A 500-tonne ‘concrete plug’ has been poured into a sinkhole to plug it after it was created by TBM work on Melbourne’s North-East Link tunnel.
Investigations revealed that a planned test during excavation of the tunnel caused the ground at a sports oval to cave in on the 6th of January. This caused an eight-metre-wide sinkhole which ABC News reported had been “preventable”.
It was described by VIDA Roads as “a very serious incident” due to “a test that should not have taken place” despite the tunnel boring maching (TBM) crew following the correct procedure. VIDA Interim CEO Paul Roth said the North-East Link TBM had entered an area that was geologically complex and fragmented.
“This was not a surprise; we were aware of the conditions, we had excellent information about the conditions, and the TBM was operating as expected,” he said.
The crew then pushed past this area of complex and fragmented earth in line with procedure. It was at this point the crew conducted a planned test which reduced the pressure within the TBM so workers could enter the machine to do maintenance. However, the pressure test destabilised the ground, causing the sinkhole. The test had been planned to familiarise crews with the process before they crossed the Yarra River.
Mr Roth said controls and processes are being tightened to make sure such a decision would not happen again. There would now be crews on the surface during tunnelling operations to identify any movement and create an exclusion zone if necessary.
He went on to say that the Victorian Government was working with its construction partners to ensure any such incident would happen again. Following the concreting of the sinkhole, turf will be applied and the oval will reopen in March.
Image source: Aaron Lee (via ABC News).
About the author
Desi Corbett
Desi is the Editor of Concrete in Australia, at the helm since December 2013, and our weekly news writer since 2016. Focused on concrete and construction for more than 11 years, her expertise in this field forms part of a journalism career spanning three decades. To get in touch please email desi@corbettcomms.com