WestConnex M8, Sydney, Australia

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WestConnex M8, Sydney, Australia

Engineering a 9-kilometre tunnel to provide Sydney motorists with a traffic-light free link and reduced commuting times

WestConnex M8 is one of Australia’s largest integrated transport projects and duplicates the existing, heavily congested M5 East tunnel, east of King Georges Road, to separate city bound and airport bound traffic from Sydney’s south-west suburbs.

Sydney is a world-class business and tourism destination which makes high quality transport links essential. The AUD$4.3 billion project has helped 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 engineering role incorporated:

M8 the connection enabler

WestConnex M8 comprises of twin underground motorway tunnels, 9-kilometers in length, with two lanes in each direction from Kingsgrove to St Peters. Future capacity for three lanes has been incorporated to accommodate future traffic growth.

The tunnels include underground connections to the WestConnex M4-M5 Link tunnels and Rozelle Interchange, opening in 2023, and the M6 extension, currently in planning stage.

The four-level interchange incorporating 12 complex precast segmental bridges at St Peters connects the M8 to surface routes through to Alexandria and Mascot, and Sydney International Airport.

An engineering design like no other

Engineers provided detailed design for the ventilation shafts and tunnels, temporary access tunnels, electrical substations, cross passages, mainline tunnels, breakdown bays and portals.

It was an engineering design like no other with a 20-metre tunnel roof span, making it the largest in Australia.

A thinner layer of shotcrete for the tunnel lining was engineered to significantly reduce the overall volume of shotcrete required in construction, 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 tunnels are 5.1-metres tall, significantly taller than the average 4.6-metres for traditional road tunnels, in order to service the future anticipated increased height of freight vehicles.

Engineering timeframe process

Engineering timeframe process

Engineers faced a challenging timeframe within the design and construct process with more than 17 000 engineering drawings delivered in 24 months.

The Digital Engine developed by Aurecon was a collaboration portal that housed engineering designs, documents, and cost and performance tracking for design approvals. Learn more about how Aurecon managed the M8 design process using its collaboration portal in the case study below:

Bringing the power and lights online

More than 2 000-kilometres of power cable, in addition to communication cabling, fire sprinklers and hydrants, and cameras are nestled in the crown of the tunnel roof. To accommodate the tall height of the tunnel, engineers designed a modular construction sequence to compactly fit these services in the roof cavity and streamline the installation sequence.

To safely guide motorists through the M8 tunnels, in excess of 7 500 LED lights were installed for wayfinding, security and safety. The intelligent transport system engineers designed a network of communications for electronic directional signage in the tunnels, traffic detection and monitoring devices and tunnel closure devices.

With so much cabling, lights and electronic signs, engineers departed from the traditional approach to host substations at surface level, instead bringing the four electrical substations underground. This approach means less electrical cabling and more efficient distribution of power to where it is needed in the tunnel.

The substations are housed in large cross passages that allow services to cross from one tunnel to the other, thus enabling a series of circuit rings for high-voltage power and water main services. The larger than average cross passages engineered for M8 also provide escape routes for people from the incident tunnel to the non-incident tunnel in case of emergencies.

Ground geology unearths a challenge

The WestConnex M8 tunnels through the Arncliffe section were mined at a depth of 75 metres to cross under a deep palaeochannel and Cooks River. This section had large numbers of sub-vertical inclined joints with open fractures up to 340-millimetres wide.

To control water inflow into the tunnels in this section, engineers 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 program during construction.

At a glance, WestConnex M8 consists of:

  • 9-kilometre twin road tunnels from M5 East at Kingsgrove to the new four-level interchange at St Peters
  • Two primary tunnel cross sections for two, three and four lanes
  • A new four-level interchange at St Peters that includes complex interweaving of on and off ramps with 12 large precast segmental box girder bridges
  • Four 20-metre high, ventilation shafts; located at the western portal (at Kingsgrove, Bexley and Arncliffe) and the eastern portal (at St Peters)
  • Four underground electrical substations

WestConnex M8 directly benefits millions of people every day through safer connections to communities, and more efficient travel times for freight and cars. It is more than just a road, it is a vital piece of infrastructure that is getting Sydney moving now and into the future.

The project opened to traffic in July 2020. It is part of the WestConnex master plan to create a 33-kilometre, traffic-light free, motorway network.

The Authors would like to thank CPB Dragados Samsung Joint Venture who were responsible for the design and construction of the project and the asset owner/ operator, WestConnex | Transurban for permission to publish this paper.


Learn more about Aurecon's work on the Westconnex M4–M5 Link, stage 3 of the Westconnex Road Infrastructure Project.

 

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