Metro Tunnel cross passage construction at halfway mark

While the Metro Tunnel Project has said goodbye to its four massive tunnel boring machines – Joan, Meg, Mille and Alice – there’s still some serious digging going on under the city as work on the project continues.

With the nine-kilometre twin rail tunnels now complete, the focus within the tunnels is on the 26 cross passages that will serve as escape routes for staff and passengers in an emergency.

There will be a cross passage about every 230 metres along the tunnels, all the way from Kensington to South Yarra.

While smaller than the rail tunnels they connect, they will still be an impressive size at four metres high – the height of a single-storey house.

At each site crews carry out geotechnical drilling above ground first to check ground conditions. In some places grout is injected into the soil to strengthen it before digging starts underground.

The passages are built by breaking through the walls of the rail tunnels, which are braced with steel, and then excavating between them with equipment including a wall saw and an excavator-mounted jackhammer.

Once mining is complete, the cross passages are reinforced with steel, waterproofed, and lined with concrete before a floor slab is poured.

Construction of each cross passage takes around six months, with work taking place concurrently across different sections of the Metro Tunnel.

As each cross passage is completed, floor slabs are poured in the rail tunnels and fit-out starts with the installation of cable trays, brackets and plumbing.

Fourteen of the cross passages are now complete, with work to dig and fit out the remaining 12 expected to be finished by early next year.

At the same time major progress is being made across the Metro Tunnel Project’s five new underground stations at Arden, Parkville, State Library, Town Hall and Anzac (St Kilda Rd), with the project on track to open to passengers in 2025 •