Deeper tunnels will be built under Sydney Harbour for a $5 billion motorway after the NSW government ditched earlier plans to lay large tubes in a trench on the harbour floor, allaying fears about dredging of contaminated sediment.
As foreshadowed by the Herald, the government has signed a $4.24 billion contract with Spanish company Acciona for the second stage of the Western Harbour Tunnel, which will involve using two giant tunnel boring machines between Birchgrove and Waverton to dig part of the motorway.
Premier Dominic Perrottet and Metropolitan Roads Minister Natalie Ward announce the tunnelling contract on Thursday near Balls head Reserve.Credit: Kate Geraghty
It is an about-turn on earlier plans to lay so-called immersed tubes for the three-lane tunnels on the harbour floor between Birchgrove and Balls Head, a construction method similar to that adopted for the existing Harbour Tunnel more than three decades ago.
Metropolitan Roads Minister Natalie Ward said the government had opted for deeper tunnels because it was “more cost-effective for taxpayers”, and meant that dredging of the harbour was no longer required.
“We have the more efficient, more environmentally friendly and more cost-effective option of the tunnel boring machine,” she said. “We’ve heard from the community about its concerns about dredging in the harbour.”
The initial plans to dredge the harbour to create a trench for the immersed tubes had sparked a backlash from community groups and marine experts, who feared that construction would disturb a “cocktail of chemicals” in sediment.
Balmain Greens MP Jamie Parker said the community was opposed to the toll road but any move by the government to wind back the earlier destructive design for the tunnel was welcomed. “This is a huge win for our community and comes off the back of a massive local campaign,” he said.
The $722 million first stage of the project, which involves digging 1.7-kilometre tunnels between a WestConnex interchange at Rozelle and Birchgrove, began in July. Smaller road-header equipment is being used for the stage-one tunnels.
Parts for the two massive tunnel boring machines will be transported in through the tunnels being dug between Rozelle and Birchgrove, removing the need for another site for them to enter the earth.
The boring machines will then be assembled in a large cavern under Birchgrove before they begin digging the tunnels under the harbour in 2024. They will later be disassembled in an underground cavern on the northern side of the harbour at Waverton.
Two massive boring machines similar to those used for Melbourne’s Westgate Tunnel, pictured, will be used by Acciona.Credit: Jason South
The second stage also involves using smaller machinery to dig tunnels between Waverton and the Warringah Freeway near North Sydney.
The type of boring machines needed for the project will be similar in size to that used on Melbourne’s Westgate Tunnel and feature 16.5-metre wide cutter heads – more than twice the diameter of those used to excavate tunnels for Sydney Metro’s City and Southwest metro rail line, which runs under the harbour.
North Sydney mayor Zoe Baker said the community needed more details about the changes to the project that would be necessitated by a U-turn on construction techniques.
However, she welcomed the ditching of plans to lay tubes on the harbour floor. “Finally, the state government has responded to the community concerns about the dredging of the harbour that have been raised for more than five years,” she said.
The 6.5-kilometre Western Harbour Tunnel is due to open to motorists in 2028, which is later than the original completion date of 2025-26.
The government has yet to reveal the quantum of the tolls for the Western Harbour Tunnel, which Ward said would be determined as part of a review of the entire project.
Asked what it meant for tolls on the Harbour Bridge and existing Harbour Tunnel, she reiterated that the government would “not be putting another toll” on either of the two. “Don’t believe the scare campaign from Labor,” she said.
Labor roads spokesman John Graham said the change in construction techniques would have a better environmental result, but he accused the government of rushing ahead with them without consulting communities about the knock-on effects. He also called on the government to reveal its plans for tolls for the new motorway.
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