Significant HS2 milestone as Chiltern Tunnel complete

Our Align JV are celebrating following the completion of construction for the highly complex Chiltern Tunnel.

The Align team congregate for a picture upon the completion of the Chiltern Tunnel work

The five-year programme involved construction of the 10-mile tunnel, the longest on the HS2 route, the South Portal porous portal structures and accompanying earthworks trace.

Align is our HS2 joint venture with Bouygues Travaux Publics and VolkerFitzpatrick.

Works began in 2020 with the iconic tunnel boring machines (TBMs), Florence and Cecilia, commencing their journeys in spring 2021. Their typical drive is 5-6km, so this circa 16km drive required some technical innovations never used before in the UK.

Since the breakthroughs of the TBMs at the North Portal in early 2024, the team have been finishing the 38 cross passages and 5 adits, the strip out of services and slurry pipes, slipforming the emergency walkways, completing construction of the South Porous Portals and constructing the crossover slabs and drainage for the train track.

The portals are built to eliminate the possibility of ‘sonic boom’ being created by high-speed trains entering at 200mph, a first for the UK rail network.

Through the project's close teamwork and collaboration, the programme was completed 12 days ahead of the contractual date.

An incredibly complex project, it has won multiple awards and showcased some pioneering engineering expertise.

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