London Clay Excavated as Emily Hits Tunnel Breakthrough

A significant achievement has been recorded on London’s HS2 project as tunnel boring machine (TBM) Emily completed its 3.4-mile excavation through the eastern section of the Northolt Tunnel. Launched in February 2024 from Victoria Road in North Acton, TBM Emily broke through at Green Park Way in Greenford on June 6, 2025. The operation removed approximately 775,000 tonnes of London Clay and installed 17,514 concrete segments. This makes Emily the third of four TBMs to finish its section in the 8.4-mile tunnel that will ultimately connect West Ruislip to Old Oak Common station.

Manufactured by Herrenknecht in Germany, TBM Emily is a 1,700-tonne earth pressure balance machine with a cutterhead diameter of 9.11 metres. Its design was tailored to the soft geological profile of London Clay. Crewed by three shifts of 48 personnel, the TBM advanced up to 38 metres daily. Excavated clay was transported via conveyor to the London Logistics Hub, from which it was delivered by rail for reuse at sites in Cambridgeshire, Kent, and Warwickshire. The tunnel lining was reinforced in real-time using precast concrete segments made in Hartlepool.

As the fourth TBM, Anne, nears completion of its route, the Skanska Costain STRABAG JV team is preparing to finalize structural components of the tunnel. These include 34 cross passages, walkways, ventilation shafts, and emergency access features. The tunnel invert is also being constructed to support the future railway track. The completion of Emily’s drive signals strong momentum for the HS2 programme, with full tunnel works expected to wrap up later this year.