Images curtesy of North East Link Project
Images curtesy of North East Link Project
Images curtesy of North East Link Project
- The North East Link will connect two major highways in the northeast of Melbourne.
- The project will remove up to 15,000 trucks from local roads, reducing CO2 emissions, congestion, and travel times
- The TBMs have begun the excavation of the state’s longest road tunnel
- The maximum excavation depth will be 45 meters when the two TBMs pass under the Yarra River
With its engine coming to life on a recent August day in the Melbourne suburb of Watsonia, a massive tunnel boring machine (TBM) surged forward from its launch box, pushing its rotating cutterhead into the ground.
It was the start of a journey that will see the TBM excavate a tunnel of 5.5 kilometres under roads, houses and near an army barrack as part of the biggest road project in the history of the Australian city: the North East Link.
Under the Yarra river
At one point, TBM Zelda, named after an activist for equal pay among the sexes, will go as deep as 45 metres to pass under the Yarra River, a famous waterway that flows through the city from the northeast into Port Phillip Bay.
After resurfacing near the intersection of Lower Plenty Road and Greensborough Road, it will resume its underground journey to reach the suburb of Bulleen 3.3 kilometres to the south.
Parallel tunnels
The Zelda TBM is not alone in the arduous task of of digging beneath Melbourne. A second TBM, named Gillian in honour of the founder of the country’s first breast milk bank, joined it. It started from the same work site in Watsonia excavanting a parallel tunnel some seven metres apart from Zelda’s.
They are the same type of TBM called Earth Pressure Balance, or EPB, which works best in the soft rock to be encountered underground.
Among the world’s largest
With cutterheads 15.61 metres in diameter, they are among the largest in the world. With all the machinery that they trail behind them, Zelda and Gillian are as long as a small train at more than 90 metres – and they weigh nearly as much at more than 4,000 tonnes each. The cutterheads themselves come in at 400 tonnes each.
They use powerful hydraulic cylinders to push their rotating cutterhead against the ground before them. The discs on the face of the cutterheads grind away at the ground and transport the rock and soil – or spoil – by a screw conveyor from the excavation chamber to a series of conveyor belts to a spoil shed where the excavated material is taken away by trucks. In one single advance of 2.4 metres, the TBM produces 1,150 tonnes of spoil.
Zelda and Gillian will line the walls of their respective tunnels with precast concrete slabs as they go. Apart from the deep passage under the Yarra, they will mostly be working at 25 metres under the surface. The finished tunnels will actually be 6.5 kilometres long, with the remaining to be completed by machinery like road-headers.
Longest in the state
Once completed, the tunnels will be the longest of their kind in the state of Victoria, where Melbourne is the capital. They will each have three lanes for vehicle traffic. This important part of the North East Link project is being completed by the Spark North East Link Design and Construct Joint Venture, which includes Webuild, the Italian civil engineering group that is a global leader in tunnelling.
The entire project will provide what has long been called the missing link in the city’s road network. The tunnels will connect the M80 Ring Road to the north with the Eastern Freeway to the south.
More than 6,700 people are working across the project. Before its scheduled completion in 2028, an estimated 12,000 jobs will have been created.
The North East Link belongs to the Big Build, an ambitious state government programme that includes a series of major public works designed to help Melbourne face the challenges of being one of the country’s biggest cities with more than five million residents.
“Building the North East Link is critical to future-proof Melbourne’s road network for the growing population of Victoria,” said Catherine King, Federal Minister for Infrastructure, Transport, Regional Development and Local Government, in a statement announcing the start of Zelda’s journey.
“The start of tunnelling on the North East Link is a major milestone on a project that will get thousands of trucks off local roads,” echoed Victoria Premier Jacinta Allan.
Taking up to 15,000 trucks off local roads every day is one of the benefits of the project. It will reduce CO2 emissions, traffic congestion and travel times by up to 35 minutes. Related works include upgrades to the Eastern Freeway and the M80 Ring Road with new lanes, smart technology and connection to the tunnels.
