Sydney Metro finishes city centre tunnels

22 January 2020


Australia – Four out of five drives for the Sydney Metro’s ‘City and Southwest’ phase have been completed. The most recent breakthrough was into Barangaroo Station. These drives represent the entirety of the city centre tunnels, with only a second tube crossing the harbour still to be completed. As of 21 January, some 97% of tunnel excavation had been completed.

The completed 15km of twin tunnel were excavated by contractor John Holland-CPB-Ghella using 7.01m-diameter Herrenknecht Double Shields through sandstone and shale. The harbour crossing TBM still working is a 7.04m Herrenknecht Mixshield.

The sandstone tunnels house a six-segment rhomboid and trapezoidal lining. Each segment is 1.7m long, 260mm thick and weighs about 3.75t. The thickness is so the segments can tolerate the push of the TBMs thrust rams, for situations where the TBM is not just pushing off the grippers.

The lining under the harbour crossing is 280mm thick for increased ground support and also incorporates a keystone, for seven segments in total. This is because higher loads on the under-harbour sections required straight edges for the segments and so a traditional segment design with a keystone was selected.

Predominantly the segments are reinforced with Dramix steel fibres from Bekaert Maccaferri, but conventional rebar from the Australian Reinforcing Company is used for cross passages and might be considered if unusual geology is encountered. All of the segments incorporate cast-in Datwyler gaskets and fireproofing is with poly fibres from Propex.

The reference design was undertaken by WSP Parsons Brinkerhof, Aecom, Cox, Hassall. The detailed designers were Hochtief Engineering, Noma Consulting, Pells Sullivan Meynink, McMillan Jacobs, Arcadis BG&E.

For more information, please see the feature in Tunnels and Tunnelling International, January 2020, pp.20-27

The City & Southwest alignment