The Chalfont St Peter Ventilation Shaft, or headhouse, will provide ventilation and emergency access to a 10-mile-long train tunnel through the Chilterns – a set of hills to the northwest of London.
As the Chilterns are a designated Area of Outstanding Natural Beauty (AONB), Grimshaw has proposed a design that will disguise the piece of infrastructure as a simple agricultural building.
Set back from the main road, the Chalfont St Peter Ventilation Shaft will look like a smart barn, clad in industrial grey zinc with deep bronze accents on the doors and vent openings. The zinc will be pre-weathered and will darken over time, complimenting its plinth of blue-toned bricks.
Underneath, a 60-metre shaft will reach down to the HS2 railway tunnel below.
"Chalfont St Peter Ventilation Shaft has been sensitively designed to complement the rural character of the Chilterns," said Grimshaw associate principal Diane Metcalfe.
"The position and orientation of the headhouse buildings are located to conceal them within the landscape and form a courtyard similar to local farmyard arrangements," she added.
"The pitched roof, zinc-clad buildings are a modern interpretation of the local agricultural and industrial vernacular."
To minimise disruption, the material created from excavating the shaft will be used to re-landscape the area around the headhouse, instead of being removed by lorries.
Mature trees around the perimeter will be preserved, and bird boxes will be built to encourage local wildlife to return to the site after construction is over. Grimshaw has also included reptile-basking banks for lizards to sun themselves, a hibernaculum for animals to shelter in over winter, and an egg-laying heap for grass snakes.
The proposal is the result of "close and collaborative" work with the AONB's review group, said Grimshaw. Local residents will now have a month to give their feedback on Grimshaw's design.
Grimshaw is also designing a station for HS2 at Birmingham Curzon Street. The Y-shaped railway line will link up London, Birmingham, Manchester and Leeds with high-speed rail service and is due to complete in phases between 2029 and 2035.
Founded by Nicholas Grimshaw in 1980, Grimshaw is also currently designing an arts complex for the Santa Monica College campus and proposals for coronavirus testing centres built in converted shipping containers.