Sydney Metro City & Southwest is the second stage of Sydney Metro – the first driverless metro system in Australia. It will deliver 30 km of new metro rail between Chatswood and Bankstown, including new twin tunnels under Sydney Harbour and upgrade and conversion of all 11 stations between Sydenham and Bankstown to metro railway standards. The project will also see new stations at Crows Nest, Victoria Cross, Barangaroo, Martin Place, Pitt Street and Waterloo along with new underground platforms at Central Station.

The project provides a faster, more reliable service for customers by increasing train numbers 60 per cent during peak periods and catering for an extra 100,000 commuters per hour.

Transport for NSW engaged WSP as their technical advisor in 2014. The team worked collaboratively to provide the engineering, rail infrastructure and architectural design support to develop the reference design, tender documentation and final business case for the preferred alignment and station arrangements.

Together, the multidisciplinary team resolved complex issues, including tunnelling methodologies and geology, station depths and arrangements, interfaces and interchanges with the existing transport network – particularly in the dense North Shore and CBD environments. We provided robust input to the options process, including alignment development, station arrangement and connectivity design, constraints mapping and risk assessment.

Geological modelling

We undertook geological modelling to inform the scope and reference design. WSP undertook site investigations, conducting geophysical testing and a suite of marine borehole investigations. This included the following surveys: echo sounding/bathmetric to provide a map of seabed levels; side scan sonar to map seabed features; seismic reflection to profiling to map the subsurface velocity distribution, confirming the depth of rock and identifying any significant variations in seismic velocity.

The geophysical surveying covered an extended zone, reaching from the Sydney Harbour Bridge in the east to Goat Island in the west. This gave the client detailed information to assess multiple tunnel alignment options and to find the most suitable one. The geophysical investigation defined the palaeogeographical rock surface and identified the existence of a paleo valley crossing the scoping design alignment. Thus, the alignment was revised.

This project is one of only a few projects over water to employ the use of cross-hole seismic tomography. We set up two drilling barges over water, 40 metres apart, to perform sonic scanning between the two holes. This provided additional information on the bedrock condition at the base of the paleo valley.

With close interactions between the track design, tunnel design and geotechnical teams, we produced a geological model that was suitable for the tunnel alignment and design.

Digital driven design

WSP has been recognised by the industry for our collaborative, technology driven approach in early design on the project – winning Consult Australia’s Technological Innovation award in 2016. Our approach included developing a bespoke digital engineering framework that combines data management and virtual reality to visualise customer experience and optimise tunnel and underground station design, modelling of passenger flow to optimise the location of station elements, as well as designing for future scenarios such as climate change for drainage and flooding and allowing for potential new developments.

In 2018, we were engaged in design joint venture as part of the Systems Connect group delivering the Sydney Metro City & Southwest Line-wide works package. Our design includes new infrastructure and systems, and modifications to existing infrastructure and services. WSP is designing track and overhead wiring, and traction power supply for the 15.5 km twin tunnels from Chatswood to Sydenham, as well as designing expansion works for the Sydney Metro Trains Facilities at Cudgegong, and a new stabling facility in Marrickville.

This stage of Sydney Metro is due to be completed in 2024.