Sydney, NSW, Australia

WestConnex Stage 1B: M4 East Tunnels

Sydney Motorway Corporation


WestConnex is the largest road transport project in Australia, linking Sydney’s western and southwestern suburbs with the Central Business District, the airport, and Port Botany in a 33-kilometer (20.5 mi) continuous motorway that is completely free of traffic lights. 

The M4 East Project was Stage 1B of the WestConnex project and consists of approximately 16 kilometres (10 mi) of tunnel. The M4 East Project includes two mainline tunnels beneath Parramatta Road with three lanes, traveling both east and west. 

The carriageways connect to the M4 West Motorway near Homebush Bay Drive and extend to the future connection between the M4 East and the Stage 3 WestConnex. Stage 3 will provide a link connecting the M4 East and the Stage 2 new M5 tunnels at St. Peters Interchange. 

Fast Facts
  • 16 kilometres (10 mi) of tunnel
  • 2 mainline tunnels
  • Innovative shaft design

Scope of Work

Delve Underground provided the geotechnical and structural detailed design of temporary and permanent supports for the mainline tunnels including water resistant linings, cross passages, breakdown bays, substations, portals, ventilation shafts and tunnels, and temporary access tunnels. 

Delve also provided construction phase services which consisted of geotechnical tunnel face mapping, review of observed geological conditions, and selection of applicable tunnel support systems to be installed. The WestConnex M4 East tunnels were constructed by the CPB Samsung John Holland Joint Venture (CSJ).

Challenges & Innovations

To excavate the tunnels, four construction access points were built along the alignment. Delve, in collaboration with CSJ, proposed a rectangular shaft at the Underwood Road access to the tunnel level. This was strategically placed to minimize the required backfilling post construction as access to the mainline tunnel was designed to be through one of the enlarged cross passages. 

This innovative shaft design provided a rapid access point, enabling early construction of the mainline tunnel. Further, Delve was part of the design team for the unique trinocular shaft at Wattle Street.