Further significant progress in excavating the 8.4-mile-long Northolt Tunnel for HS2 was made when the third of four tunnel boring machines completed its work in the tunnel last Friday, 6th June.

Emily made the breakthrough after completing a 3.4-mile drive at Green Park Way in Greenford, west London, and the fourth TBM, Anne, is due to finish its boring this summer.

The second bore was completed by TBM Caroline in April this year.

Emily was named after Emily Sophia Taylor, who helped establish the Perivale Maternity Hospital in 1937 before becoming Ealing’s first female mayor in 1938.

It was launched in February 2024 and worked on one bore of the eastern section of the tunnel, from where it removed 775,000 tonnes of London Clay and installed 17,514 tunnel segments.

Four TBMs are being used to construct the Northolt Tunnel, with two TBMs building the eastern section from Victoria Road in North Acton and two TBMs building the western section from West Ruislip. Each TBM will finish its task at Green Park Way, from where it will be lifted out from its underground shaft.

Because of high water pressure in the ground at the Green Park Way site, the TBMs are finishing their drives in a reception can in the shaft, which allows pressure to be maintained while sealant is applied from the tunnel lining to prevent water ingress.

Emily was designed specifically for the soft London Clay of the tunnel. Built by Herrenknecht in Germany, it weighs 1,700 tonnes and has a 9.11m diameter cutterhead.

Three teams of 48 employed by HS2’s London Tunnels contractor, Skanska Costain STRABAG JV, worked around the clock to bore the tunnel, with Emily advancing at around 38 metres per day at peak production.

Excavated clay was removed from the tunnel on a conveyor system to the London Logistics Hub at Willesden Euro Terminal, then transported by rail and reused at sites in Cambridgeshire, Kent and Warwickshire.

The excavated tunnel shaft was lined with concrete segments, each weighing up to 7 tonnes, and made at Hartlepool in County Durham by STRABAG.

“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.”

Dave Hannon, Project Director, Tunnels & Routeway, Skanska Costain STRABAG JV