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Fri September 17 2021

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HS2 update: Video reveals progress on Chalfont ventilation shaft

23 Jul HS2 contractors are making progress digging a big hole in Chalfont St Peter, as the video below shows.

The Chalfont St Peter vent shaft under construction this week
The Chalfont St Peter vent shaft under construction this week

Five ventilation and access shafts are being construction to service HS2’s 10-mile tunnel under the Chilterns.

Following the recent launch of the two tunnel boring machines (TBMs), work has begun on excavating the first of these shafts, near the village of Chalfont St Peter.

Once complete, the 78-metre deep shaft will be topped with a headhouse designed to look like a local barn. [See our previous report here.]

Below ground level, the shaft will reach down to the twin tunnels, with fans and other equipment designed to regulate air quality and temperature, remove smoke in the event of a fire and provide access for the emergency services.

The structure is designed and built by HS2 Ltd’s main works contractor Align JV (Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick), with consulting engineers Jacobs and Ingerop-Rendel, architect Grimshaw and landscape designer LDA.

A 120-tonne drilling rig with a specialised cutting head was used to excavate the walls of the shaft, before concrete was poured in to form each of the 16 wall panels. Now, with the walls complete, the team are excavating the chalk from inside the shaft to reveal the full depth of the structure.

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The shaft will be topped by what is designed to look like a barn
The shaft will be topped by what is designed to look like a barn

The two (TBMs), Florence and Cecilia, are expected to reach this first shaft next year and complete their 10-mile journey in three years’ time. Once the TBMs have passed through, Align JV will build the internal vent shaft structures, basement works and install the equipment.

Around 18,000 cubic meters of material is expected to be excavated from the shaft, with the chalk set to be reused to landscape the site once construction is complete.

HS2 Ltd project client director Rohan Perin said: “The excavation at Chalfont St Peter shows how much progress we have already made in delivering the Chiltern tunnels.”

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