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Water and waste company Severn Trent has completed a unique flood alleviation scheme in Gloucestershire using innovative underground technology.

The £1.4m scheme in Slimbridge saw the company’s engineers applying ‘flood grout’ to 600 metres of sewer pipes as part of a UK trial of the method.

The FTSE 100 company, along with working partners NMCN, renovated a total of 1.4km of sewer pipes and also installed additional tank sewers, helping to protect the local area from flooding.

Ian Woodward from Severn Trent, who managed the project, said: “Slimbridge is an area which is prone to flooding and we’ve seen problems in the past where ground water has mixed with sewage.“It was the perfect location for the trial and we renovated 1.4km of pipes in three separate phases, with 600m of those being used for the flood grouting trial.”

Flood grouting is a method which uses two different grout materials, which are inserted into the sewers in stages. The grout flows through the damaged sections of pipe, into the surrounding soil particles and then hardens around the sewer pipe when the two grout materials mix together. The technique gives a near-perfect water tightness and seals any defects, while also stopping any groundwater from leaking into the network.

As well as trialling the flood grout technique, the project also involved using other traditional trenchless technologies, including sewer lining, to renew the ageing sewer pipes.

“The initial findings are really positive. Monitoring of both the local sewage pumping station and the ground water levels in Slimbridge is showing that the grouting has been successful in keeping ground water out of the sewers in a really vulnerable area,” adds Ian. 

This is the first time that Severn Trent has used this particular grout technique and following the early findings from the work in Slimbridge, and is a method that the company will consider using in the future, in order to address similar ground water infiltration problems.

The company says it will continue to monitor the effectiveness of the trial over the coming months, during which time the ground water levels will vary.

“With the success of the trial, this means our pipes will see a much longer lifespan,” continues Ian. “So our customers can feel confident they’re protected from sewer flooding for longer.”