The caverns for the Martin Place metro station illustrate the scale of Australia's largest transport project which,by 2024,will carry tens of thousands of passengers every hour on driverless,single-deck trains.
Each cavern is about 17 metres high and 14m wide,and will eventually feature 160m-long platforms at which trains will pull up at every four minutes.
Similar construction is under way for the three other underground stations in the CBD at Central Station,Pitt Street near Town Hall,and Barangaroo.
The excavation of the caverns at the stations need to be completed before two giant boring machines,worming their way from the city's south,reach the CBD later this year.
Construction of the metro line beneath the CBD is in contrast to thetroubled $2.1 billion light rail line, which has faced long construction delays along George Street in plain sight of Sydneysiders.