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    Lower Thames Crossing TBM procurement and £11bn cost: tunnelling notes for engineers

    December 3, 2025|

    Reviewed by Joe Ashwell

    Lower Thames Crossing TBM procurement and £11bn cost: tunnelling notes for engineers

    First reported on New Civil Engineer

    30 Second Briefing

    National Highways has started procuring one of the world’s largest tunnel-boring machines for the Lower Thames Crossing, as the project’s forecast cost rises to £11bn for the new road tunnel beneath the Thames Estuary. The TBM will be sized for twin-bore highway tunnels carrying dual carriageway traffic, demanding large-diameter excavation, high face pressures and complex segmental lining logistics in soft estuarine ground. Contractors and designers will need to manage settlement control, water ingress risk and spoil handling at a scale comparable with only a handful of global road tunnel schemes.

    Technical Brief

    • Procurement process has formally started for a mega-diameter TBM dedicated to the Lower Thames Crossing.
    • National Highways is client for the TBM purchase and overall LTC delivery.
    • Supply-chain engagement now needs to address fabrication, shipping and assembly of one of the world’s largest TBMs.

    Our Take

    At £11bn, the Lower Thames Crossing sits at the very top end of UK road infrastructure schemes in our database, signalling that National Highways will be under sustained pressure to demonstrate lifecycle cost savings and congestion relief benefits versus incremental upgrades to existing crossings.

    The use of one of the world's largest TBMs for a UK tunnel project suggests a deliberate move to import mega-TBM experience more commonly seen on Asian and Middle Eastern schemes, which may influence future British tender specifications and contractor prequalification criteria on large-diameter tunnelling.

    Within the 134 Infrastructure stories in our coverage, only a small subset involve UK projects of this capital scale, so LTC is likely to become a reference case for how the UK planning and consenting regime handles very large, long-lead plant procurement decisions under public scrutiny.

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    Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.

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