HS2 has started excavation of the final tunnel bore on the 140-mile railway between central London and the West Midlands.
The last of 11 tunnelling machines built for the project started its drive from Old Oak Common station in west London towards Euston – the railway’s terminus.
Euston is the second bored tunnel underneath the capital – after the Northolt Tunnel – and is being constructed by HS2’s London tunnels contractor, Skanska Costain Strabag JV.
The tunnel boring machine (TBM) has been launched underground from the Old Oak Common station box, 23m below ground. At its deepest, the Euston Tunnel will be 66m below ground.
The 198m-long machine operates 24 hours a day as an underground factory, excavating the earth and installing concrete segments into rings to create the tunnel.
Overall, on both bores of the tunnel, 48,294 concrete segments will be installed, and 1.5 million tonnes of spoil will be excavated.
Each six-tonne concrete segment has been manufactured by Strabag in a newly-established facility in Hartlepool, before being transported to the capital by rail.
The TBM used for the project is named Karen after Karen Harrison, one of the first female train drivers in the UK, who drove out of Old Oak Common depot.
To mark the milestone, two female train drivers from Avanti West Coast were invited onto the machine to drive it alongside the engineers working on the project.
The latest milestone follows the launch of TBM Madeleine, the first of two machines being used to excavate the twin-bore tunnel. TBM Karen will complete the second bore of the 4.5-mile Euston Tunnel.
Four other tunnels have now been completely bored – the Northolt, Chiltern, Long Itchington Wood and Bromford tunnels.
Prioritising safety and productivity
Jonathan Morris, managing director of Skanska Costain Strabag JV said: “We are proud to launch HS2’s final tunnel boring machine, a major milestone for both SCS JV and the wider project as we excavate the twin-bore tunnel towards Euston.
“During this work, the TBMs will remove over 1.5 million tonnes of excavated material and construct the final section of the tunnels using more than 8,000 precast rings.
“Our teams have already delivered 8.4 miles of tunnels under London and will now continue working around the clock to complete these final drives.
“Achieving this safely and productively is our top priority, with our TBMs progressing at an average rate of around 16m per day while maintaining the highest levels of safety performance.”
The tunnelling operation for the Euston Tunnel is being facilitated by a separate temporary logistics tunnel, which was completed in January 2024.
The 853m Atlas Road Logistics Tunnel will allow the tunnelling team to access both machines, deliver construction materials and remove the excavated spoil.
All the excavated material from the tunnel will be taken via conveyor to the London Logistics Hub at the Willesden Euro Terminal Depot. From there, it is taken by rail for reuse in projects in Kent, Cambridgeshire and Warwickshire.
