A 15m-diameter vertical shaft sinking machine (VSM) has begun excavation work at National Grid’s Tilbury site as part of a project to replace a 1960s cable tunnel under the Thames between Tilbury and Gravesend.

Named Verena, the VSM, designed and built by Herrenknecht, is being used to construct a new 15m internal diameter shaft at Tilbury for the Grain to Tilbury upgrade. The work forms one element of National Grid’s wider Great Grid Upgrade programme, which aims to modernise the UK’s high-voltage transmission network to accommodate more home-grown and renewable power.

Ferrovial Bemo JV (FBJV) holds the £230M contract to construct the 2.2km high-voltage (400 kV) cable tunnel connecting Tilbury and Gravesend. The current Thames Cable Tunnel, installed in the 1960s, has reached the end of its design life, National Grid says, and the replacement is intended to maintain network reliability and facilitate future connections to low‑carbon generation.

The VSM method represents a departure from conventional shaft construction in Britain. The machine operates remotely from the surface and excavates inside a water-filled shaft, with the cutting drum lowering the shaft progressively from the top as excavation proceeds.

NCE recently heard from National Grid and FBJV in detail about the VSM method, which has only been used once previously in the UK – and with a much smaller diameter. In fact, the National Grid shaft is being excavated by the largest VSM seen in Europe.

National Grid and the contractor say the VSM approach removes the need for workers to enter the shaft during excavation and avoids groundwater lowering or treatment, measures that can be necessary with traditional methods. The Tilbury shaft will reach a depth of 48.7m; a second shaft of about 46.3m is planned at Gravesend using the same VSM and method.

Proponents of the technology highlight potential benefits including improved safety, faster progress and reduced environmental impact compared with some established techniques. The water-filled process and remote operation are intended to limit ground movement and manage challenging geology beneath the river floodplain.

The Grain to Tilbury tunnel will carry a new 400 kV cable circuit, part of efforts to strengthen connections across the southeast of England as demand patterns and generation sources change. The Great Grid Upgrade is a long-term National Grid programme to renew ageing assets and expand capacity to accommodate offshore wind, solar and other low‑carbon generation.

Excavation of the tunnel is expected to complete by the end of 2026 but completion of fit out, testing and commissioning will continue into 2029.

The use of a VSM at Tilbury is among a growing number of projects exploring mechanised shaft sinking in the UK, reflecting an industry shift toward methods that can reduce on-site risks and emissions.

The VSM shaft excavation method has safety, efficiency and carbon benefits

National Grid project director Mark Farmer said: “The Grain to Tilbury project is helping to future-proof the UK’s electricity network.

“The launch of the Vertical Shaft Sinking Machine marks a major milestone for the project. Through collaboration and innovation, this technology is helping to deliver resilient infrastructure under the Thames, securing reliable electricity for the decades ahead.”

Ferrovial Bemo JV project director Borja Trashorras said: “Launching Europe’s largest diameter Vertical Shaft Sinking Machine at Tilbury is a milestone achievement for our team and for UK infrastructure. This technology allows us to deliver the Grain to Tilbury project with enhanced safety, efficiency, and environmental performance.

“We’re proud to be working in partnership with National Grid and Herrenknecht to bring this pioneering solution to life, helping to future-proof the electricity network for generations to come.”

Herrenknecht board of management member Ulrich Schaffhauser said: “We’re honoured to be a trusted partner of Ferrovial Bemo JV and National Grid in this milestone project.

“Delivering Herrenknecht’s largest-ever VSM for the shafts, and the Mixshield TBM for the cable tunnel, supported by essential equipment and dedicated service, we proudly contribute to the project’s successful completion.”

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