HS2 reveals designs for final Chiltern tunnel headhouse as work now underway at all five sites

HS2 has revealed the first images of the latest of its ‘barn design’ rural headhouses, which will provide emergency access to the 10 mile long Chiltern tunnel. The reveal of the design completes the set of five headhouses on the Chiltern tunnel, with work now having begun at all sites and excavation well underway, for what will be the longest tunnel on the HS2 project.

HS2_Chesham Road headhouse_sm.jpg
HS2_Chesham Road headhouse_sm.jpg

Largely hidden behind a hedge and line of mature oak trees next to the B485, the Chesham Road headhouse is designed to fit into the surrounding landscape and takes its inspiration from the style of nearby barns and other agricultural buildings.

The single-story building will be wrapped in a simple pre-weathered grey zinc roof, which will age naturally over time, without loss of robustness or quality, while the whole structure will sit on a simple dark blue brick base.

Below ground level, a 45m shaft will reach down to the twin tunnels below, to provide access for the emergency services. Because of its proximity to the North Portal of the tunnel, unlike the other four shafts, Chesham Road will not need to include ventilation equipment.

The plans were drawn up by HS2 Ltd’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick - working with its design partners Jacobs and Ingerop-Rendel, and the architect Grimshaw and landscape designers, LDA.

Daniel Altier, project director for Align, said: “I am delighted with the progress we have made so far, at all five shaft sites. We are working to a detailed schedule to ensure that each shaft is ready for the arrival of our two TBMs, currently tunnelling north from the South Portal.

As is the case with all the shafts, it is important that the headhouse design at Chesham Road fits into the surrounding landscape, therefore we look forward to receiving comments on the design from the local community.”

Construction of the tunnel is now well underway. The two giant tunnel boring machines (TBMs) that were launched earlier this year to dig the parallel northbound and southbound tunnels have now passed under the M25 and are heading towards the first shaft site near Chalfont St Peter. An expert team of engineers from Align have already excavated the shaft to a depth of 68m and are working to complete it before the arrival of the first TBM next year.

At the next shaft site, near Chalfont St Giles, the HS2 team have now completed the concrete ‘diaphragm walls’ for the 46m deep shaft using specialised drilling equipment and will soon begin excavating material from within the concrete walls in order to create the shaft.

The next shaft site is next to the A413 road junction outside Amersham. Work is well underway, with engineers working on the concrete ‘D-walls’ for the 51m deep shaft. Further north at the Little Missenden site, alongside the A413, engineers are preparing for the start of wall construction, while at Chesham Road - the last shaft the TBMs will reach - site set up is now well underway.