Tunnelling under the Yarra River
The Metro Tunnel will be constructed under the Yarra River, which is up to four metres deep in this location. The top of the twin tunnels, each around seven metres in diameter, will be approximately 12 metres below the riverbed, east of the Princes Bridge.
Crossing under the Yarra River is a significant element of the project and presents a number of engineering challenges, including:
- complex geological and hydrological conditions, and
- safeguarding the environmental significance of the river,
- limited space on either side of the river for construction.
Tunnelling using tunnel boring machines has been selected as the preferred method of construction of this section of the project.
Ground conditions under the Yarra River are very complex, with geotechnical investigations showing different soil types including basalts, silts and clay. More than 20 geotechnical bore holes have previously been drilled in this location to inform decision-making. In 2016 we undertook a second stage of drilling to supplement these results.
Additional geotechnical investigations have also been undertaken in 2018 to better understand the complex geological nature of the Yarra Crossing.
Working with local businesses and traders
We are committed to working closely with local Yarra River businesses, traders and sporting clubs to manage and minimise the unavoidable impacts of construction. We will undertake ongoing consultation to understand their needs and how these might inform the planning and delivery of the project.
We will work closely with Parks Victoria, Heritage Victoria, the Department of Environment, Land, Water and Planning, and the Environment Protection Authority Victoria to identify measures to minimise impacts on the Yarra River, aquatic and plant life, and the surrounding area.