Melbourne Metro Rail: Monster tunnel boring machines could be abandoned underground

MONSTER-sized tunnel boring machines as long as a soccer pitch used to build the Melbourne Metro Rail Tunnel could be abandoned deep under the city.

MONSTER-sized tunnel boring machines as long as a soccer pitch used to build the Melbourne Metro Rail Tunnel could literally dig their own graves.

The Melbourne Metro Rail Authority says it will be up to the successful bidder to decide whether the giant machines used to build the twin 9km cross-city tunnels are abandoned underground once drilling work is complete.

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Two of the 11 tunnel boring machines used to dig the Channel Tunnel between England and France were driven steeply downwards and left there once the 50km tunnel was created.

Melbourne Metro Rail Authority spokesman Reid Sexton said it was anticipated the mega machines would be dismantled underground and their reusable components retrieved.

But Mr Sexton could not rule out that some of the giant earth movers would be parked permanently underground - if it proved cheaper.

A tunnel boring machine in operation in Sydney.

One of the giant machines boring a rail tunnel from Sydney’s Bella Vista to Cherrybrook.

How the giant tunnel boring machines work.

Abandoning the machines, which cost about $20m, may prove more efficient and cost effective for project contractors than hauling them out of the ground.

“Up to six tunnel boring machines will be used during construction, each up to 100 metres long and weighing more than 1000 tonnes,” Mr Sexton said.

“These giant machines are a critical part of the Metro Tunnel project, which will create more services more often to and from the suburbs”.

The $10.9 billion Melbourne Metro contract includes the excavation and fitout of twin nine-kilometre tunnels and five new stations at Arden, Parkville, CBD North, CBD South and Domain.

Up to six tunnel boring machines, or moles, will construct the tunnels outside the CBD and under the Yarra River with smaller machines called roadheaders used under Swanston St.

The mightier machines will be launched near the future Domain station and Arden St precinct.

As part of the works the South African Soldiers Memorial in South Melbourne will need to be temporarily moved.

An artist impression of station CBD South.

Melbourne Metro rail map.

A giant Bunnings style shed will cover City Square for the next five years.

Tunnel boring machines move about 10 metres per day and can operate all day long.

A rotating cutter head churns through the ground with a conveyor belt or pipe carrying the excavated rock and soil to the back.

Vehicles and conveyor belts transport the extracted material- enough to fill 800 Olympic-sized swimming pools - from the tunnel.

Three consortiums have been short-listed to design and build Melbourne Metro.

Two consortiums include companies set to build the East West Link before the Andrews Government scrapped the plan.

Bids for the $6 billion contract are due by April 6.

@AndyJeffo