Excavation of the twin-bore Northolt tunnel between West Ruislip at the outer edge of the capital and the new Old Oak Common super-hub station in west London has been completed.
On 26th June TBM Anne, the fourth of four TBMs being used to dig the Northolt tunnel, 13.5 km (8.4 mile) long, installed the final concrete ring underground before emerging into a vent shaft at Green Park Way in Greenford.
TBM Anne, named after Lady Anne Byron, was launched in April 2024 and has spent 14 months underground mining the second bore of the 3.4 mile eastern section. At its peak, the 1,700t and 9.11 m diameter TBM advanced at around 38 m per day.
The tunnel segments - each weighing up to 7t - used by TBM Anne were made in Hartlepool by STRABAG and were transported to site by rail thereby minimising usage of London’s busy road network.
The Northolt tunnel, which is 35 m below ground at its deepest point, has been bored by HS2’s London tunnels contractor Skanska Costain STRABAG JV (SCS JV). The inside width of the tunnel varies between the eastern and western section 8.10m in the east and 8.80m in the west. The tunnels for HS2 are wider for the sections of the route where the trains run faster given aerodynamic needs.
Northolt is one of five deep twin-bore tunnels on the 140-mile route and the second longest behind the Chiltern Tunnel, which is 10 miles long.
Now the tunnel excavation is complete, the team will continue to build the flat tunnel invert on the base, creating a flat surface where high speed tracks will be laid. There will also be 34 cross passages mined between the two bores of the tunnel which the team continue to build.
The team are also completing five headhouses on the surface of the tunnel. The headhouses cover the ventilation shaft which connects the HS2 tunnel to the open air. It regulates air quality and temperature in the tunnel and allows smoke to be extracted in the event of a fire. The headhouse is the building on top of the ventilation shaft which contains fire control systems and the ventilation systems for the railway tunnels below.
For further information about the project click here and uk/65 for tunnelbuilder archive and visit https://mediacentre.hs2.org.uk. 26/25.
