By rosebell
Through one of four TBMs building the Northolt Tunnel breaking through at Ealing, HS2 has completed an 8km tunnel drive beneath London.
As the second machine to reach the Green Park Way vent shaft in Ealing,TBM Caroline is 2,050-tonne and broke through into an underground reception can filled with foam concrete and for completing the 8km stretch of tunnel installed the 4,217th concrete tunnel ring.
Due to the high water pressure in the ground at the site, HS2 is using the reception can method for the breakthrough, and this method can allows the TBM to maintain pressure while sealant can be applied from the tunnel lining, preventing water ingress. Then the reception can depressurised before it is opened and the TBM is lifted out.
In order to constructing the Northolt Tunnel, four Herrenknecht TBMs are being used which includes a 13.5km twin-bore tunnel that is due to take the high-speed trains from West Ruislip into the new Old Oak Common super-hub station in west London, whereas building the western section of the tunnel is up to TBMs Caroline and Sushila while two more are excavating the eastern leg. All are being lifted out of the ground at Green Park Way.
December 2024 was the date of completing the journey of TBM Sushila, that is the first machine to be commissioned for this stretch of the HS2 route, and it has subsequently been lifted out from the ground at Green Park Way using a gantry crane. Also construction of the eastern section of the tunnel from HS2’s Victoria Road Crossover Box just outside the Old Oak Common station site is currently undergoing by two further machines.
In total 93% of the Northolt tunnel has been built, and the two further machines will complete their journeys later this year.
While HS2 chief executive Mark Wild undertakes a comprehensive review of the project and aim to report a fundamental reset of the program to ensure the project is delivered efficiently and at the lowest possible cost, work on construction of the high-speed line continues.
According to HS2 Ltd client director Malcom Codling: “We are 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.”
Responsibility of building the route through London is up to HS2’s London tunnels contractor, Skanska Costain Strabag joint venture (SCS), which totally involves 20.7km of twin-bore tunnels, including the Northolt Tunnel and the Euston Tunnel, which is eventually going to take the railway from Old Oak Common station into HS2’s central London terminus at Euston. The scheduled date for commencing the excavation process of the Euston Tunnel is next 12 months.Additionally, for providing ventilation and emergency access to the tunnels, SCS will build eight vent shafts and headhouses.
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. 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.”
Currently that the two western TBMs have completed their journeys, SCS JV is slated to continue to work in the 8km stretch of the Northolt Tunnel to construct 20 cross-passages between the two tunnel bores, whereas the team will also install tunnel inverts and complete the tunnel walkways.
Involving five deep, twin-bore tunnels for this project between London and the West Midlands, HS2 has already completed the digging process 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.
