The TBM Christine, which is 140-tonne and manufactured by Herrenknecht, has completed its journey in a flooded shaft in south-east London on National Grid’s London Power Tunnels (LPT).
Excavating 2.5km from the launch shaft in Hurst, navigating difficult terrain caused by the chalk aquifer across the route by this machine took four months.
Despite that there was the risk of high-pressure water leakage flowing into the shaft, balancing the water pressure and creating the conditions to allow sealing gel to cure before draining down was successfully done by flooding the shaft by the Hochtief Murphy Joint Venture tunneling team.
Additionally, the TBM was refurbished and modified to operate in these conditions.
The required phases for this breakthrough were three stages, which allowed the team to dismantle the TBM in three parts and the TBM was lifted from the shaft in an eight-day operation.
Indicating to the 26.8km of built tunnel, this is the third drive to be completed on the project, whereas the tunneling is due to be completed with the breakthrough of the two remaining drives (a total of 5.5km) later this year. Four TBMs are working on the project.
According to LPT project manager Malcolm Casewell: “The breakthrough at Crayford was unique on the project. Ensuring Christine was fit for an underwater breakthrough was a great challenge and I’m proud of what we’ve achieved today alongside our engineering partners, HMJV and Herrenknecht.”
As a seven-year project with £1bn value London Power Tunnels is a project to rewire and future-proof London for raising demand through the construction of underground tunnels to house electrical cables that can be easily replaced and supplemented as the city grows.
Location of whole of the constructed 32.5km of 3m-diameter tunnels are up to 60m beneath ground between Wimbledon in south-west London and Crayford in the south-east, which are slated to carry high voltage electricity cables.
The scheduled date for inauguration of the project is 2027.