The Coopernook to Herons Creek Alliance was formed with the New South Wales Roads and Traffic Authority (RTA), Parsons Brinckerhoff and Thiess Contractors to design and construct the upgrade of 32.7 km of the Pacific Highway to dual carriageway between Coopernook and Herons Creek on the NSW Mid-North Coast. The upgrade works involved the construction of 15 new bridges, including two major river crossings over the Stewarts River and the Camden Haven River, which will duplicate the existing bridges. Both bridge approaches were constructed on embankments supported by a geotextile reinforced granular platform over soft ground adjacent to the existing bridges. Embankment movement, if significant, would not only affect the pavement performance but also impose additional loads on the piles supporting the adjacent bridge structures.
To mitigate settlement effects, the bridge approach treatment works consisted of displacement columns to support the bridge approach embankments and a geotextile reinforced load transfer mat constructed on top of the displacement columns to assist in distributing embankment load. The main challenges were construction on soft ground, requirements to maintain design life of the existing bridges and the need for an accelerated construction technology for timely delivery of the project. This paper outlines the project, presents the case history of the bridge approach treatment works, and discusses analysis, design and construction monitoring.