The construction of HS2’s Northolt Tunnel has reached a significant milestone, with 50% of the dig now complete.
The 8.4-mile twin-bore tunnel, which passes underneath London, is now half-dug, as four tunnel boring machines (TBMs) continue to excavate a total of 16.8 miles.
The first machine, named Sushila, was launched eastwards from West Ruislip in October 2022. One month later TBM Caroline began her parallel dig. Both TBMs will complete five miles before finishing their digs at the Green Park Way vent shaft in Greenford.
Meanwhile, in February this year TBM Emily began her dig from the opposite end of the tunnel’s proposed route, at HS2’s Victoria Road Crossover Box site near Old Oak Common. She was joined in May by the fourth and final TBM, Anne. These two TBMs will complete 3.4 miles of the tunnel.
Between them, the four machines have now travelled over 8.4 miles, equivalent to one of the two tunnels that needs to be dug. This amounts to almost two million tonnes of earth which have already been excavated.
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.”
All four machines are progressing at a rate of 16 metres a day, with TBM Sushila expected to be the first to complete her dig later this year. As the TBMs progress, other vital features including cross passages, vent shafts and headhouses are also put in place.
The completed tunnel will carry HS2 services between super-hub station Old Oak Common and the outskirts of London at West Ruislip.
It is the second-longest tunnel on the new railway after the 10 mile-long twin-bore Chiltern Tunnel.
The Northolt Tunnel is being built by a joint venture comprising Skanska, Costain and STRABAG. The same JV will also construct the Euston Tunnel eastward from Old Oak Common to the centre of London. Two further TBMs are expected to arrive in the UK this summer to begin the dig.
Image and video credit: HS2
