Diverting a 100 year-old sewer

Before tunnelling can begin, we needed to divert a 600m section of the North Yarra Main Sewer.

Completed in 2019, the diversion works was a massive job that involved excavation, piling, boring and temporary changes to traffic and we built it without interruption to sewerage services.

About the North Yarra Main Sewer

The original North Yarra Main Sewer was 2.6m in diameter, over 100 years old and made mostly of bricks. It’s a vital piece of infrastructure that sits 13 to 15m below the ground and carries 20% of Melbourne’s sewage.

As part of the project, a 600m section of sewer that ran below the centre of Whitehall Street in Footscray and Yarraville was diverted. This was done to protect the sewer from tunnelling and prevent disruptions to sewer services across Melbourne’s north and west.

About Mollie - our mini tunnel boring machine

To keep the old sewer operating all the times, a mini TBM called Mollie created a route for the new sewer. As the mini TBM moved through the earth at the rate of about 12m a day, glass-reinforced plastic lining was installed around the tunnels to seal and strengthen the structure.

Once the new sewer was ready to operate, a gap was opened in the wall of the old sewer so sewage could start flowing via the new tunnel.

Over 9000 cubic metres (3.6 Olympic size swimming pools) was excavated during the diversion works.

See the moment Mollie broke through

We caught the West Gate Tunnel Project's first TBM breakthrough on film - watch the video to find out more about Mollie and diverting the North Yarra Main Sewer.