Halfway there: HS2’s Northolt Tunnel reaches 8.4 miles under west London
The four railway tunnels that make up HS2’s Northolt Tunnel under west London have reached the halfway mark, with the four tunnel boring machines completing 8.4 miles of tunnels.
The tunnel links the HS2 station at Old Oak Common to West Ruislip, where the railway then comes back above ground to pass over the Colne Valley before diving back into tunnels next to the M25 motorway.
The tunnel boring machines (TBMs) will excavate 16.8 miles of tunnel overall – two tunnels next to each other, each 8.4-miles long – making it the second longest tunnel on the new railway after one recently excavated beneath the Chiltern Hills.
The first TBM, named Sushila after a local teacher, was launched eastwards from West Ruislip in October 2022. This was followed one month later by TBM Caroline, named after astronomer Caroline Herschel, which is used to excavate the adjacent tunnel.
Both will complete 5 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, which is named after Emily Sophia Taylor, began its journey west from HS2’s Victoria Road Crossover Box site near Old Oak Common towards Greenford. She was joined by the fourth machine, named Anne, after Lady Anne Byron, in May. They will both complete 3.4 miles of the tunnel.
Combined, the four machines have now travelled over 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 their final destination at Greenford, with the first TBM, Sushila, arriving later this year.
Each machine operates like an underground factory, excavating the tunnels, lining them with pre-cast concrete tunnel segments, grouting them into place before moving forward at an average speed of 16 metres per day. Teams work around the clock below ground on the TBMs along with teams on the surface supporting them.
Marking the significance of the tunnelling milestone, Malcolm Codling, Client Director for HS2, 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. ”
As the TBMs progress, other vital features of the tunnel are put in place such as cross passages, vent shafts and headhouses. Along the Northolt Tunnel there are five shafts and headhouses which will provide ventilation systems and emergency access to the tunnel when in operation.
Between them, the quartet of machines have excavated nearly 2 million tonnes of earth.
The excavated material is being used for beneficial reuse. Around 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 is being used to create new 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 by rail to beneficial reuse sites across the UK 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 build wildlife areas for birds.
The Northolt Tunnel is being built by a joint venture formed of the companies Skanska, Costain and STRABAG (SCS). The same JV will also construct the Euston Tunnel eastward from Old Oak Common to the centre of London.
Preparations to bore the final tunnel between Old Oak Common station and Euston are underway with two further TBMs due to arrive in the UK this summer ready to 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.
Caroline Hershel was an astronomer surely, not an astrologer?
Hopefully the new government will use some common-sense and give the go-ahead to the OOC to Euston leg, even if it has to be funded by central government.
I dread to think how much money was spent redesigning the new Euston station, under the pretext of looking to save money. The pause on Euston station works has probably increased costs further still.
At the very least the tunnelling and construction work for the new Euston HS2 station needs doing sooner rather than later, even if the fit out is delayed. That way other buildings can then be built on site, which might help to fund the fit out.
I wonder if it would work out cheaper to revert to the original design and if possible add in (or future-proof) a connection to HS1? That way potentially either Eurostar trains could go as far as Birmingham, or southeastern trains could depart from Euston to allow St Pancreas to expand its international travel capacity.
They have to start the tunnels to Euston to commission OOC station anyway.
No they don’t.