Rendering Courtesy of MMRA
Planned $8.1-billion rail tunnels will be excavated under dense urban conditions.

Rail officials have procured half the cost of a planned $8.1-billion tunneling project in Melbourne, Australia, but the 9-kilometer-long tunnel-boring plan, which is slated to begin in 2018, still faces political hurdles.

The Melbourne Metro Rail Authority (MMRA) has opted for tunnel-boring machines to excavate twin tunnels underneath the Yarra River, which poses “a number of engineering challenges, including navigating complex geological and hydrological conditions, the need to protect the environmental significance of the river and limited space on either side of the river for construction,” says MMRA Chief Executive Officer Evan Tattersall.

The plan is the preferred outcome of studies that explored other options, including cofferdams and immersed tubes, which would have involved dredging the riverbed and therefore were considered too disruptive. The project will include five new stations as well as the tunnels. The project is expected to allow 20,000 more passengers to use Melbourne’s rail network during peak hours. Because of its proximity to densely populated brownfield areas, Tattersall likened the project to London’s Crossrail and New York City’s Second Avenue subway.

In June, an Aurecon-Jacobs/Mott MacDonald (AJM) joint venture was appointed the project's technical, planning and engagement adviser. AJM is progressing technical, planning and engagement work, while the MMRA is responsible for overseeing planning works, developing a project reference design, undertaking site investigations, and planning approvals, procurement, construction delivery and project commissioning.

The tunnels will be situated, on average, 10 meters below the surface and sit to the east of the Princes Bridge, which is about 7 m below the riverbed. The details of the final location, design and construction methodology will be determined by the future construction contractor. Extensive geotechnical investigations are currently underway.

When announcing the government’s preferred delivery of the scheme at a press conference, Minister for Public Transport Jacinta Allan stated that $3.3 billion of funding already was secured. However, uncertainties remain about the project’s funding. While federal Infrastructure Minister Warren Truss has said he will not make a decision on funding until he is approached about it, Prime Minister Tony Abbott has insisted repeatedly that the federal government is opposed to funding urban rail projects.