The third of four tunnel boring machines (TBMs) has completed its 3.4 mile drive beneath the ground at Green Park Way in Greenford, West London, moving HS2 closer to completion of the capital’s Northolt Tunnel.
The TBM, Emily, was first launched in February 2024, and has now completed the excavation of one bore of the tunnel’s eastern section with the removal of 775,000 tonnes of London Clay and the installation of 17,514 tunnel segments.
Northolt Tunnel, which will span a total of 8.4 miles, is being built via the use of four TBMs, with two moving along the western section beginning at West Ruislip and two building the eastern section starting from Victoria Road, North Action.
All four machines are set to finish their journeys at Green Park Way, where each will be lifted out from the underground shaft, with the final TBM expected to complete its journey by 2026.
The twin bore Northolt tunnel will see hS2’s new high-speed trains travel between the outer edge of London and the new Old Oak Common super-hub station in West London, which recently saw the completion of its first platform.
The TBM, which weighs in at 1,700 tonnes and features a 9.11m diameter cutterhead, was given the name Emily after Emily Sophia Taylor, who in 1937 helped establish the Perivale Maternity Hospital before moving on to become Ealing’s first female mayor in 1938. The machine was manufactured by Herrenknecht and was specifically designed to best handle the London Clay it extracted from the earth.
Malcolm Codling, Project Client Director for HS2 Ltd, said:HS2’s tunnelling drives in London for the Northolt Tunnel are nearing completion and it is a real achievement for our team to complete this 3.4-mile section on the tunnel safely and with such efficiency.
There is still much more to do in the tunnel to get it HS2 ready and we will be focusing on productivity to continue with our work safely to get the HS2 route in London ready for track to be laid, and systems installed.
Each of the four machines will finish their drives in a reception can within the shaft due to high water pressure in the ground at the Green Park Way site, allowing for their removal whilst remaining pressure and applying sealant from the tunnel lining itself before depressurisation.
Manned by three teams of 48 workers, the work was carried out by Skanska Costain STRABAG JV (SCS JV), and, during peak times, moved at roughly 38 metres per day, installing concrete segments along the way.
Dave Hannon, Project Director, Tunnels & Routeway, Skanska Costain STRABAG JV said:The arrival of TBM Emily at Green Park Way marks a significant milestone in the programme. We are now approaching completion of the Northolt Tunnel - an exciting achievement and a testament to the collaboration, dedication, and technical capabilities of our teams.
With our continued focus we are pressing ahead at pace to complete the remaining works, including cross passages, tunnel walkways, ventilation shafts, headhouses, and portals, as we deliver on part of the HS2 project.
All London Clay extracted has been taken to the London Logistics Hub at Willesden Euro Terminal before being transported by rail and reused at sites in Cambridgeshire, Kent and Warwickshire.
The three TBMs, Sushila, Caroline and Emily all finished their journeys in December 2024, April 2025 and June 2025, respectively.
The fourth and final Northolt TBM, Anne, is expected to complete its journey this summer.
