HS2 has today completed an 8km tunnel drive under London, with one of four TBMs building the Northolt Tunnel breaking through at Ealing.
TBM Caroline is the second machine to reach the Green Park Way vent shaft in Ealing. The 2,050-tonne TBM broke through into an underground reception can filled with foam concrete and installed the 4,217th concrete tunnel ring to complete the 8km stretch of tunnel.
HS2 is using the reception can method for the breakthrough because of high water pressure in the ground at the site. The reception can allows the TBM to maintain pressure while sealant can be applied from the tunnel lining, preventing water ingress. The reception can is then depressurised before it is opened and the TBM is lifted out.
Four Herrenknecht TBMs are being used to build the Northolt Tunnel – a 13.5km twin-bore tunnel that will take the high-speed trains from West Ruislip into the new Old Oak Common super-hub station in west London. TBMs Caroline and Sushila have built the western section of the tunnel while two more are excavating the eastern leg. All are being lifted out of the ground at Green Park Way.
TBM Sushila, the first machine to be launched for this stretch of the HS2 route, completed her journey in December last year and has subsequently been lifted out from the ground at Green Park Way using a gantry crane. Two further machines are currently building the eastern section of the tunnel from HS2’s Victoria Road Crossover Box just outside the Old Oak Common station site.
In total 93% of the Northolt tunnel has been built, and the two further machines will complete their journeys later this year.
Work on construction of the high-speed line continues as HS2 chief executive Mark Wild undertakes a comprehensive review of the project. His work will lead to a fundamental reset of the programme to ensure the project is delivered efficiently and at the lowest possible cost.
HS2 Ltd client director Malcom Codling said he was proud of the work done to complete the second breakthrough for the Northolt Tunnel.
“As we focus on delivering Britain’s new high-speed railway between London and the West Midlands, we are gearing up for our most productive year to date on this stretch of the line,” he said.
HS2’s London tunnels contractor, Skanska Costain Strabag joint venture (SCS), is responsible for building the route through London. In total, this involves 20.7km of twin-bore tunnels, including the Northolt Tunnel and the Euston Tunnel, which will eventually take the railway from Old Oak Common station into HS2’s central London terminus at Euston. Excavation of the Euston Tunnel is expected to start in the next 12 months. SCS will also build eight vent shafts and headhouses – providing ventilation and emergency access to the tunnels.
SCS managing director Richard Adams said the completion of the western section of the Northolt Tunnel was a testament to the dedication and skill of all the joint venture’s teams.
“Later this year two more TBMs, Emily and Anne, will finish their journeys, which will complete the 8.4-mile (13.5km) Northolt tunnel between Old Oak Common and West Ruislip,” he said.
“Work on the cross-passages, tunnel walkways, ventilation shafts, headhouses and portals continues at pace as our team works at peak productivity to deliver our part of HS2, that will bring better journeys and boost economic growth.”
Now the two western TBMs have completed their journeys, SCS JV will continue to work in the 8km stretch of the Northolt Tunnel to construct 20 cross-passages between the two tunnel bores. The team will also install tunnel inverts and complete the tunnel walkways.
In total, five deep, twin-bore tunnels are being built for HS2 between London and the West Midlands. HS2 has already completed the excavation of two of its tunnels – the 16.1km Chiltern Tunnel and the 1.6km Long Itchington Wood Tunnel in Warwickshire.
HS2 is also preparing two further TBMs to build the Euston Tunnel after the Chancellor gave the green light in the budget last year.
