Hunter expressway, Australia: dealing with poor ground and subsidence

The A$1·7 billion (£1·13 billion) Hunter Expressway project near Newcastle, Australia, is an impressive 40 km motorway traversing a floodplain and rugged terrain by means of a series of bridges, viaducts and massive earthworks. Former underground coal mining activities and poor ground conditions presented exceptional engineering and construction challenges. Subsidence movements associated with the sudden collapse of standing pillars could leave some of project's structures unserviceable, while earthworks feature a proportionally large amount of poor quality materials derived from cutting construction. The designers incorporated expansive and carbonaceous materials, which would otherwise be spoiled because of their poor engineering properties. This paper chronicles the unique design and construction challenges associated with earthworks and mine subsidence for the eastern section of the project.