Ground Improvement over Soft Clay for the Main Access Road to and from Port Macquarie Airport

This paper describes the selection and design of ground improvement for a 260 m section of the upgrade of Boundary Street forming the main access road to and from Port Macquarie Airport. Boundary Street is currently a single-lane (each direction) road constructed over soft clay which extends to a depth of 10 m for a 260 m section of the project. It is the only access to and from the regional airport and future business park and is subject to flooding during minor event. In 2017, Port Macquarie and Hastings Council proposes to upgrade the road to twin carriageways in each direction cater for the predicted growth of the airport and the demand for increased capacity within the surrounding infrastructure. A number of solutions to deal with the soft ground conditions were considered, including building a bridge, or ground improvement techniques to reduce post-construction settlement and differential settlement following the road upgrade. Ground improvement options including surcharging with or without wick drains and the use of rigid inclusions were considered. A major constraint on the choice of ground improvement options was the adjacent wetland and sensitivity of fauna habitat to construction activities. Following an extensive optioning study, the use of rigid inclusions was adopted to provide a balanced solution between cost and minimising the risk of damaging adjacent wetland and its habitats. The design optioneering process and design of the rigid inclusion ground improvement are presented in this paper.