Sydney is a world-class business and tourism destination which makes high quality transport links essential. As one of Australia’s largest integrated transport projects at time of construction, WestConnex M8 duplicated the existing, heavily congested M5 East tunnel, to separate city bound and airport bound traffic from Sydney’s south-west suburbs.

This has helped to reduce travel time between Liverpool and south Sydney by up to 30 minutes, making it easier to connect people and places.

Aurecon, in a design joint venture with Jacobs, provided engineering design services and construction phase services to the CPB Dragados Samsung Joint Venture (constructor), for owner and operator, Transurban and Transport for NSW.

The duplicated twin underground 9 km motorway tunnels incorporate capacity for three lanes if required to accommodate potential future traffic growth. A new 4 level interchange, incorporating 12 complex precast segmental bridges at St Peters, connects the tunnels to surface routes through to Alexandria and Mascot, and Sydney International Airport.

An engineering design like no other

The WestConnex M8 tunnels are 5.1 m tall, significantly taller than the average 4.6 m for traditional road tunnels, in order to service future possible heights of freight vehicles. This project was an engineering design like no other, with a 20 m tunnel roof span, making it the widest in Australia at the time of construction.

A thinner layer of shotcrete for the tunnel lining was engineered to significantly reduce the overall volume and weight of shotcrete, making the span width possible while still meeting all tunnel design and safety requirements. Enhanced fire protection was achieved by adding fibre reinforcement polymers to the shotcrete to improve its strength and resistance to fire and heat.

The WestConnex M8 tunnels through the Arncliffe section were mined at a depth of 75 m to cross under a deep palaeochannel and the Cooks River. One section of the tunnels involved large numbers of sub-vertical inclined joints with open fractures up to 340 mm wide. To control water inflow into the tunnels in this section, the project team devised a solution to surface grout the fractures before tunnel excavation commenced. Borehole televiewers identified each fracture to be successfully filled, thus providing a foundation for a more cost-effective underground grouting programme during construction.

The scale and complexity of this project is not to be underestimated. More than 17,000 engineering drawings were delivered in 24 months. To enable this to be achieved, Aurecon developed a digital collaboration portal to house engineering designs, documents, and cost and performance tracking information for design approvals.

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