Construction work on HS2’s longest tunnel (the Chiltern Tunnel), measuring 16 km in length, has been completed, representing a major civil engineering milestone for the new high-speed railway.
The completion of the civil engineering works will be followed by the installation of mechanical, electrical, and plumbing equipment, with the design phase already underway and preparatory work set to begin this year. The railway systems, including the tracks and overhead electrical equipment to power the new high-speed trains, will be installed after these works are completed.
Once equipped with rails and the electrical system, as part of the later phases of the project, the tunnel will allow trains to travel at 320 km/h, covering the 16 km in just three minutes.
The Chiltern Tunnel was built by Align JV, a partnership between Bouygues Travaux Publics, Sir Robert McAlpine, and Volker Fitzpatrick.
The tunnel boring machines (TBMs) advanced northwards at an average speed of 16 meters per day, emerging near Great Missenden, Buckinghamshire, in early 2024. Since then, work has continued on the construction of the north and south portal extensions, the installation of internal walkways, and the construction of 40 cross passages.
The drilling machines operated non-stop, and each of the two TBMs received a constant supply of 56,000 tunnel lining segments, weighing 8 tons each, produced in a specially built factory near the southern portal of the tunnel. The TBMs excavated three million tons of chalk during the 33 months of work (6.5 years, during which other excavation work was also carried out as part of the Chiltern Tunnel).
This is the second of HS2’s five twin-bore tunnels to be structurally complete, following the same milestone for the 1.6 km Long Itchington Wood tunnel in Warwickshire last year.
Main construction for HS2’s longest twin-tube tunnel – each for a single track for northbound and southbound trains – began in May 2021 with the phased launch of two 2,000-tonne tunnel boring machines (TBMs) from a site near the M25 motorway, near Maple Cross, Hertfordshire.
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