HS2 Chiltern Tunnel sinkholes appear in Buckinghamshire

Sinkholes thought to be caused by the boring of tunnels for the HS2 rail project have opened up in a field.

Two new holes were discovered on land on the outskirts of South Heath, near Great Missenden, Bucks, where the Chiltern Tunnel is being constructed.

It means four craters have been caused by HS2 in the county in nine months.

HS2 Ltd said "safety was its top priority" and both sinkholes had been fenced off amid ongoing tunnelling operations.

The smaller of the two holes was found next to Frith Hill during routine monitoring on 7 February, with a larger feature found in the same field five days later, according to the Local Democracy Reporting Service.

There was no public right of way across the affected land, HS2 Ltd said.

HS2 Ltd said the latest sinkholes may have been caused by disturbance from tunnelling and recent rainfall that exposed existing weak spots.

"We have always recognised that the geology of this part of the route is particularly challenging - with poorer quality, less stable chalk susceptible to ground movement," a spokesman said.

"Temporary fencing has been installed and extra monitoring put in place."

The 10-mile (16km) Chiltern Tunnel is the longest on the HS2 project, which aims to improve links between London and Birmingham.

Buckinghamshire Council and the Environment Agency have been approached for comment.