The River Humber Feeder 9 pipeline is of national importance, connecting an import location for gas and supporting the delivery of gas supplies to millions of customers throughout the UK.
Underwater surveys highlighted an unprecedented amount of erosion near Feeder 9 which had exposed sections of the pipeline. As a long-term solution this project was required to replace the existing pipeline with a new 1,050 mm high pressure gas pipeline under the estuary of the River Humber, inside a precast concrete lined tunnel.
Despite the huge technical challenges involved, our project team, in collaboration with National Grid, developed a solid technical solution for the installation of circa 5 km pipeline into a flooded tunnel.
The tunnel between the launch pit in Goxhill and the reception pit in Paull has an overall length of 4,862 m. Beneath the estuary the tunnel drive is virtually horizontal and will revert to an inclined gradient of approximately 4% on the north bank of the estuary for the last 600 m. Regarding ground conditions, excavation is mainly within the Burnham and Flamborough with a minimal overburden to the seabed of approximately 10 m. However, within the launch pit and reception shaft the tunnel passes through layers of the Alluvium and Glacial Deposits.
Following completion of the tunnelling, drive and strip out of the tunnelling services was undertaken to prepare for the pipeline insertion. No pipe welding activities were possible within the tunnel and therefore the pipes (each 12 m long) were welded into strings of between 612 m and 624 m within our work site near the launch shaft allowing tunnelling activities to continue simultaneously. A total of 13 winches or strand jacks were used to move the pipe strings laterally, on bogies, across the foundations in the yard.