By lyndamyer
In order to surveying the surface hole that appeared above an HS2 tunnel in Buckinghamshire on 13 May, investigations are undergoing.
While the announced wide for the hole above the Chiltern Tunnel was 5-6m by initial reports, currently HS2 says it is almost 4m wide and 3-4m deep and the geology in the area is chalk.
An HS2 spokesperson told T&TI: “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.”
Considering that the hole is above a completed section of tunnel so tunneling operations have not been affected.
The Environment Agency has been informed and HS2 is discussing plans with the landowner.
As the longest tunnel on the high-speed rail line, the twin-bore Chiltern Tunnel is 16km long. Being commissioned in summer 2021, the two 10.26m diameter Herrenknecht TBMs – Florence and Ceclia – were reached the halfway mark in February.
HS2’s main works contractor, Align – a joint venture of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick – is responsible for the Chiltern Tunnel and nearby Colne Valley Viaduct.
Due to appearance of pools of foam above the tunnel on Ruislip Rugby Football Club land, the tunneling process on the 8km-long tunnel from West Ruislip to Greenford was halted earlier this year. The HS2 spokesperson told T&TI that tunneling resumed a few weeks ago and main works contractor SCS (Skanska Costain Strabag) was continuing to monitor the area.
