The Victorian Government has ordered four tunnel boring machines (TBMs) to burrow the nine kilometre twin tunnels for the Metro Tunnel Project.
The TBMs will start arriving in early 2019 to build the $11 billion Metro Tunnel that will transform Melbourne’s transport network.
Each TBM will be 100m long, weighing up to 1000 tonnes and a diameter of 7.2m.
They will operate like moving factories as they travel beneath the city’s surface, with giant cutting heads burrowing through soil and rock before its transported via pipes to the surface.
The custom-built machines include offices, kitchens and bathrooms to support crews of up to 14 people during a round the clock operation.
They will progressively install watertight concrete lining as they move under the surface at around 10m a day building the new tunnels.
The heaviest single component of each TBM is the cutterhead, which weighs in at 175 tonnes and can tunnel through rock six times harder than concrete.
The deepest tunnelling point will be under Swanston Street, at the northern edge of the CBD near the new State Library Station. Here the TBMs will excavate around 40m below the surface.
The four TBMs will install a total of 55,000 individual concrete segments that are needed to create the two tunnels.
Victorian Minister for Public Transport, Jacinta Allan, said, “These machines will operate like giant underground factories as they burrow around 40m beneath Melbourne to build the Metro Tunnel.
“They will dig through a variety of ground conditions to link one side of the city to the other and its completion will represent a significant engineering feat.”
Upon their arrival, two machines will be transported to Arden and two to Domain, where they will be assembled, lowered into a shaft 20m underground and launched into the earth.
Each TBM will head away from the city on the first leg of their journey before being retrieved in Kensington and South Yarra.
They will then be retrieved, dismantled and trucked back to their starting points to be re-launched towards the city, with tunnelling expected to be complete by 2021.
Significant work has already been undertaken at both launch sites to prepare the areas for tunnelling work, including the installation of temporary construction power substations to power the TBMs from both locations.
The Metro Tunnel will create a new end-to-end rail line from Sunbury to Cranbourne/Pakenham and five new underground stations, allowing more frequent, reliable trains to run between the city and suburbs each day.