HS2 Chiltern Tunnel completion marks 16 km milestone

Work has been completed on the HS2 Chiltern Tunnel completion, the project’s longest tunnel, marking a major civil engineering step for the new high-speed railway. The 16 km twin-bore structure is now finished in terms of its main construction.

This is reported by the railway transport news portal Railway Supply.

Next steps after Chiltern Tunnel HS2 construction completed

With the civil phase wrapped up, the focus turns to fit-out. Mechanical, electrical and plumbing (MEP) equipment is next, with design already underway and preparatory work set to begin this year. Once that is done, HS2 will move on to the railway systems, including track and overhead electrical equipment to power the future high-speed trains.

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In later phases, when rails and the electrical system are installed, trains will be able to run through the 16 km tunnel at up to 320 km/h, covering the distance in around three minutes.

Align JV and the tunnel boring machines (TBMs)

The Chiltern Tunnel was built by Align JV, a partnership between Bouygues Travaux Publics, Sir Robert McAlpine and Volker Fitzpatrick. Two tunnel boring machines (TBMs) advanced northwards at an average rate of 16 metres per day, emerging near Great Missenden, Buckinghamshire, in early 2024.

Since that breakthrough, work has continued on the north and south portal extensions, the installation of internal walkways, and the construction of 40 cross passages.

Tunnel lining segments, chalk excavation and HS2 twin-bore tunnels

The drilling operation ran continuously and relied on a steady supply of precast lining. Each TBM received 56,000 tunnel lining segments, weighing 8 tonnes each, produced at a specially built factory near the tunnel’s southern portal.

Across the programme, the TBMs excavated around three million tonnes of chalk during 33 months of work (within a 6.5-year period during which other excavation work was also carried out as part of the Chiltern Tunnel).

The Chiltern Tunnel is the second of HS2’s five twin-bore tunnels to become structurally complete, following the same milestone for the 1.6 km Long Itchington Wood tunnel in Warwickshire last year.

Main construction on HS2’s longest twin-tube tunnel began in May 2021, with the phased launch of two 2,000-tonne TBMs from a site near the M25 motorway at Maple Cross, Hertfordshire, creating separate bores for northbound and southbound single-track running.

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