Two TBMs on HS2 project completed the first stages of their drives earlier this year on the Chiltern Tunnel by reaching the 78m deep ventilation shaft at Chalfont St Peter, which will also provide emergency access to the high-speed rail tunnels in future.
Chiltern tunnel will have five structures to provide ventilation and emergency access, all of which are being carefully nestled into the landscape with their headhouse designed to have minimum visibility while complementing the surroundings.
HS2 recently unveiled its updated design for the headhouse at the 38m deep Amersham ventilation shaft, in Buckinghamshire, where shaft construction is complete. The curved headhouse of the shaft will be one of the few parts of the project visible above ground. The revised design lowers the height by 2m as well as changes the steel fins on top to have pre-patinated zinc panels that more match the natural tones of the landscape. Further changes to surrounding landscaping is to make more use of natural stone, naturally occurring in the chalk hills of the Chilterns.
Main works contractor on the Chiltern Tunnel is Align JV, a team of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick. Design partners are Jacobs and Ingerop-Rendel. Architect is Grimshaw. Landscape designer is LDA Design.
Align JV’s technical director, Alan price, said: “It has been essential for our designers to listen to the local stakeholders to understand what is important to them, and to update the design accordingly. We believe the jointly developed new design sits more comfortably within its surroundings.”
In London, earlier this year, main works contractor SCS JV (Skanska, Costain, Strabag) completed a key part of main shaft tunnelling works at Victoria Road site, in Acton, which will serve the Northolt Tunnel. The site also involves construction of a crossover box for trains to switch tracks outside the future Old Oak Common station. Northolt Tunnel will see a total of eight ventilation shafts constructed.
While tunnelling has been underway across the multiple works sites, tunnelling was farthest ahead at Victoria Road site. The 25m i.d. ancillary shaft will be the launch site for two TBMs to bore the eastern section of the main tunnels, the drives scheduled to commence in late 2023.
Work on the Victoria Road shaft began in February 2021with construction of a 160m3 concrete collar, following which precast concrete segmental lining, supplied by F P McCann, was used for the first 11m depth. Sprayed concrete lining (SCL) was used for the remaining depth of 19m.
The 3.3m thick base slab was placed in three pours over the winter, the main pour being 1000m3 and the remaining pours adding a further total of 740m3.
For the future tunnelling works, the site is to be connected by spoil conveyor with Old Oak Common site and the logistics hub at Willesden Euroterminal.
