Cross passage collapse stops work on Melbourne’s West Gate Tunnel

An underground collapse on a cross passage last week has stopped work on part of the West Gate Tunnel project in Melbourne, Australia.

Workers were excavating a cross passage 25m below ground when rock and soil started to spill into the West Gate Tunnel's inbound tunnel about 1km in from its northern entrance at Yarraville in Melbourne.

The project's twin tunnels – a 4km outbound tunnel and a 2.8km inbound tunnel – run under Yarraville between the West Gate Freeway and the Maribyrnong River. The CPB Contractors and John Holland joint venture (CPBJH JV) completed boring on the twin tunnels last month.

The Australian Workers’ Union confirmed that no one was hurt in the incident, which occurred in the early hours of Friday morning (2 June).

The union's lead construction organiser Joel Archer said that part of the cross passage tunnel, which runs between the twin tunnels, collapsed because of high moisture content in the ground.

Archer said there will be engineering assessments to establish the next steps to make the ground safe.

While work on excavating the cross passages remains paused, work is still continuing in the fit out of the outbound tunnel and road deck construction.

Archer told ABC news: "What has happened is there's been a collapse of the ground as they were excavating. It hasn't resulted in any injury to any worker."

Archer said that it is not uncommon for ground to be unstable due to Melbourne's high water table and its complex geology.

He confirmed that the area was evacuated following the incident and an exclusion zone has set up in the inbound tunnel.

A spokesperson for the West Gate Tunnel Project said: "The soil and rock movement from one cross passage between the two tunnels is now stable and the clean-up continues following this minor incident.

"Work is focused on reinforcing the site before the soil and rock can be removed."

The CFMEU has supplied this vision of the collapse at the West Gate Tunnel project overnight. No one was hurt. @abcmelbourne pic.twitter.com/JeqPbSJYgA

— Margaret Paul (@margaretpaul) June 2, 2023

But the Construction, Forestry, Mining and Energy Union (CFMEU) said that the incident was "concerning".

Speaking to 7NEWS Australia last week, CFMEU Victorian State secretary John Setka said that works should stop "until they have a full investigation to see what happened, what's caused it and to make sure they put counter measures in place to make sure that it never happens again".

A WorkSafe Victoria spokesman confirmed that its inspectors have attended the site and will determine what further action is required.

The multi-billion-dollar West Gate Tunnel is one of the largest diameter bored excavation projects in the world. It is a partnership between the Victorian Government and Transurban to give Melbourne a second freeway link between the west and the city.

The project has faced delays and cost increases due to an issue with contaminated soil between the client and contractors.

Towards the end of 2019, tunnelling preparations were halted as per- and polyfluorinated alkyl substances, chemicals used in firefighting foam, were identified in the soil. This led to a dispute between Transurban and CPBJH JV over which party would be responsible for the cost of the disposal.

The parties ultimately came to an agreement, and tunnelling was able to start in March 2022.

This, however, caused the completion date to be postponed by three years and an increase in the project cost to at least the tune of the D&C contract value increase.

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