The opening of a $3.1 billion underground motorway in Sydney’s south will be delayed until the end of 2028 – three years later than previous plans – due to large sinkholes forcing tunnellers to take extreme care on a 244-metre section.
Almost 10 months after the sinkholes appeared, transport officials’ new targeted completion date for the first stage of the M6 toll road gives a clearer picture of the extent of the delay after they previously said it would be at least two years late.
Workers fill in the huge sinkhole with cement in March to stabilise the area.Credit: Rhett Wyman
Motorists using an arterial route near the main sinkhole at Rockdale face slower journey times for 18 months while ground stabilisation works are carried out. The southern section of West Botany Street near Bicentennial Park will be reduced to one lane in each direction from the middle of next year.
Transport for NSW infrastructure deputy secretary Camilla Drover said tunnelling on areas where the subsidence occurred would restart by the end of next year.
“We’re targeting opening the full project to traffic by the end of 2028. The balance of the project is still progressing well, but of course, we can’t open the full motorway tunnel until we’ve obviously finished tunnelling it out in the subsidence area,” she said.
The southern section of West Botany Street in Rockdale will be reduced to one lane in each direction for 18 months.Credit: Dominic Lorrimer
The new targeted opening of the M6 in 2028 is the same year that the $6.7 billion Western Harbour Tunnel between Rozelle and North Sydney is due to welcome its first motorists.
Work has been paused indefinitely on a 244-metre section of the M6 since March 1, when a 10-metre-wide sinkhole opened up above one of the twin tunnels at Rockdale. Days later, another emerged about 150 metres away in a construction area on the eastern side of West Botany Street.
Drover declined to put an exact date on the resumption of tunnelling next year because of the ground stabilisation works and the need to shift a major gas main and other utilities as a precaution. The resumption of tunnelling will also be subject to SafeWork NSW approval.
Contractors will inject grout into soft ground in the area to bolster its strength for when they tunnel through it. They will also use extra rock bolting and other supports.
“They’ll be going more slowly and more cautiously, and there will be more support to put in place as they do tunnel,” Drover said.
“We do not want, and the contractor has reinforced this ... any more subsidence events to occur, and safety is the most important consideration.”
The first stage of the M6 comprises four-kilometre twin tunnels between President Avenue at Kogarah and the WestConnex motorway at Arncliffe. The cost of the project blew out by $500 million to $3.1 billion in 2022.
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 timeline for the twin tunnels first slipped in 2021 by a year.
Drover said the extra work and time needed to complete the M6 would increase the project’s cost further, but it was too early to put a figure on it.
“Whether government contributes to that additional cost, that will be the subject of those complex legal and insurance processes,” she said.
Drover said the reduction in lanes on West Botany Road for 18 months would cause traffic delays, but the effects could be reduced by the completion of an upgrade to nearby President Avenue to three lanes in each direction by the middle of next year.
About five kilometres of new shared pathways for pedestrians and cyclists are on track to be completed by the end of 2025.
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