Four tunnel boring machines (TBM) are being used to form the tunnel that will carry high-speed trains between HS2’s station at Old Oak Common in west London and the outskirts of the capital at West Ruislip.
The TBMs are excavating 16.8 miles of tunnel overall – twin bores of 8.4 miles each – making it the second longest tunnel on the HS2 railway after one recently excavated beneath the Chiltern Hills.
The first TBM, named Sushila, was launched eastwards from West Ruislip in October 2022. This was followed one month later by TBM Caroline for the adjacent tunnel.
Both will complete five miles of the route, finishing their journeys at the Green Park Way vent shaft in Greenford – just over half way – 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 the fourth machine, Anne, in May. They will both complete 3.4 miles of the tunnel.
Combined, the four machines have now travelled more than 8.4 miles – 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.
Malcolm Codling, client director for HS2 Ltd, said: “Our London tunnels team are making significant progress taking HS2 from design to reality underneath the capital, building Britain’s new transformational low carbon railway. Completing half of the Northolt tunnel has come after years of work from the team and we are now looking forwards to the TBMs reaching the end of their journeys, with the first arriving at Green Park Way in Greenford later this year.”
Between them, the four TBMs have so far excavated nearly two million tonnes of earth. Spoil removed from the West Ruislip portal is being used to remodel a nearby golf course that has been impacted by HS2’s tunnelling.
London Clay removed from the Victoria Road crossover box side of the tunnel, is being taken to the London Logistics hub using a spoil conveyor. From there it is taken by rail to reuse sites in Rugby, Kent and Cambridgeshire to backfill quarries, support housing developments and build wildlife areas for birds.
The Northolt tunnel is being built by a joint venture of Skanska, Costain and Strabag (SCS JV). The same JV will also construct the Euston tunnel eastward from Old Oak Common to the centre of London, subject to that part of the project actually going ahead.
SCS managing director James Richardson said: “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 fitout stage of the works in readiness for track and rail systems to be installed.
“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.”
Timings and funding for the construction of the Euston tunnel has yet to be decided by government.
Got a story? Email news@theconstructionindex.co.uk
