TBM Cecilia - HS2 Chiltern Tunnel
Chiltern Hills, UK (South Portal to North Portal) · 2021-2024 (Started May 2021, completed March 2024) · £87.7bn - £102.7bn (HS2 project total, 2025 prices)
The judgement call
Account-gated at launchNamed after Cecilia Payne-Gaposchkin. Completed its 10-mile drive under the Chilterns, joining its twin Florence. Each TBM is a self-contained underground factory, digging the tunnel and lining it with 56,000 concrete segments.
Key engineering challenges
Tunnelling through challenging ground conditions in the Chiltern Hills. - Minimising environmental impact in an Area of Outstanding Natural Beauty. - Managing logistics for a 170m long TBM and its segments.
Project facts
- Client / owner
- HS2 Ltd.
- Lead contractor
- Align JV (Bouygues Travaux Publics, VolkerFitzpatrick, Sir Robert McAlpine)
- Lead designers
- —
- Project type
- new build
- Scale
- TBM length: 170m; Tunnel length: 16.04 km (9.97 miles); Excavated material: 3 million cubic metres (combined with Florence); Drive duration: ~2 years 10 months
- Disciplines
- civil; structural; mechanical; electrical; systems; tunnelling; geotechnical
- Standards & frameworks
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Sources: HS2.org.uk (https://www.hs2.org.uk/building-hs2/tunnels/twin-bore-tunnels/) - TUC Magazine (https://tucmagazine.org/hs2s-florence-and-cecilia-reach-chesham-road/) - Buildindigital.com (https://buildindigital.com/hs2-tunnel-boring-machine-cecilia-completes-her-journey/)