National Grid completes Thames electricity tunnel ahead of schedule

National Grid has completed the tunnelling phase of its Grain to Tilbury electricity infrastructure project ahead of schedule. The 4.73m-diameter tunnel boring machine, named Caroline, successfully completed its 2.2km drive between Tilbury in Essex and Gravesend in Kent on 27 September.

The project, which aims to install a new high-voltage electricity cable tunnel, finished its excavation 49 days earlier than planned. The drive was managed by the Ferrovial BEMO JV in partnership with Mott MacDonald. To maintain hydrostatic pressure during the breakthrough into the Gravesend reception shaft, the process was conducted under flooded conditions to prevent groundwater ingress.

Following the breakthrough, the machine will move to its final position to complete the remaining tunnel lining works. Dewatering of the reception shaft is expected to continue through October, after which the TBM will be dismantled.