Farewell our mega borer friends


Four giant boring machines are leaving Sydney after finishing tunnelling under the city, delivering 30km of twin metro railway tunnels.

Their massive cutterheads, each weighing 100 tonnes, are being lifted out of construction sites in four military-style operations.

This marks the successful completion of major tunnelling construction under the centre of city and the city’s north on the Sydney Metro City & Southwest project.

Each 1,100 tonne tunnel boring machines (TBMs) tunnelled through sandstone and shale under Sydney at an average rate of 167 metres per week.

Each TBM had 38 teeth-like cutters made from hardened steel. Each cutter weighed 250 kilograms and had to be changed about every 10 days because of the forces of tunnelling. Altogether, each TBM went through about 200 cutters.

TBMs Nancy and Mum Shirl each built 8.1 kilometre tunnels from Marrickville to Barangaroo, passing through new metro stations at Waterloo, Pitt Street and Martin Place.

They started tunnelling in October and November 2018 respectively, and arrived at Barangaroo in December 2019 and January 2020.

TBMs Wendy and Mabel each built 6.1 kilometre tunnels from Chatswood to Blues Point, passing through new metro stations at Crows Nest and Victoria Cross.

They started tunnelling in January 2019 and February 2019, arriving at Blues Point in November 2019 and December 2019.

A330-tonne tower crane extracted TBMs Nancy and Mum Shirl from Barangaroo as they were disassembled and returned to the manufacturer.

The TBM tunnelling under Sydney Harbour, Kathleen, is currently completing the second metro railway tunnel under the harbour.

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