Sydney Metro Project: history made as metro tunnelling complete under Sydney Harbour

New twin metro railway tunnels deep under Sydney Harbour are complete in a historic milestone – with all tunnelling now finished on the Sydney Metro City & Southwest project.

Mega boring machine Kathleen has arrived north of the harbour, where she broke through a wall of sandstone in a spectacular arrival.

TBM Kathleen dug two 885-meter tunnels from Barangaroo to Blues Point.

It took two months to build the second tunnel – one month faster than the first, due to lessons learned like modifying the giant cutter head and changing tunnelling processes to better deal with the clay material at the bottom of the harbour.

The five TBMs on this project have delivered 31 kilometers of fully lined tunnels in only 17 months.

TBM Kathleen dug through about 175,000 tons of sandstone, clay and marine sediments to build both harbour tunnels, which are about 40 meters below sea level at their deepest point.

Kathleen and her crew of 50 have delivered a world-class piece of infrastructure almost a century after her namesake helped build the Sydney Harbour Bridge above them. The specialized TBM is named after Kathleen Butler, who played a vital role in the construction of the Sydney Harbour Bridge as the technical advisor to legendary engineer John JC Bradfield.