Herrenknecht has been selected to design and build the record-breaking TBM that will excavate the twin bores of the Lower Thames Crossing, marking another major milestone for the UK’s largest road tunnel project.
The German manufacturer will build what is set to become the largest TBM ever used in Europe and the largest machine ever constructed at Herrenknecht’s Schwanau headquarters. The 16.4m diameter Variable Density TBM will also feature the company’s largest accessible cutterhead and is expected to incorporate several industry-first innovations.
The machine has been procured by the Bouygues Travaux Publics Murphy Joint Venture (Bouygues TP Murphy JV), which is delivering the Lower Thames Crossing tunnels and approaches.
The 120m-long, more than 5,000-tonne TBM will be delivered to the UK in sections by sea before being transported via the River Thames to the Port of Tilbury where it will begin tunnelling in 2028.
The single TBM will excavate both 4.2km tunnel drives. After completing the first bore beneath the Thames, the machine will be turned around underground in a planned U-turn operation before excavating the second tunnel. The approach is intended to reduce both project costs and embodied carbon.
The Variable Density TBM has been designed to cope with the challenging geology beneath the Thames Estuary, passing through water-bearing ground, London Clay and chalk at depths of up to 60m. The electrically powered machine will operate using renewable energy.
Frédéric Battistoni, Head of Project Management at Herrenknecht, said: “The Lower Thames Crossing TBM will be the largest machine ever built at Herrenknecht’s headquarters in Germany and the largest Variable Density TBM ever. It will also be equipped with the largest accessible cutting wheel ever built by Herrenknecht.
“Incorporating several industry-first innovations, the machine has been designed to adapt to changing ground conditions while enhancing safety, efficiency and logistics during tunnelling operations. The machine will support the excavation of both tunnel drives through a planned U-turn configuration.”
Didier Jacques, Tunnel Construction Director at Bouygues Travaux Publics Murphy Joint Venture, said the team would now work closely with Herrenknecht on the detailed design of the machine while continuing to focus on reducing carbon emissions, improving safety and delivering innovative construction solutions.
The Lower Thames Crossing will provide a new road crossing east of Dartford to relieve chronic congestion on the existing Dartford Crossing and improve freight links between the ports of south-east England, the Midlands and northern England.
National Highways said the project remains on schedule, with tunnelling due to commence in 2028 following the start of construction earlier this year. The new crossing is expected to open in the early to mid-2030s.
The twin three-lane tunnels will be more than twice the size of the existing Dartford tunnels and form part of the 23km Lower Thames Crossing route. Around 80% of the route will be contained within tunnels, cuttings or landscaped embankments to minimise its visual and environmental impact.
The project, which received Development Consent in March 2025, also aims to become the UK’s first major infrastructure scheme to achieve carbon-neutral construction through measures including low-carbon concrete tunnel linings, design optimisation and renewable-powered construction equipment.
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