Melbourne is the nation’s fastest growing capital city and is on-track to overtake Sydney as Australia’s largest within 40 years. While population growth might not be inherently problematic on its own, it does bring a range of challenges, notably stress to city infrastructure and road networks.
The Victorian government, in partnership with Transurban, is attempting to mitigate these challenges with the West Gate Tunnel (WGT) project.
The state government WGT project summary highlights Melbourne’s west as one of the city’s fastest growing regions. According to the summary, this is due to a combination of land use changes, urban renewal in the inner suburbs, and residential development in the outer suburbs.
Melbourne drivers will likely attest this growth is being felt on the West Gate Bridge, which is nearing capacity and sees up to 220,000 vehicles each day. The project summary estimates this will grow to 270,000 by 2031.
Additionally, the summary notes Melbourne’s role as a national import and export logistics hub as a driving force behind the WGT concept.
“Container trade through the port of Melbourne is forecast to grow steeply, reaching eight million standard containers a year by 2035 – 3.5 times the current level,” the summary indicates.
“Growing freight activity is increasing demand for the movement of goods on the city’s freeways, changing preferred access routes to and from the Port of Melbourne and leading to additional heavy freight traffic moving from the port through the inner west.”
The WGT intends to shift Melbourne’s reliance on the West Gate Bridge and facilitate new connections to the city. Roads and Infrastructure Magazine explores how.
The WGT construction contract was awarded to a joint venture between CPB Contractors and John Holland in 2017. The project’s engineering and design contract was awarded to a Aurecon and Jacobs Joint Venture (AJJV) in 2018.
AJJV was awarded the contract after developing a concept for the project, involving extensive stakeholder and community engagement and technical investigations to enhance the initial proposal.
Design Director, Mark Percival, says the West Gate Tunnel will provide a second Yarra River crossing and alternative route to the West Gate Bridge, improving the local amenity of the region and upgrading connectivity from the city to the developing western suburbs.
According to Mr. Percival, the project will improve connections between Melbourne’s west, the city centre and it’s major ports.
“Jobs like this are few and far between, and a single consultancy would struggle to mobilise a large enough team to deliver detailed design during the peak delivery period. Jacobs and Aurecon are culturally aligned companies and we have worked together successfully in the past,” says Mr. Percival.
“The complexity and size of the project relies on a collaborative team effort, which cannot be achieved without setting the right culture from day one.”
Mr. Percival says public and media attention on the WGT has centred largely on the tunnel itself, with many unaware the project encompasses three distinct work zones – surface works to the west, twin bored tunnels and 20 kilometres of elevated road structure in the east.
“In addition to the tunnel itself, our design includes four additional lanes on the West Gate Freeway, as well as ramps between the West Gate Freeway and Hyde Street for local trucks. Then there is a tunnel under Yarraville that connects the West Gate Freeway with the Maribyrnong River, new bridges over the Maribyrnong River, as well as a 2.5 kilometre veloway and 14 kilometres of upgraded cycling and walking paths,” says Mr. Percival.
The twin tunnels under Yarraville will measure four kilometres outbound and 2.8 kilometres inbound.
WGT Authority Communications Deputy Director, Kim Payne, estimates the project will remove up to 9,300 trucks from local roads in the inner west each day.
“With a direct route to the port, trucks will no longer have to rely on residential streets, which will protect residential areas from the impact of the forecast growth in the metropolitan freight task,” Ms. Payne says.
The Victorian government has announced it will enforce a 24-hour truck ban in the inner west, following project completion.
Ms. Payne says traffic modelling carried out for the WGT Environment Effects Statement showed the project would save motorists up to 20 minutes in travel time from the west and 13 minutes to the Port of Melbourne.
“The modelling also showed that by offering an alternative to the West Gate Bridge, more than 8,000 trucks are diverted away from the bridge each day.”
To minimise traffic disruptions, Ms. Payne says the WGT Authority will attempt to keep all lanes open on major roads during peak periods, organise traffic works to happen at night and provide clearly signposted detours where required.
“Additionally, we will work with VicRoads, local councils, Bicycle Network Victoria and other key stakeholders to implement traffic changes.”
West Gate Freeway Widening
According to Ms. Payne, there are currently 3,500 people working on the WGT in fields ranging from construction, engineering, design, environmental management and community relations.
“Over the course of the project there are expected to be over 500 jobs for apprentices, trainees and graduates. About 400 jobs will be dedicated to residents of Melbourne’s west and 150 jobs for people affected by closures in the manufacturing industry,” Ms. Payne says.
“At the peak of tunnelling, 500 people will be working at sites in Footscray and Yarraville, which will be the hub of tunnelling activity.”
Construction on the project’s West Gate Freeway Widening section began in 2018 and is scheduled to continue until 2022.
“Works are well underway to widen the West Gate Freeway by creating an additional four new through lanes.
“This will result in a total of 12 through lanes, plus additional auxiliary lanes,” Ms. Payne says.
“New electricity monopoles were recently installed, replacing two of the lattice towers. These new monopoles will take up less space, allowing the extra lanes to be built.”
According to Ms. Payne, work is also underway diverting a large sewer line that runs under the West Gate Freeway at the Williamstown Road interchange.
These works will facilitate access once tunnel boring machines reach the space next year.
“Works are also progressing on the Millers Road area of the West Gate Tunnel project. Recent achievements include completion of piling and retaining walls under the West Gate Freeway on both sides of Millers Road, installation of temporary noise walls along the West Gate Freeway and trenching along Paringa Road to underground additional power lines,” Ms. Payne says.
“Further east of the project, residents will begin to see more activity around Footscray Road, as piling rigs move in to prepare to build the elevated road that will connect the tunnel to CityLink and the city.”
Ms. Payne says piling will soon start in the Maribyrnong River area to prepare for the construction of a new bridge over the Maribyrnong River.
In the coming months, two large-scale tunnel boring machines (TBM) will be launched at the WGT’s northern portal site in Footscray, so tunnelling can begin south west towards the West Gate Freeway.
The WGT’s TBMs are the largest in the southern hemisphere, standing at 15.6 metres in diameter, 90 metres long and weighing an estimated 4,000 tonnes each.
The first of the two TBMs, Bella, arrived from China in December 2018.
The machine took 12 months to build and was tested in China before being disassembled and shipped to Melbourne.
Reassembling Bella took a team of 30 people working 24/7 for 75,000 hours. Additionally, 250-tonne and 500-tonne gantry cranes were required to complete construction. The second TBM, Vida, recently arrived in Melbourne and will soon begin the process of reassembly.
The cutter head of both TBMs exerts a rotation force of 85,000 kilonewtons (kN) per metre.
“The TBM’s will bore up to 40 metres under the ground at the deepest point, the bottom of the tunnel, while also installing a concrete lining, forming the walls, roof and base of the tunnel,” Ms. Payne says.
Bella and Vida will excavate rock and soil with a rotating cutter head, before moving forward to make space for the concrete lining.
Ms. Payne says the TBMs will then stop moving and install lining using a specialised rotating machine.
“TBMs of this size need 10 megawatts of power per machine. A new substation has been built on site at the northern portal, to ensure enough power is supplied to keep the machines moving 24 hours per day, seven days a week,” says Ms. Payne.
“Highly specialised crews will operate the TBMs and behind them crews work to build the road surface and install electrics, ventilation and safety systems.”
According to Ms. Payne, the WGT Authority has recently achieved two project milestones – completing construction on the rock and soil handling shed, and finalising works on the TBM launch site and portal.
The rock and soil handling shed was designed to keep noise and dust at a minimum for nearby residents and businesses, while construction excavates 1.5 million cubic metres of rock and soil to build the central tunnel.
Ms. Payne says over 12,000 work hours went into building the 180-metre-long and 90-metre-wide structure.
“Rock and soil will be taken from underground on the conveyor to the launch site, over the top of Somerville Road on a covered conveyor and then into giant bins before being trucked away,” according to Ms. Payne.
The second project milestone is the Footscray launch site. Coming in at over 300 metres long, 40 metres wide and 22 metres deep, it is roughly two times the length of an AFL oval.
The Footscray portal was built using a cut and cover method. This involves excavating a trench, before covering it with a concrete deck to form a roof.
In the coming months, two TBMs will be launched at the northern portal site in Footscray and start tunnelling south west towards the West Gate Freeway.
“The TBMs are expected to bore nine metres a day, 24 hours a day, seven days a week,” says Ms. Payne.
“Work will start on the four-kilometre outbound tunnel first, closely followed by the 2.8-kilometre inbound tunnel. The longer tunnel will take an estimated 18 months to excavate.”
In the 18 months since work started, 6.3 million work hours have been clocked up. Ms. Payne says the project is on track and still scheduled for completion in 2022.