Before tunnelling for the West Gate Tunnel Project begins in 2019, we need to divert a 600 metre section of the North Yarra Main Sewer. Diverting a sewer is a massive job that involves excavation, piling, tunnel boring and changes to traffic – and we’re going to build it without interruption to sewerage services during the diversion works.

Latest update: Mission complete!

The North Yarra Main Sewer has successfully been diverted and traffic on Whitehall Street, Yarraville has returned to normal after Mollie the mini tunnel boring machine (TBM) finished digging a new sewer line.

Here's what Mollie achieved:

  • 35 days of digging
  • 424 metres of tunnel boring under Yarraville
  • 3,174 cubic metres of dirt excavated

About the North Yarra Main Sewer

The original North Yarra Main Sewer is 2.6m in diameter, over 100 years old and made mostly of bricks.

The sewer runs below the centre of Whitehall Street in Footscray and Yarraville, and it carries 20% of Melbourne’s sewage.

About Mollie

To keep the old sewer operating all the time, a mini tunnel boring machine (TBM) called Mollie was used to create a route for the new sewer. As the mini TBM moved through the earth at the rate of about 12 metres a day, glass reinforced plastic lining was installed around the tunnels to seal it 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 9,000 cubic metres (3.6 Olympic size swimming pools) was estimated to have been excavated as part of this work.

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.

Program of works for North Yarra Main Sewer diversion. Click image to enlarge.

More information

For more details, see the North Yarra Main Sewer diversion factsheet (PDF, 3 MB).

If you have any questions, our team is available 24 hours a day on 1800 105 105.

See upcoming travel disruptions and recent construction notifications.

Find out why we needed to divert the North Yarra Main Sewer