while the resin cured. The packer was deflated and removed, leaving the fibreglass patch lining in place which the team then inspected using CCTV to verify its integrity.

All the packers had to be lined up from the wet well to the excavation site. Initially Anglian Water considered creating a manhole but decided this wasn’t possible because of the cost and safety implications. Instead UCS Civils formed by a new pipe by double-lining what was left of the existing main with the fibreglass patch, laying a reinforced concrete slab over the top and backfilling it to highway specifications.

Using the patch repair system, distributed exclusively by the Sewer Centre in the UK and Ireland, UCS Civils managed to line approximately 15 metres of pipe work in a densely populated residential area without having to dig any trenches. The only place the crew had to dig was where the pipe had collapsed, which meant there was far less disruption than there would otherwise have been. They also managed to avoid creating any new manholes and considerably extended the lifespan of the existing pipe, which saved Anglian Water thousands of pounds.

Commenting on the success of the project, Site Manager Andrew Bellamy said: “Prior to this we had done a number of patch repair jobs for Anglian Water using this technique, although admittedly not on a pipe of this size.

“Following the success of this job we hope to be able to apply the technique to similar sized sewer repairs in the future and continue to save our customers valuable time and money.”

Anglian Water’s Civil Asset Engineer Mick White added: “The collapsed pipe was adjacent to a manhole which had a total of 36 pumping stations flowing into it so the flow was very high and constant.

“The alternative to packing the pipe was to switch the incoming pumping stations off but as time was of the essence and a number of the stations were either located in people’s back gardens or where tanker access proved extremely difficult, so this wasn’t a viable option.

“It was also unfortunate timing as the work was happening at the same time as the world famous Spalding Flower Parade. However the job took a lot less time than initially feared and we only had to close one road which caused very little disruption to the parade and other road users.

“This was an innovative solution as not only was it the largest patch repair in the UK to date, but also the patch lining formed a new section of the pipe. As far as we can tell it’s been a very successful repair and if circumstances allow we will definitely consider using this kind of technique again in the future.”

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