Tunnel boring machine (TBM) Kathleen arrived north of the harbour on March 18, breaking through a wall of sandstone.

The TBM dug two 885m-long tunnels from Barangaroo to Blues Point. The second tunnel was completed in two months, a month faster than the first due to the lessons learned such as modifying the cutter head and changing tunnelling processes to better deal with the clay material at the bottom of the harbour.

TBM Kathleen dug through about 175,000 tonnes of sandstone, clay and marine sediments for the two harbour tunnels, which are about 40m below sea level at their deepest point.

Five TBMs working on the project completed 31km of fully lined tunnels in 17 months.

When completed in 2024, the Sydney City and Southwest metro line will be integrated as a single line with the Tallawong - Chatswood Northwest metro line, which opened in May 2019.

The extension includes a 15km greenfield line with seven new stations, along with the upgrade of the existing suburban line to metro standards, covering an additional 13km of track and 11 existing stations. The project also includes expansion of the current Sydney Metro Trains Facility at Rouse Hill and a new depot at Sydenham.

The line will connect with the planned Sydney Metro West that will link the city centres of Parramatta and Sydney.

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