Three machines known as "roadheaders", each weighing more than 100 tonnes, have been digging deep into the ground for about eight months. Inside the Metro Tunnel. Credit:Luis Enrique Ascui The first stages of the Metro Tunnel's State Library station. Credit:Luis Enrique Ascui Last week, the roadheaders excavating the tunnel from either end met underground, marking a major tunnelling milestone for the project. The State Library is one of five underground Metro Tunnel stations being built by the Andrews government as part of the massive new rail project.

The cavern is set to be finished by late next year, with 20 per cent of it excavated so far. The structure has been built 30 metres underground and needs to be dug about 10 metres further below, while another three access shafts for the station are at earlier stages of excavation. Piling is underway at a third shaft on the corner of La Trobe and Swanston Streets with a roadheader still yet to be launched. A fourth shaft is at the western side of Franklin Street and a fifth on Little La Trobe Street near Literature Lane.

Public Transport Infrastructure Minister Jacinta Allan said a series of access shafts were being built to avoid ripping up Swanston Street and disturbing the city's busiest tram route. "You can see here the size and scope of the works underneath the ground ... it's being done while keeping the tram operations running above ground and keeping the city moving, which has also been a key priority in how we consider the staging and delivery of this big and important project." Rail Projects Victoria's chief executive Evan Tattersall said the station would be dug out gradually, with the first of three levels or "benches" now excavated at the State Library site. "Because it's so big in scale ... you can't do it all in one bite," Mr Tattersall said. The tunnel is set to be finished by late next year, with 20 per cent of it excavated so far. Credit:Luis Enrique Ascui

Loading Replay Replay video Play video Play video "We've got two more levels yet to go beneath us to get down to the base of the excavation. "To the sides of us there are additional tunnels that need to be done with the roadheaders," he said. The station platforms will be built about six metres further underground, Mr Tattersall said. "We are this deep because we need to get under the existing City Loop."

Workers in the Metro Tunnel on Thursday. Credit:Luis Enrique Ascui The tunnels beneath the CBD will be built in a "trinocular" design, meaning there will be three overlapping tunnels built – a complex design required for Melbourne’s challenging geological conditions. Loading During construction, the access shafts will be used to lift road cutters and massive tunnel boring machines in and out of the ground. Some of the access points will eventually form entrances for the tunnel.