Chalk laid out near the south portal of the Chiltern tunnel - summer 2022, Via HS2

HS2 lay first million cubic metres of chalk for the Chiltern grassland transformation

The grounds of the Chiltern Tunnel, HS2’s largest construction site, is being transformed into a wildlife haven as the project has reached a major milestone through the millionth cubic metre of chalk laid out around the south portal.

The project will aim to culminate with the eventual excavation of see 2.6 million cubic metres of chalk during the construction of the 10-mile-long tunnels, thus creating one of the largest areas of chalk grassland in the Chiltern hills. Instead of transporting these materials away from the site and construction process further, they will be utilised to landscape the site as part of plans to create 127 hectares of new chalk grassland, woodland, wood pasture and wetland habitats.

The chalk grassland of the site acts as a habitat of international conservation importance as it comes in Lime-rich, but low in nutrients, thin soil that holds little water and drains well. These conditions afford a vast variety of small herbs and wildflowers whilst hosting over 40 plan species, including some of the UK’s rarest orchids as well as highly diverse invertebrate populations

Welcoming the news, HS2 Ltd.’s Environment Director Peter Miller said:

“The south portal project is one of the most important parts of our Green Corridor programme to establish better connected, sustainable and biodiverse landscapes along the route of the new railway and will contribute substantially to HS2’s carbon reduction target.

“It’s great to see how much chalk has already been laid on site and I look forward to seeing the site completely transform over the coming years.”

This project is seeing the implementation of two giant tunnelling machines that are currently 4 miles deep into their journey under the Chilterns. This process produces mass amounts of materials that require excavation, which is then mixed with water to form a slurry before being pumped out of the tunnel. This slurry is then processed at a treatment plant which sees the removal of flint and water to leave chalk cake. The chalk is then carefully laid out on site along with concrete and aggregates recycled from constructions works, creating a naturalistic landscape with all the temporary construction buildings removed.

The environmental sustainability of the project is furthered with ninety hectares of chalk grassland being seeded into re-profiled soil layers. This will then be partnered with new areas of woodland, wood pasture and wetlands, including almost 65,000 trees and shrubs of 32 species and nearly 3.5km of new hedgerows.

As the UK strives towards achieving net-zero by 2050, HS2 has been at the forefront with environmentally decarbonised construction methods such as this. Their efforts should be mirrored across the sector wherever possible as a greener railway expands throughout the nation.

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