In order to excavating the twin tunnels between the M25 and South Heath in Buckinghamshire and creating the longest tunnels on the new high-speed rail line, the two Florence and Cecilia Herrenknecht machines with 10.2m diameter, were commissioned 18 months ago and currently these TBMs have passed the halfway point on their 16km journey beneath the Chilterns.
Additionally, the ventilation and emergency access near Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden, as well as the Chesham Road is due to be provided by excavated five shafts, while the engineers recently completed the first breakthrough from a cross passageway to the shaft at Chalfont St Peter.
The amount of excavated chalk and flint is over than 1.3 million m3 and they will be used as part of a chalk grassland restoration project at the south portal of the tunnel.
The intention is transportation of high-speed trains between London and the north at speeds of up to 320km/h, following completion of the Chiltern tunnels.
The responsibility of advancing the Chiltern tunnel and nearby Colne Valley Viaduct is up to HS2’s main works contractor, Align, which is a joint venture of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
According to Align's underground construction director, Didier Jacques: "Passing the halfway point, on what was a long drive for the TBMs, was a great achievement and he paid credit to supply chain partner TGT whose personnel were manning the TBMs."
"This significant progress would not have been possible without the supporting teams on the surface at the south portal, who supply the thousands of 8.5-tonne segments required to line the tunnels, process the spoil pumped back as slurry through our slurry treatment plant and landscape the chalk produced across the site. Overall, a great team effort," added Jacques.
Digging separate tunnels for north and southbound trains, these two identical TBMs have been designed for the mix of chalk and flints under the Chilterns, whereas their daily performance is about 15m and have installed 56,000 fiber-reinforced concrete segments.
In order to commencing the project’s London tunnels, HS2 recently launched two TBMs and celebrated the first breakthrough with the completion of the first of two tunnels under Long Itchington Wood in Warwickshire.