Complex tunnelling to carve out part of a $3.1 billion underground motorway in Sydney’s south has been delayed until late next year after a major sinkhole halted work more than six months ago.
Facing significant engineering challenges, senior transport officials are engaged in high-stakes negotiations with insurers and the contractor building the motorway over design changes to the twin road tunnels at Rockdale.
Work has been paused indefinitely on a 244-metre section of the first stage of the M6 toll road since March 1 when a 10-metre-wide sinkhole suddenly opened up above one of the twin tunnels, leaving a two-storey building at risk of collapse and forcing workers to evacuate.
The sinkhole opened on March 1 above one of the tunnels at Rockdale for the M6 motorway.Credit: Fire and Rescue NSW
Quizzed about whether tunnelling on the affected section was likely to resume in the first half of next year, Transport for NSW infrastructure deputy secretary Camilla Drover said she thought it would be “later in 2025”.
“There is quite a complex process to work through. No one is going to recommence tunnelling in that area until we are satisfied that it is safe,” she told a budget estimates hearing. “There are roads above that precinct ... so there’s some complexity to be worked through.”
A tunnel redesign will increase the project’s cost and require a detailed and potentially lengthy approval process.
The motorway had previously been scheduled to open to motorists by the end of 2025, which was already later than the original completion date of this year. The first stage of the M6 comprises twin three-lane tunnels extending from Kogarah to the WestConnex motorway at Arncliffe.
Drover said a redesign of the affected section of tunnels was required, which would determine the extent of the delay. She added that the implications of the delays and tunnel redesign on the project’s cost were the subject of complicated legal, commercial and insurance processes.
“Obviously, the insurance processes are under way, as are discussions, but it will be a function of the investigation and the way forward more generally,” she said.
The cost of the four-kilometre motorway blew out by $500 million to $3.1 billion in 2022.
Once the new tunnel designs are decided, Drover said the local council and other community stakeholders would be consulted, and necessary approvals sought, along with the green light from WorkSafe for the prohibition on tunnelling to be lifted.
Workers fill in the huge sinkhole with cement in March to stabilise a two-storey building which teetered on the edge. Credit: Rhett Wyman
She declined to comment on who would bear the construction risk. Transport for NSW has contracted a joint venture among contractors CPB, UGL and Ghella to build the motorway.
Coalition roads spokesperson Natalie Ward said the lack of detail provided by the government about the project was concerning. “Worker safety always comes first in a situation like this. The next step is to understand the impacts to the project and ultimately to the taxpayer,” she said.
Just over a week after the major sinkhole opened up on March 1, another emerged about 150 metres away in a fenced-off construction area on the eastern side of West Botany Street, near one of the main entry points.
While construction on the Rockdale section has stopped, work on the rest of the motorway, including tunnel lining and electrical fit-outs, is proceeding.
Start the day with a summary of the day’s most important and interesting stories, analysis and insights. Sign up for our Morning Edition newsletter.