Australia – A TBM mining the Forrestfield-Airport Link in Perth, Western Australia was stopped on 14 February. Ground disturbance was detected prior to the TBM entering an area of ‘critical airport infrastructure’ and the client is describing the move as a temporary safe guard.

A spokesperson for the project said, “Perth presents challenging geological conditions for tunnelling, with some elements of uncertainty to be expected in adapting the TBMs to varying ground conditions. The Ascot Formation, through which the TBMs were tunnelling when disturbance occurred, comprises non-cohesive granular material that makes tunnelling more complex.”

It was stressed that all parties were aware of this risk.

“An extensive network of ground monitoring equipment has also been installed along the rail route to provide updates in near real time regarding any ground movement at the surface. If anomalies occur in the TBM’s readings a precautionary spotter is deployed to the surface to survey the area. As an added precaution the area may be cordoned off until it can be confirmed that no ground disturbance will occur.”

The Public Transport Authority and Perth Airport have engaged independent experts as part of the review of tunnelling operations. The contractor, Salini Impregilo-NRW is running detailed risk workshops to determine any lessons that can be incorporated into tunnelling operations. A specialist advisor from Herrenknecht has also reviewed operations and provided recommendations for improvement.

Once the review is complete, tunnelling will recommence. However, no timeline was given. The contractor declined to comment.