The Tunnel Boring Machine (TBM) that will excavate the new electricity cable tunnel beneath the River Thames for National Grid’s Grain to Tilbury project has successfully completed Factory Acceptance Testing (FAT) at Herrenknecht AG’s facility in Schwanau, Germany.
This achievement marks a major milestone for the project, which forms part of The Great Grid Upgrade—the largest overhaul of the UK’s electricity transmission network in generations. The new 2.2 km tunnel will replace the ageing 1960s Thames Cable Tunnel between Tilbury and Gravesend, ensuring long‑term resilience for the 400 kV connection that supports the South East’s growing energy needs.
A First for Ferrovial: Mixshield Technology with Slurry System
The TBM represents Ferrovial Construction’s first-ever Mixshield machine equipped with a slurry system, a technology specifically suited to the challenging geological conditions beneath the Thames. Mixshield TBMs are engineered to manage heterogeneous ground, high water pressures, and abrasive materials such as flint — all of which are expected along the tunnel alignment.
According to Herrenknecht, the machine has been designed to withstand water pressures of up to 4.5 bar and to operate effectively in zones of very strong flintstone and high permeability. The successful FAT confirms the TBM’s readiness for these conditions and validates its mechanical, hydraulic, and control systems before deployment.
From Germany to the UK: Preparing for Launch
With testing complete, the TBM is now being dismantled for shipment to the UK. Once delivered to the construction site, the machine will be reassembled within the launch shaft before beginning its 2.2 km drive beneath the Thames.
The tunnel will be constructed by the Ferrovial BEMO Tunnelling joint venture, which is also delivering the project’s major shaft works — including the recently launched Vertical Shaft Sinking Machine (VSM) “Verena,” the largest of its kind ever used in Europe.
Strengthening the UK’s Energy Future
The Grain to Tilbury project is a critical component of National Grid’s long-term strategy to modernise and reinforce the electricity transmission system. Alongside the new tunnel, the programme includes:
• installation of new high‑voltage cables
• construction of headhouses at each end of the tunnel
• reconductoring of overhead lines between Kingsnorth, Grain, and Tilbury
These upgrades will help ensure the network can support increasing volumes of clean, home‑grown energy and meet future demand.
A Significant Step Forward
Completion of the TBM’s FAT marks the transition from design and manufacturing into the delivery phase of tunnelling works. Once operational, the Mixshield TBM will advance beneath the Thames, excavating and lining the new cable tunnel that will serve as a backbone for the region’s energy infrastructure for decades to come. 04/26.
