The existing 1050mm 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 MDA and Wessex Water to prevent this asset from further deterioration and a potential collapse in the combined sewer was to install a one-piece GRP liner that had an Internal Diameter (ID) of 900mm and a wall thickness of 35mm. The outer diameter (OD) of this pipe at 970mm would still fit inside the existing 1050mm 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 ware 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 250m 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.
The site team worked extremely hard on this scheme to deliver the works to the client’s satisfaction ahead of programme and without a single accident or incident. The site team also received numerous commendations from local residents on how friendly, helpful and efficient they were.