The 13.5km-long tunnel runs underground between West Ruislip Victoria Road in Ealing, west London – just outside HS2’s Old Oak Common station. At its deepest point, it is 35m below ground. The tunnel was constructed using four TBMs and excavation was finished[https://www.tunnelsandtunnelling.com/news/hs2-completes-northolt-tunnel-excavation/] in June last year.
The mined cross-passages, which range from 6-20m between the northbound and southbound tunnel bores, were made using sprayed concrete lining (SCL).
Ground freezing was used on 11 of the cross-passages because of the presence of water-bearing soils with a high water table in the ground in the western section of the tunnel. This required the team to insert freeze pipes through special tunnel segments to create a 2m-thick freeze wall to stabilise the ground before excavation could take place.
Now construction of the cross-passages is completed, reinforced concrete secondary collars will be installed to form the permanent openings for doors and enable the installation of permanent fire-rated sliding doors.
It is expected that all structural works on the tunnel – the second longest on the 225km route between London and the West Midlands – will be completed later this year. The tunnel will then be readied for installation of the rail systems such as tracks and overhead power in the coming years.
HS2’s project client, Malcolm Codling, said completing the construction of the cross-passages was an important step towards finishing the civil engineering on the tunnel.
Booth Industries in Bolton is manufacturing the doors for all the tunnels on the HS2 route. High-speed trains will pass within metres of the doors which will be capable of withstanding constant 14Kpa pressure cycles, along with two-hour integrity and two-hour insulation against fire. They are being manufactured using mainly UK-made steel.
