Last week on August 8th, 2023 the giant TBMs reached the Little Missenden ventilation shaft, passing the fourth of five ventilation and emergency access shafts, 75% of the way through the 16 km (10 mile) long Chiltern tunnel.
The enormous 2,000 t machines have spent two years excavating the twin tunnels between the M25 and South Heath in Buckinghamshire that will help improve connections between London, Birmingham and the North.
Each machine is a 170m long self-contained underground factory, digging the tunnel, lining it with 56,000 concrete segments to form rings and grouting them into place as it moves forward.
Designed specifically for the geology of the Chilterns, the first TBMs were launched in Summer 2021 from a site near the M25 and have already excavated approximately 2 million cubic metres of chalk and flint.
The excavation of five shafts have also been completed, and they will provide ventilation and emergency access near Chalfont St Peter, Chalfont St Giles, Amersham and Little Missenden with an intervention shaft at Chesham Road.
The 35m deep shaft near Little Missenden – which the TBMs have now reached – is next to the A413 about half a mile from the Buckinghamshire village.
A ‘headhouse’ will be built on top of the shaft to house ventilation and safety equipment, designed to resemble local farm buildings with new planting to help blend it into the surrounding landscape.
The news comes just weeks after planning consent was granted by Buckinghamshire Council for the North Portal of the tunnel under Schedule 17 of the HS2 Act, meaning that all major design elements now have consent.
The two TBMs are operated by, Align – a joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
HS2 currently has five TBMs in the ground, with a further five due to be launched over the coming years. Together they will create 103 km (64 miles) of tunnel between London and the West Midlands including major tunnels on the approach to London and Birmingham.
Click here for a video, here and uk/65 for tunnelbuilder archive. Visit https://www.hs2.org.uk/. 32/23.
