The most critical stage of Australia’s largest road project is due to be completed in early 2023.

Sydney’s $3.2 billion motorway will connect the M4 at Haberfield and the M8 at St Peters with up to four lanes each way, helping slash travel times.

Motorway operator Transurban is ramping up commissioning every day to get the 7.5km mega tunnels safe and ready before the ribbon is cut.

University of New South Wales construction expert, Dr Johnson Shen, said building subterranean tunnels like WestConnex is one of the most complex engineering tasks in the world.

“If we look at other highly populated cities such as Singapore or Tokyo, they have extensive networks of underground tunnels to support their above ground transport system. Why? Because when you have limited space but still need to make the city liveable for its residents, you either must start building bridges which is often impractical, or build tunnels deep below the ground,” Dr Shen said.

“No infrastructure project is ever cheap, but the benefit to the community is priceless. There are so many moving parts but ultimately, the end goal is to connect communities and make it

easier for people to move around quickly, but safely too.”

Dr Shen said an Australian record 28 road-headers were used, excavating 8.7 million tonnes of spoil, much of which was used in the construction of Sydney’s second airport.

“With bulldozer-style tracks on the road-header chassis and pineapple-like heads fitted with metal picks to excavate the rock, they have done a remarkable job in these tunnels.

“They have carved out tunnels that are wide enough for an average of four lanes in each direction with the capacity to carry up to 100,000 vehicles a day,” Dr Shen said.

Transurban’s WestConnex Group Executive, Andrew Head, said one of the little-known but most complex parts of the project was installing a massive bridging slab.

“The slab is a massive underground load-bearing structure underneath Leichhardt, that alone took 75 days to build. It involved six weeks of intense work to pour 17,000 tonnes or

close to 1,000 truckloads of concrete, and 940 tonnes of custom-made steel reinforcement,” Mr Head said.

“A prototype was developed and tested off-site first before construction started underground. We had to build it to allow one of the ramps leading to Rozelle Interchange to safely pass

overhead. Even for people who’ve worked in tunnels their whole life, this was a once in a career challenge.

“Over the last five years, almost 12,000 people have been part of an incredible team involved in building this stage of WestConnex, making it a sustainable, safe, efficient and world class operation, largely invisible to the motorist.”

Transurban will give the community a sneak peek in the tunnels, which connect the M4 at Haberfield with the M8 at St Peters, at an open day on 18 December at St Peters, with all public free underground bus tours booked out.

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