Overview

Along its route, the depth of the Metro Tunnel is up to 40m. The deepest point is under Swanston Street, at the northern edge of the CBD, where the new tunnels pass under the existing City Loop tunnels.

Building the Metro Tunnel presents many challenges, including:

• managing disruption to residents, businesses and public events
• minimising potential impacts on road traffic, pedestrians, cyclists and existing public transport and freight services
• navigating existing underground infrastructure – including the City Loop, CityLink tunnels and services such as water, gas and electricity
• excavating through a range of challenging geological conditions including rock, sands, clays and silt
• tunnelling under 2 significant waterways, the Yarra River and Moonee Ponds Creek
• managing the removal and disposal of large amounts of excavated material.

Hundreds of geotechnical site investigations developed our understanding of existing geological conditions across the alignment and confirmed the location of underground services. This information has also informed the construction methodology for building different elements of the project.

Around 1.8 million cubic metres of excavated soil and rock was produced during the construction of the Metro Tunnel. As the bulk of works are underground, there are limited opportunities to re-use excavated clean fill as part of construction. As such, it needed to be removed from construction worksites before it can be re-used at other locations. Materials that could not be re-used due to contamination were disposed of in line with Environment Protection Authority (EPA) Victoria and WorkSafe Victoria guidelines.

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