Hunter Expressway Flyover – Branxton, New South Wales.


Branxton, New South Wales



Hunter Expressway Alliance


BG&E Sydney
Hunter Expressway Flyover

The Hunter Expressway Alliance which included New South Wales (NSW) Roads and Maritime Services (RMS), Thiess, WSP and Hyder Consulting, designed and built the 13-kilometre of the Hunter Expressway. This section runs from the Newcastle interchange on the Pacific Motorway to the New England Highway, West of Branxton.

It comprises a four-lane expressway, including interchanges at the Pacific Motorway and Buchanan, 840-metres of viaduct including three bridges, bridges at many other locations and the treatment of extensive disused underground mine workings.

This important infrastructure project provide critical connectivity across the State’s road network.

BG&E provided the design and documentation for the flyover bridge which forms the Branxton-to-Sydney ramp. This bridge spans five metres wide and 156 metres long and was constructed using the incrementally launched method.

BG&E’s design solution incorporated the following key features:

  • the geometry of the bridge was such that it had to be launched on a tight combined horizontal and vertical curve. Using 3D modelling, our team ensured the set out of the cast bed and supports were compatible with the road alignment;
  • the design was developed to utilise the contractor’s existing launch equipment throughout, with only minimal modifications required to the launch nose, to account for the bridge curvature;
  • the location of the bridge was subject to significant vertical and horizontal ground movements due to potential mine subsidence. While the vertical movements were reduced through a mine void filling programme, the horizontal movements required unique articulation of the bridge structure and the use of sleeved piles at piers one and two, to isolate the structure from the ground movement;
  • the sleeving of the piles was required in consideration of the mine subsidence, which included generating 23-metre long cantilevered pile sections, that deflected significantly during launching. BG&E’s developed a temporary solution of tiebacks and props to control this movement and to ensure a safe launch; and
  • a prestressing scheme was also developed by BG&E which enabled the removal of traditional second stage prestressing and provided a 25% reduction in prestress quantities, compared to concentric stress only box.