Vida will dig the 2.8km inbound tunnel, taking 12 months to complete the journey.

In March, the first of the two EPBMs, Bella, started work on the 4km outbound tunnel.

Bella and Vida are the largest TBMs in the Southern Hemisphere – each with a 15.6m diameter, 90m long and weighing 4,000 tonnes. They will each dig an average of 9m a day.

The tunnel will be lined with a precast segmental lining in a 10 + 0 configuration, held together by 20 circumferential bolts. The lining has an internal diameter of 14.1m and is 500mm thick with a 40mm universal taper.

The segments are 2.4m long, which are claimed to be the longest segments in the world.

The West Gate Tunnel, due to open in late 2025, is designed to ease congestion on the West Gate Freeway and West Gate Bridge, and reduce the number of trucks on residential streets.

The project is a public private partnership (PPP) between the Victorian government and Transurban, a toll road operator. CPB Contractors and John Holland Joint Venture (CPBJH JV) was awarded the design and construction contract and Aurecon and Jacobs carried out the design work.