The first images of HS2's 'barn design' rural headhouses which will provide emergency access to the 10 mile long Chiltern tunnel have been unveiled.

The reveal of the design completes the set of five headhouses on the Chiltern tunnel, with work now begun at all sites and excavation well underway for what will be the longest tunnel on the HS2 project.

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.

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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.

HS2 Project Client Rohan Perin said: "The launch of our giant tunnelling machines – Florence and Cecilia – earlier this year were huge symbolic moments for the project, but just as important has been the progress we’ve made at each of the shaft sites to prepare for the arrival of the TBMs over the next three years.

"The reveal of the first designs for Chesham Road complete the set of five headhouse designs. As with each of the other rural headhouses, our priority has been to blend the buildings into the surrounding landscape, and I look forward to seeing what the local community thinks of the plans."

The Chesham Road shaft was added to the Chiltern tunnel in 2015 in order to allow the tunnel to be safely extended by 2.6km – a decision which saved 12 hectares of woodland at the nearby Mantle’s Wood, Sibley’s Coppice and Farthings Wood.

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.