Barhale to install concrete lining in London water main as protection from HS2 tunnelling works

Barhale has been awarded a contract by Thames Water to reinforce a 70m long section of the Thames Lee Tunnel running across the route of HS2 in Camden, North London. The value of the contract has not been disclosed.

The 31km Thames Lee Tunnel was built between 1955 and 1959 to carry water from the River Thames at Hampton Water Works to Lockwood Pumping Station at the Lee Valley Reservoir Chain. Its depth varies from 21m to 58m and it was designed to transfer 550ML of water per day.

Barhale will reinforce a 70m long section of the 2.7m diameter concrete-lined tunnel water main to protect it from future HS2 tunnelling works beneath it. When these tunnelling works will take place remains uncertain, as in April HS2 Ltd announced that works on the 7km Euston Tunnel have been paused.

The structural mitigation works will take the form of a reinforced concrete secondary lining. The tunnel will be relined with poured concrete, with steel fixing done ahead of the concrete work. Shutters will be installed in situ by the team, with concrete poured and cast in place.

The outline design solution consists of a 72m long, 220mm thick liner, with a nominal internal diameter of 2240mm. The outline reinforcement details 16mm diameter circumferential bars installed 125mm apart and 8mm diameter longitudinal steel bars installed every 250mm along the internal face of the tunnel.

The location of this section of the water main makes the work more challenging, as it will necessitate an unusually long concrete pump.

The site of the relining is 800m away from the closest access shaft, the Barrow Hill shaft at Primrose Hill. Barhale's Water Director Southern Region Shane Gorman said that the levels of service and utility congestion in the area means that boreholes cannot be sunk to facilitate the process.

Barhale has been working with Camfaud to design a bespoke concrete pumping solution that will work over more than 800m distance.

Commenting on the project Gorman said: "We have worked closely with Thames Water on the design and scheduling of this project. Such is the strategic importance of the Thames Lee Tunnel that outages can only be scheduled for certain times of the year and they are contingent upon general storage levels across the rest of the network.

"We have now identified a suitable window and look forward to successful completion in February 2024."

Barhale will commence works on site in August.

This week, the civil engineering contractor will start works to reinforce another Thames Water tunnel running under the HS2 route.

Barhale will install a protective liner along a 75m length of the Middle Level Two sewer in North London, which is part of the Victorian sewer system created by Joseph Bazalgette.

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