A 2.2km high-voltage electricity cable tunnel being built underneath the Thames has reached the halfway point ahead of its planned opening in 2029.
The £230m project is a new high-voltage electricity link that will replace the existing 1960s Thames Cable Tunnel. It forms part of The Great Grid Upgrade, the largest overhaul of the electricity grid in generations.
A tunnel boring machine (TBM) known as Caroline has been deployed to create the new infrastructure, and it has passed 1.1km beneath the River Thames since it first broke ground in May 2026. So far, more than 40,000 tonnes of material have been excavated and over 5,100 pre-cast concrete tunnel segments installed to form the tunnel lining. Just over 840 rings have been installed, and the tunnelling team has achieved its best daily performance of 29 tunnel rings installed within a 24-hour period.
Weighing 464 tonnes, the TBM, together with the trailing gear, is excavating the tunnel using a specialist Mixshield system. Named after...