HS2 has achieved a major breakthrough with the completion of the 8.4-mile Northolt Tunnel under London, marking steady progress in Britain’s largest high-speed rail project. This is reported by the railway transport news portal Railway Supply.

HS2 has achieved a major breakthrough with the completion of the 8.4-mile Northolt Tunnel under London, marking steady progress in Britain’s largest high-speed rail project
Image credit: HS2

HS2 tunnel completes 8.4-mile London section

Tunnel Boring Machine Anne finished excavation beneath Greenford after 14 months underground, cutting through London clay and installing the final concrete ring inside a deep underground shaft.

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The Northolt Tunnel stretches from West Ruislip to Old Oak Common and lies up to 35 meters below ground. HS2’s London tunnels contractor, SCS JV, used four TBMs to complete this twin-bore passage.

Two machines excavated from West Ruislip, while Anne and Emily worked from Victoria Road in North Acton. TBM Anne finished the second bore of the eastern 3.4-mile section, completing the entire tunnel.

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At peak, TBM Anne advanced 38 meters per day. Each segment installation weighed up to seven tonnes, with teams of 48 workers operating around the clock in three rotating shifts.

Together, the four machines removed 4.16 million tonnes of clay and installed 14,300 concrete tunnel rings composed of 94,233 precision-built segments manufactured by STRABAG in Hartlepool.

The concrete segments were transported by rail, reducing pressure on London’s roads. The excavated clay was moved to HS2’s Logistics Hub, then shipped across the UK for reuse.

Because of high underground water pressure, the TBMs finished inside sealed steel reception cans. These cans maintained pressure to prevent water ingress and allowed safe removal of the machines.

The tunnel’s width varies — 8.10 meters in the east and 8.80 meters in the west — to meet aerodynamic needs for high-speed travel. Only the Chiltern Tunnel is longer along the HS2 route.

Despite ongoing reviews to control spending, HS2 continues advancing major infrastructure. The next step includes tunnel fitout and cross passage work, with two more TBMs set to launch toward Euston in early 2026.

Richard Adam from SCS JV emphasized that TBM Anne’s safe and timely arrival highlights engineering precision and teamwork. HS2 remains committed to expanding UK rail capacity and creating long-term economic value.

Source: railuk.com

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