Three roadheaders have met 30 metres underground in the first major breakthrough for the Metro Tunnel, connecting two excavated caverns that will become State Library Station.
More than 20 per cent of State Library Station has been dug out so far, to form station caverns and underground passenger connections under Swanston Street.
Over half a million tonnes of material will be excavated, with 1,500 tonnes of rock and soil removed every 24 hours. Excavation is expected to be finished by late-2020.
Seven roadheaders will be used in the CBD in total – four for State Library Station and three for Town Hall Station. Each weighs 118-tonnes, is 15-metres long and is lowered underground in separate pieces, before being re-assembled underground.