The milestone on the Australian project was marked with the arrival at her final destination of tunnel boring machine (TBM) Kathleen. She broke through a wall of sandstone, meaning that the twin metro railway tunnels deep under Sydney Harbour are now both complete in a historic milestone.
TBM Kathleen dug two 885m-long tunnels from Barangaroo to Blues Point.
It took two months to build the second tunnel – one month faster than the first, thanks to lessons learned such as 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 the project have delivered 31km 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 40m below sea level at their deepest point.
Kathleen and her crew of 50 have delivered the 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 engineer John JC Bradfield.