Innovative design for drainage structure on deep soft ground

A new northern access road located to the north of the existing Airport Drive on a currently undeveloped area was proposed by Brisbane Airport Corporation to link the new duplicated Gateway Motorway to the Brisbane international and domestic terminals. One of many design and construction challenges faced in this project was to build five drainage structures on deep soft ground at specified locations to enable excavation of a drainage channel underneath the pavement in future, to divert flood water across the alignment without affecting traffic or causing adverse impacts on the structure itself and adjacent embankments. Considering the presence of deep compressible clays, it was critical to employ appropriate ground improvement techniques to reduce in-service settlements along the embankment and in particular adjacent to rigid piled structures. In addition to the appropriate ground treatment, design of cost-effective retaining structures to confine earth behind the abutment piles, with a view to controlling ground displacements and improving long-term stability, also became a critical item to be resolved during the design phase. This paper discusses the design of the structure approaches, the retaining structures and the pile foundations associated with the construction of drainage structure A within the west area of the project.