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Metro Tunnel

What's underneath Melbourne


[Title: What's Underneath Melbourne]

Liz Mooney – Geotechnical Engineer

The site investigations for Melbourne Metro are taking place alignment-wide, so from South Kensington, right through the CBD and then through to South Yarra.

[Vision: Animated map of the Metro Tunnel's alignment, highlighting Kensington, Arden, Parkville, CBD North, CBD South, Domain and South Yarra]

Chris Mitchell – Senior Project Engineer

The overall reason for doing site investigations is essentially to understand what's underneath Melbourne.

[Vision: Construction workers at a Metro Tunnel geotechnical investigations site]

We need that information to help us design the stations, the tunnels – essentially where they'll go and how it is that we can construct them.

[Liz Mooney speaking]

There are many types of site investigations that we're performing for this project. One of the key investigations is geotechnical drilling.

[Vision: Workers drilling a hole into the ground and collecting soil from it]

The reason we do that is so you can understand what underlies the ground and recover soil and rock samples that are critical to the design of the stations and the tunnels.

[Vision: Shot of a "danger" sign indicating buried pipelines. Cut to Metro Tunnel workers scanning the ground and looking at maps]

The typical process is that we first need to come in and scan and locate underground services. That's a key part of the process in order to protect key assets under the ground.

[Chris Mitchell speaking]

Once we've found the location that's clear of services, we bring the drilling rig in.

[Vision: Construction workers spray painting the ground. Cut to shot of a fenced off site with drilling equipment]

We set up over the location and then we essentially start drilling down into the rock and we retrieve samples of the rock down to approximately 50 metre's depth.

[Liz Mooney speaking]

We found various types of rock conditions throughout the alignment. It varies from hard basalts, through to softer siltstones and mudstones.

[Vision: Construction workers inspecting samples]

[Chris Mitchell speaking]

And we're really trying to target the interface where those different materials meet, so we can define a 3-D picture of what's underneath Melbourne.

[Vision: Animation showing Princes Bridge and a cross section of the Yarra River. An animated barge drills down into the river. Cut to workers in a survey boat driving down the river]

[Liz Mooney speaking]

In the Yarra River, we've done various investigations. We had a barge on the river for a couple of months that was drilling boreholes. We've also done a survey of the surface of the sedimentary material underlying the water.

[Vision: Technical map of the Yarra River and infographic about station depths]

[Chris Mitchell speaking]

It's important to do these investigations under the Yarra River so we have confidence of exactly what we're going to find when we do bring our Tunnel Boring Machines in under the Yarra River, as it's quite a complex environment.

[Vision: Pedestrians crossing a bridge over the Yarra River]

It's a real privilege to be able to work on this kind of project as an engineer, and just face all the challenges that these kinds of projects around the world really have to face. And it's great to be able to do this an environment like Melbourne.

[Vision: Time lapse view of CBD skyline, overlooking the Yarra River]

[Liz Mooney speaking]

We're leaving a legacy for Melbourne. It's not often that a project of this scale happens in your home city, so it's very exciting to work on.