HS2 Ltd has revealed designs for the final new tunnel in the Chilterns as work is progressing across all five sites.

The tunnel is located in the rural landscape of the Chiltern Hills with the headhouses based on a ‘barn design’ to fit in with the scenery.

Work has now started at all five locations with excavation well underway for the 10-mile Chiltern tunnel, which is going to be the longest tunnel in the HS2 project.

The Chesham Road headhouse is mostly concealed by a hedge and line of mature oak trees along the B485 with its design intended to fit in with the surrounding landscape being similar in style to the local barns and agricultural structures in the area.

The headhouse is a single-story structure and will be wrapped in a pre-weathered grey zinc roof which will age naturally over time whilst maintaining its toughness. The entire building will sit on a dark blue brick base.

Underground, a 45m shaft will connect to the twin tunnels and give emergency services access. Chesham Road’s headhouse location is close to the North Portal of the tunnel and will not require ventilation like the other four shafts.

HS2 Ltd’s main works contractors Align JV have drawn up plans working alongside Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick. The design aspect was also completed working with partners Jacobs and Ingerop-Rendel and architect Grimshaw, with LDA providing landscape designers.

The Chiltern tunnel needed to be extended by 2.6km so during 2015 the Chesham Road shaft was added. This design change was welcomed as it meant saving 12 hectares of woodland at Mantle’s Wood, Sibley’s Coppice, and also Farthings Wood.

Two massive boring machines (TBMs) were put in motion earlier in 2021 and are digging parallel tunnels northbound and southbound. The TBMs have now passed beneath the M25 and are making their way to the site of the first shaft, which is situated at Chalfont St Peter. Engineering experts from Align are underway with the excavation of the shaft, which is currently at 68m deep and is expected to be fully complete before the arrival of the first TBM in 2022.

HS2 has also completed concrete ‘diaphragm walls’ at the 46m deep shaft located near to Chalfont St Giles. The team has used specialist drilling equipment and will begin excavating material from within the concrete walls, allowing them to create the shaft.

The location of the next shaft site is right next to the A413 junction outside of Amersham. Engineers are well underway with the concrete ‘D-walls’ for the 51m shaft. Heading north at the Little Missenden site which is further along, the A413 engineers have begun preparation work for wall construction and Chesham Road, which is the last shaft on the TBMs tunnelling journey is also advancing well. 

Communities have been given the chance to make comments on the Chesham Road headhouse design, which they can do by attending an online information event that will run on Wednesday the 8th of September.

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.”

Daniel Altier, Align Project Director, 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 receiving comments on the design from the local community.”

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