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Metro Tunnel

Tunnelling underground


[Title: Tunnelling underground]

[Vision: alignment animation]

Nadine Makin – Design Manager:

We're building a rail tunnel. It will have five stations and be about nine kilometres of rail tunnel.

[Vision: aerial view of Melbourne, showing alignment animation of CBD North]

Paul Thomas – Senior Project Manager, Tunnels and Station Infrastructure:

The reason for the tunnelling is mainly because we are in quite a heavily urbanised area and tunnelling avoids disruption to the roads and the service infrastructure.

[Vision: Animation of TBM digging and creating tunnel under Yarra River. Close up of the cutter head]

A TBM or a Tunnel Boring Machine is designed to respond to the geotechnical conditions that are below the ground for the tunnelling.

Whether it's rock, whether its soil, what the groundwater conditions are, where the groundwater table is, is the rock very hard, is the grown very soft.

Nadine Makin – Design Manager:

Typically, there are two ways of launching a Tunnel Boring Machine: either through a portal or through a shaft.

[Vision: time-lapse of crane lifting a TBM segment into a shaft.]

For this project we're planning to use shafts and so you excavate a large shaft then you lower the TBM in in segments and assemble it underground to form the full machine.

Paul Thomas – Senior Project Manager, Tunnels and Station Infrastructure:

We anticipate that anywhere between four to six tunnel boring machines will be used.

[Close ups of segments being lifted in the air]

There's two components to any Tunnel Boring Machine. There's what we call the shield, which is generally about 15 meters long and that comprises of the cutter head and the motors that run the TBM.

[Vision: unveiling the inside of a Crossrail TBM, close up of rotating cutter head]

These can weigh up to about a thousand tonnes.

[Vision: animation unveiling a TBM's back up system. Vision: Time lapse of a real life TBM moving towards the camera]

Behind the TBM is what we call the gantry system or the backup system. This comprises of individual steel gantries, which will pull behind the TBM and they can be up to eighty to a hundred metres in length.

Nadine Makin – Design Manager:

When you're inside a TBM, it broadly feels like you're in a factory, I think. That's the way I often describe it.

[Animation: zooming in to a TBM's control room]

It is a very controlled environment. Every person has their particular role.

[Vision: Animated TBM removing spoil via conveyor belts. TBM installing concrete segments]

Paul Thomas – Senior Project Manager, Tunnels and Station Infrastructure:

Once the machine has excavated what we call an "advance" - a typical advance could be anything from 1.4 to 1.8 metres - the Tunnel Boring Machine then stops its excavation and behind that, a precast concrete ring is installed to make sure that the ground support is maintained.

Nadine Makin – Design Manager:

The TBM moves away and you've got this lovely concrete ring, which keeps the ground up and will be your final tunnel where your trains will go.

[Vision: Animated close up of concrete rings forming a tunnel. Cross section of the tunnel shows train on tracks, moving towards the camera. Cross fade to London skyline.]

Paul Thomas – Senior Project Manager, Tunnels and Station Infrastructure:

The tunnel boring machines that we will use for Melbourne Metro are no different to what's been used in other projects such as Crossrail in London and Sydney, in Sydney Metro.

[Vision: Camera pans down and zooms into the ground, revealing construction workers working in a tunnel. Fade to Crossrail TBM animation and network map. Fade to animation of Melbourne. Animation of TBM tunnelling under the Yarra river]

These machines are used all over the world. I've used these machines in Hong Kong, Singapore and India, but each is designed specifically for the conditions that are expected.

Nadine Makin – Design Manager:

In cities like Singapore there is almost constantly a rail project being constructed. It's part of the fabric of their city.

[Vision: People walking up Flinders Street Station steps, Myki Gates at Melbourne central. Train timetable screens, and time lapse outside Flinders Street Station at twilight]

Being an engineer you know you need to keep progressing and building projects like this for your city to stay alive and thriving. And it becomes just another element of the life of the city.