A large sinkhole has appeared within a field above the Chiltern Tunnels being built by HS2 Ltd in Buckinghamshire.

The ground movement has occurred above a portion of completed tunnel – and tunnel operations are ongoing, as well as investigations.

HS2 Ltd is now in discussion with the landowner about the next steps and the Environment Agency has been informed of the development.

A spokesperson for HS2 Ltd confirmed: “A ground movement has occurred within a field above the Chiltern tunnels.

“Investigations are ongoing, but this is likely to be linked to pre-existing ground conditions above the tunnels.

“The site has been sealed off and there is no risk to the public.”

A total of 10km of the Chiltern Tunnel has now been completed and tunnelling operations are ongoing despite the appearance of the four-metres wide sinkhole.

The Chiltern Tunnel is scheduled to be the longest tunnel on the HS2 route between London and Crewe. 

The twin-bore tunnel is 16km (10 miles) long and will carry passengers under the Chiltern Hills.

Two Tunnel Boring Machines (TBMs), Florence and Cecilia, are being used to create the tunnel. 

The two enormous 2,000 tonne machines were delivered to their launch site at the Chiltern Tunnel South Portal, next to the M25 in Buckinghamshire, meticulously reassembled, tested and commissioned by an expert team of tunnelling engineers, before they started work on the high-speed rail project’s first tunnels.

The two TBMs that are being used to create the ‘twin bore’ Chiltern Tunnel were launched in the summer of 2021 and have passed the halfway point on their 10 mile journey under the Chilterns.