Four TBMs are building the 13.5km tunnel that will carry high-speed trains between HS2’s super-hub station at Old Oak Common, west London, and the outskirts of the capital at West Ruislip.
The machines will excavate 27km of tunnel overall – two bores over the 13.5km length – making it the second longest tunnel on the new railway after one recently excavated beneath the Chiltern Hills.
The first machine, TBM Sushila, was launched eastwards from West Ruislip in October 2022. It was followed one month later by TBM Caroline, which is excavating the adjacent tunnel.
Both will complete 8km of the route, finishing their journeys at the Green Park Way vent shaft in Greenford – just over halfway – where they will be lifted out.
In February this year, TBM Emily began her journey west from HS2’s Victoria Road Crossover Box site near Old Oak Common towards Greenford. She was joined by TBM Anne in May. They will both complete 5.47km of the tunnel.
Combined, the four machines have now travelled over 13.1km – half of the total distance for the twin-bored tunnel. The completion of each tunnel drive will be staggered as they reach the final destination at Green Park Way, with the first TBM, Sushila, arriving later this year.
The TBMs are making an average daily advance of 16m and they have excavated nearly 2 million tonnes of material.
The Northolt Tunnel, which also includes five shafts and headhouses, is being built by the Skanska, Costain and Strabag (SCS) joint venture, which will also construct the Euston Tunnel eastward from Old Oak Common to central London.
“Reaching the halfway point of our tunnelling programme for the Northolt Tunnel demonstrates the huge progress achieved to date on one of the most complex and ambitious programmes embarked upon in the UK. Alongside the tunnelling operations we are now moving into the fit-out stage of the works in readiness for track and rail systems to be installed,” said SCS managing director James Richardson.
“At Old Oak Common, we are gearing up to assemble and install our final two TBMs, ready to take the high-speed line into central London.”
These TBMs are due to arrive in the UK this summer and will be assembled in the underground box at the station site. Timings and funding for the construction of the Euston Tunnel are being confirmed with government.
In May, HS2 revealed that across the route between London and the West Midlands, tunnelling on half of all the twin bored tunnels had been completed.
Two of the tunnels are now complete – the 16km Chiltern Hills tunnel and a 1.6km beneath Long Itchington Wood in Warwickshire. Two others remain under construction – the Northolt Tunnel in London and the 5.6km Bromford Tunnel in the West Midlands taking the line into central Birmingham.
The excavated material from HS2’s tunnels is being reused on several sites. At the West Ruislip portal it is being used around the Copthall Green Tunnel to remodel a nearby golf course that has been impacted by HS2’s tunnelling and to create green spaces in the Hillingdon area surrounding the new railway.
London clay removed from the Victoria Road Crossover Box side of the tunnel is being taken to the London Logistics hub via a spoil conveyor. From there it is taken by rail to reuse sites in Rugby, Kent and Cambridgeshire. The logistics hub has now transported over 2 million tonnes of materials to these sites, which are being used to backfill quarries to support housing developments and wildlife areas for birds.
