Sydney Metro City & Southwest

Australia

Sydney Metro is the most imposing infrastructural project in all of Australia, and it involves the development and the building of the Sydney metro network.

Ghella was commissioned to build the “Sydney Metro City & Southwest” section, which comprises 15.5 kilometres of new twin tunnels and the execution of civil works for the construction of six new stations: Waterloo and the new underground platforms of Central Station, Pitt Street, Martin Place, Barangaroo, Victoria Cross (North Sydney), and Crows Nest.

What is unique about the new tunnels in the project is that they connect to the overhead infrastructure that exists in the areas of Chatswood and Marrickville, after which they travel below Sydney Harbour and some highly urbanized areas like the City Business District. The excavation of the stations of Pitt Street and Martin Place came about in the most populated and congested area of Sydney.

Once the stretch is completed, it is estimated that the capacity of the metro will increase from about 24,000 to 40,000 passengers per hour, and that the trains will have an average frequency of one train every two minutes.

Tunnel Boring Machines (TBMs) were used to excavate the tunnel. These are machines that are capable of excavating tunnels in a completely mechanized way and in total safety. TBMs, commonly known as “moles”, excavate the rock with a rotating cutting wheel equipped with cutters. They remove the excavated material and line the tunnel that was just made by installing prefabricated segments. To excavate underneath the city four double-shield TBMs were chosen, 6.93 metres in diameter each, while a 7.05-metre Hydro TBM was used to excavate under the harbour.

In line with tradition, the moles were given the names of women. In this case, the names chosen are those of especially important Australian women: Nancy, in honour of Nancy Bird-Walton OBE, Australian aviator and founder of the Australian Women Pilots’ Association; Mum Shirl, Aborigine woman and activist, who dedicated all her life to the defence of the rights of Australian Aborigines; Wendy, after Wendy Schreiber, volunteer in the only refuge for children with disabilities in New South Wales; Mabel, in honour of Mabel Newill, head nurse at the Royal Prince Alfred Hospital of Sydney; and lastly Kathleen, after Kathleen Butler, the only technical consultant of John Bradfield, the engineer who designed the bridge crossing Sydney Harbour. The first woman in Australia to fill such a prestigious position, she played a key role in the construction of the bridge.

Sydney Metro City & Southwest has already left its mark on the history of great infrastructures: indeed, it is the first time that a railway tunnel has been excavated under Sydney Harbour, and the excavation was particularly complex owing to the marine deposits and the geological conditions of the clayey seabed. On the remainder of the stretch the excavated rock was prevalently Sydney Sandstone, a sandstone rock that is stable and not too abrasive. In the site of Barangaroo, where it took two years to excavate over 460,000 tonnes of rock, a ship from 180 years ago was discovered, the first ship built in Australia ever to be found in the region.

Owing to its technical difficulties, to the innovative sustainable project design, and to the revolutionary impact that it will have on urban mobility in the city of Sydney, the project is destined to be one of the most significant in the framework of the infrastructural development plans begun in New South Wales.

Excavation with the TBMs was completed in the early months of 2020, in just 17 months, and three weeks ahead of schedule. The staff included over 560 technicians and engineers, and over 1,800 workers, for a total of more than 10 million work hours.

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