TBM Sandy stopped when it came within 40m – the minimum distance – of the stationary TBM Grace.
Grace stopped tunnelling on February 14 after encountering some minor ground disturbance issues when travelling through difficult terrain, the Ascot formation.
Though Sandy has not experienced the same ground disturbance issues, it is widely-accepted best practice that two TBMs should not be positioned side-by-side during tunnelling.
The tunnelling contractor is undertaking a detailed review of their operating procedures as a result of the incidents with Grace. Specialist advisers from the TBM manufacturer have visited the site to review tunnelling operations.
An independent international expert has been engaged to review tunnelling procedures and ensure lessons learned are incorporated into operations.
The Public Transport Authority, contractor Salini Impregilio - NRW and Perth Airport are working closely to allow full tunnelling operations to resume as soon as possible.
It is expected that Grace – and subsequently Sandy – will be able to resume tunnelling in the coming weeks, once a number of investigations into the earlier ground disturbances are complete.
Meanwhile, work continues on the construction of Airport Central Station and the dive structure at Bayswater Junction.
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