HS2: Final Breakthrough at Chiltern Tunnel; Fourth Northolt Tunnel TBM Launched

The second tunnel boring machine (TBM) building the HS2 high-speed railway line’s Chiltern Tunnel broke through at the tunnel’s northern portal on 21 March 2024, completing a journey that began in June 2021.TBM “Cecilia” has driven for 16 km underground to join twin sister machine “Florence”. She arrived at the site near the Buckinghamshire town of Wendover on 27 February, after completing her adjacent tunnel drive.

Final breakthrough for HS2’s longest tunnel: On 21 March 2024 TBM Cecilia reached the northern portal of the Chiltern Tunnel
Credit/Quelle: High Speed Two Ltd

Northolt-Tunnel

The HS2 project has hit another milestone at the end of March with the launch of the fourth and final machine for the excavation of the Northolt Tunnel beneath London. The HS2 project has hit another major milestone at the end of March 2024 with the launch of the fourth TBM for the excavation of the Northolt Tunnel
Credit/Quelle: High Speed Two Ltd

The 13.5-km tunnel will run from Victoria Road in Ealing to West Ruislip in Hillingdon. In keeping with tunnelling tradition, the fourth machine is named after a prominent woman – Lady Anne Byron. TBM Anne will bore 5.5 km from Victoria Road in Ealing, near HS2’s Old Oak Common station, to Greenpark Way in Greenford, alongside TBM Emily which launched in February 2024.

The other 8 km of twin-bored tunnels has been under construction since 2022, with TBMs Sushila and Caroline both over halfway through their journey between West Ruislip, on the outskirts of London, and Greenpark Way. The quartet of TBMs are all set to complete their journeys in 2025, when they will be extracted from the ground through giant shafts at Greenpark Way.

HS2’s London tunnels contractor, Skanska Costain STRABAG joint venture (SCS), has delivered an extensive programme of work for the TBM to launch at the Victoria Road Crossover Box, excavating the caterpillar shaped box where eventually the trains will cross tracks on their way in and out of Old Oak Common station.

Anne is the eighth TBM that has been launched to date across the HS2 project between London and the West Midlands to build the five mined tunnels for the
trains:

Euston Tunnel (7.3 km)

Northolt Tunnel (13.5 km)

Chiltern Tunnel (16 km)

Long Itchington Wood Tunnel (1.6 km)

Bromford Tunnel (5.8 km)

In all, almost half of the 105 km worth of twin-bored tunnels needed for the route has now been excavated.

TBM Anne

The TBM was manufactured by Herrenknecht in Germany. It is one of 10 machines specially designed for HS2 and the ground through which they will bore. Two remaining TBMs, which will eventually be used to dig HS2’s final tunnel between Old Oak Common and Euston, in central London, are still being built. TBM Anne was lowered in parts into the 25 m deep crossover box at the end of 2023, where it was reassembled and prepared for launch
Credit/Quelle: High Speed Two Ltd

TBM Anne is an earth pressure balance shield, that weighs 1700 tonnes and is 170 m in length. The cutterhead is 9.11 m in diameter. The TBM was lowered in parts into the 25 m deep crossover box at the end of 2023, where it was reassembled and prepared for launch.

As the machine moves forward, concrete rings are installed to create the tunnel walls. Each ring has an external diameter of 8.78 m, an internal diameter of 8.10 m, and is made up of seven segments. Each segment weighs approximately 7 tonnes. For the Northolt Tunnel East, the concrete tunnel ring segments are being manufactured in Hartlepool by STRABAG.

Euston Tunnel

The two final TBMs will construct the Euston Tunnels, taking HS2 trains into central London. They are set to be delivered to the UK later this year and lowered into the underground station box at Old Oak Common ready for launch.