Bournemouth, Braidley Road, deteriorated sewer restored preventing collapse with Flowtite relining pipes

The existing 1050 mm diameter PCC combined sewer running through Braidley Road in Bournemouth was found to be defective and with the surrounding ground conditions being very fine sand, it was imperative that the asset was structurally repaired before any further deterioration occurred risking a potential collapse leading to a sink hole opening up in the road above.

The solution developed between Matt Durbin Associates and Wessex Water to prevent this asset from further deterioration and a potential collapse in the combined sewer was to install a one-piece Amiblu GRP liner that had an Internal Diameter (ID) of 900 mm and a wall thickness of 35 mm. The outer diameter (OD) of this pipe at 970 mm would still fit inside the existing 1050 mm sewer whilst having sufficient annular space to install a grouted surround.

The existing manhole on the sewer line was modified to be able to get the GRP liners into the sewer, works were carried out during low flow times to ensure the local residents’ facilities were not disturbed. The GRP liners were pushed up to the furthest upstream point of the sewer and then tirfored together working back downstream. This meant the working area could be kept dry by carrying out inline pumping which removed the flows away from the working area.

Upon completion of the 250 m length of GRP liners, circa 80 tonnes of polymer modified grout was pumped into the annulus of the GRP liner over several days to ensure the liner was completed secured and was structurally sound. The works were then inspected prior to sign off and removal of all equipment from the road. The solution has secured the asset for a further 100 years or more.