Building the West Gate Tunnel

1 March 2022

The West Gate Tunnel Project is building twin tunnels between the Maribyrnong River and the West Gate Freeway, providing a vital alternative to the West Gate Bridge.

The project will ensure quicker and safer journeys and remove over 9000 trucks from streets in the inner west.

The tunnels are being built using two tunnel boring machines (TBMs) so the community and businesses can continue above ground while work happens below.

While the TBM bores up to 27m under the ground, it also installs a concrete lining, forming the walls, roof and base of the tunnel.

The TBM excavates rock and soil with a rotating cutterhead, before moving forward to make space for the concrete lining. It then stops moving and installs the lining using a specialised rotating machine.

Tunnelling requires highly specialised skills. Behind the TBM, crews work to build the road surface and install electrics, ventilation and safety systems.

To inspect the TBM cutterhead, up to 4 workers will enter a pressurised air lock to perform routine maintenance work in compressed air conditions. The compressed air is used to keep the groundwater away from the working area. The physical effects are similar to scuba diving to a depth of up to 35m.

After completing the maintenance tasks, the workers then spend up to 2 hours depressurising before returning to the surface.

The TBMs will excavate around 1.5 million cubic metres of dirt and rock while building the tunnels – enough to fill the MCG.

During tunnelling, excavated dirt and rock is moved from the tunnel face to the rear of the TBMs by a series of internal conveyor belts.

From there, the dirt and rock moves on to a covered conveyer that will transport the excavated material away from the northern portal and over Somerville Road, straight into the massive spoil handling shed at the project’s tunnelling hub.

Once it reaches the shed, the conveyor will empty the excavated material into large bins before it gets loaded onto covered trucks and transported away from site.

Tunnel soil will then be transported to a purpose built disposal site in Bulla.

What to expect

Our TBMs will operate, 24 hours a day, seven days a week and will reach a depth of up to 27m below ground. They have been purpose built to suit local ground conditions so that large-scale construction can happen underground, with minimal disruption above.

TBMs are very good at reducing vibration so many people living and working above the tunnel may not notice construction happening underground. We will:

inspect the properties above the tunnel before and after construction
monitor ground movement and vibration levels at all times
meet strict targets set to manage vibration and minimise disruption.

Man-made fill

The top layer on the surface, which is man made, is used to change the elevation or gradient of the surface and easy to tunnel through.

Strong upper basalt rock

Younger basalt rocks, normally one of the strongest rocks and will need special disc cutters to break through.

Sediments

Soft ground made up of sand and clay soil, much easier to tunnel through than basalt.

Lower basalt rock

Much older rock that has a mix of hard and soft ground types, requires both disc cutters and soft ground tools to excavate through.

People above and 50m either side of the tunnels’ alignment may feel some minor vibration or hear noise that travels up through the ground as the TBMs passes underneath. This is normal and expected for any tunnelling project, but depends on the ground conditions in the area and the property’s foundation construction.

Noise heard within a building that is generated by vibration transmitted through the ground into a structure is typically heard as a low frequency “rumbling”.

Our sophisticated TBMs are very effective at minimising vibration and ground movement. We also utilise a wide range of monitoring equipment, both in and above ground, to review and assess any tunnelling impacts. This allows us to adjust our methods accordingly as we move through a range of ground conditions. It is important for us to measure the effects of tunnelling on nearby buildings, infrastructure, and the ground surface. While the activity is low risk, this real-time monitoring will ensure any mitigation measures can be actioned immediately.

How long will the monitoring equipment be in place for?

Monitoring data is continuously recorded and provided to engineers and the TBM operators.

For the past two years monitoring equipment installed around the Yarraville area and has provided the project with invaluable information about the ground movement behavior during various seasons and events such as an earthquake.

Where monitoring equipment has been installed on buildings, inspections of those devices will be undertaken weekly when the TBMs are within 100m.

The frequency will then increase to daily when each TBM is within 50m either side of a property.

Some monitoring equipment will be in place until tunnelling is complete.

While property damage is very unlikely to occur, properties near the tunnel alignment have previously received an offer for an independent property condition survey prior to tunnelling. These property condition surveys are in place to give peace of mind to owners about existing conditions and ensure any damage can be accurately assessed.

In the event of any damage, claims will be assessed by an independent insurance assessor.The property condition survey and ground monitoring data collected before and during tunnel construction will be used during the assessment.

During tunnel construction if you believe the works have caused damage to your property then you can contact the project on 1800 105 105. or info@wgta.vic.gov.au. A member of our community relations team will then contact you at the earliest convenience.

If you have not had a property condition survey undertaken and would like to do so, please contact us on 1800 105 105.

Once works are completed under your property, a final property inspection will be offered.

The TBMs are expected to bore up to 9m a day, 24 hours a day and 7 days a week. The main tunnelling construction compound at Whitehall Street will be operating both day and night.

Keeping you informed

We will keep people informed and work together to make things easier during construction.

You can expect to see regular information from us about construction activities happening in your area, including:

newsletters to keep you up to date
work notifications in your letterbox
weekly information drop in session with tunnel experts every Wednesday from March between 4.30pm–6.30pm at the Information Centre
information on the website
news and updates on social media.

Our West Gate Tunnel Project Information Centre is also open Monday – Friday from 10am–5pm and Saturday 10am–4pm for project information and enquiries.

The Information Centre is located at the corner of Somerville Road and Whitehall Street, Yarraville.

We also have a team that is dedicated to working with the community. They are available 24 hours a day, seven days a week to answer any questions or concerns.

Download fact sheet

Building the West Gate Tunnel (PDF 1.6 MB)