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Solving complexities on Australia’s deepest road tunnel





New motorway link for traffic returns neighbourhood streets to north-west Sydney communities.

NorthConnex is a 9 km tunnel reaching a maximum depth of 90 m, making it Australia’s deepest road tunnel. Motorists are now able to travel from Newcastle to Melbourne without a single set of traffic lights, paving the way for more efficient state and national freight movements.

The tunnel delivers significant benefits to local communities around Pennant Hills Road, Sydney, taking 5,000 trucks a day off neighbourhood streets.

Digital engineering tackles variable tunnel profiles

Engineers turned to digital engineering tools to develop, streamline and validate the definition of the complex variable tunnel geometry. A fully optimised spatial model enabled the design and construction teams to visualise the changing geological requirements as well as varying geometrical requirements, such as underground junctions, traffic merges and diverges, cross passages, jet fans and traffic signs.

The engineering design used the sequential excavation and support method; using roadheaders to excavate the tunnel, with a combination of rock bolts and sprayed concrete applied close to the tunnel face to support excavation. In this way, the efficient tunnel design solution is that each cross section is cut specifically to the geometrical requirements at any given location. This resulted in less excavation and spoil to move.

Sustainability in design

NorthConnex was awarded a ‘Leading’ Infrastructure Sustainability (IS) Design rating by the Infrastructure Sustainability Council of Australia (ISCA). A ‘Leading’ IS rating is the highest possible achievement in the IS rating scheme and indicates the project is achieving best practice in sustainability. NorthConnex is the first road tunnel in Australia to achieve a ‘Leading’ rating.

The project was able to achieve this by implementing sustainable design practices and construction techniques, including reducing emissions through the use of LED lighting, modelling reduction in water use throughout construction and reducing the lifecycle impacts of materials through initiatives focused on locally sourced, reclaimed and recycled content for construction. More than 2.5 million cubic metres of soil was excavated and 100% was reused.