The first contracts for two new giant tunnel boring machines have been signed to dig HS2 tunnels under North-West London.
The tunnel boring machines (TBMs) are being built in Germany by Herrenknecht, who also built the Crossrail TBMs, and will be delivered to the site in the UK by the end of 2021. They are being designed and manufactured specifically for the London clay and chalk ground conditions they will bore through.
The HS2 tunnels, at 13 miles in length are coincidentally the same length as the Crossrail tunnels – but with a diameter of 8.8 metres, they are much larger than Crossrail’s 6.2 metre diameter tunnels.
Once the first new TBMs have been built, they will be transported by sea before being delivered to the site at the end of 2021. Once assembled, they will begin the tunnel drive from mid 2022, until completion at the beginning of 2024.
The London tunnels will begin just outside of Euston station and will be below ground until they emerge in West London at Old Oak Common station. The route will continue underground from Old Oak Common to the outskirts of West London.
These first two London TBMs will be launched from a portal at West Ruislip and will travel 5 miles east, creating the western section of the Northolt Tunnel. Once they arrive in Greenford the machines will be extracted from the ground and the site will then be used as a vent shaft. The 8.4 mile tunnel will be completed with a 3.4 mile tunnel drive from Old Oak Common using two further TBMs which are yet to be ordered.
A second tunnel between Euston and Old Oak Common will complete the remaining 4.5 miles of London tunnel between the two HS2 stations.
Overall there will be 10 TBMs purchased to construct the 64 miles of tunnelling along the HS2 route between the West Midlands and London.