The Pacific Highway connects Sydney and Brisbane in NSW. The Australian and NSW governments have been jointly upgrading the highway to provide a four lane divided road. We have been involved in its upgrade since the beginning, with numerous multidisciplinary commissions across the 20 year period.
This 20km section of highway from Warrell Creek to Nambucca Heads, is largely rural and passes through environmentally sensitive areas. Our team was keen to bring fresh thinking to its upgrade that included 15 bridges, new interchanges and access ramps, in order to mitigate the environmental impact. As part of a design joint venture, and in close collaboration with Acciona Ferrovial (Pacifico), we therefore pushed the boundaries of conventional bridge design.
Post-tensioned concrete U-girders have been used - the first time they have been used in Australia. They bring economy and span efficiency to three of the bridges that had particularly large spans and encounter flood plains and fisheries. A smart solution, they minimise riverbed disturbance due to hollow steel piles, important in an area known for its oysters. They also reduce the volume of structure within the water overall, maximising the flood plain flow rate, improving safety for communities in the area.
As an Australian first, we had to prove the robustness of this innovation to Roads and Maritime Services. Our in-house material specialists connected with the University of Technology Sydney, who were able to confirm our thinking and analysis for the steel driven piles. This endorsement, together with our BIM and 3D models, helped pull this innovation across the line.
To promote the use of 3D tools in the field of Highway engineering, we invested in a range of 3D technologies to prove the concept and aid design development. Not only did it help visualise and communicate the solution, it also improved its constructability.
This AU$830m project is jointly funded by the Australian and NSW governments. It is expected to open to traffic in 2017.
An Australian first
By using U-girders – with 2m diameter piles, hollow in the middle and only millimetre thick steel – the river sediment fills the girders, instead of being displaced and causing environmental disturbance. It also means that fewer girders are needed per deck, reducing the volume of structure within the water.
Twin U-Girders are used per deck with a 90mm thick precast Transfloor slab which is then made composite with a 210mm thick insitu deck topping. Having just two U-girders per deck cross-section significantly reduces the number of girders over the project. It also means that the deck could be designed without end diaphragms at the piers and majority of abutment locations.
The new highway alignment crossed three major waterways. We undertook 2D flood modelling to model the bridge structures and to limit the impact of the project on the surrounding water levels. The modelling was also used to inform the bridge scour assessments – as damage is caused by sediment in fast moving water – to make sure that the integrity of the bridge structures weren’t compromised during major flood events.
We also designed 50 culvert structures across the smaller creaks. Some of these culverts doubled as passage for local fauna – koala and similar. They featured ‘fauna furniture’ such as rocks, ropes, ledges and appropriate planting at the entrances, to facilitate the movement of species.