Geotechnical design for the Port Botany expansion project, Sydney

Abstract

This paper describes ground treatments, foundation preparations and geotechnical design for extensive reclamations and retaining structures forming the Port Botany expansion project in Sydney, Australia. The 63 ha reclamation, up to 30 m deep, is constructed from dredged Botany Bay sands, which are retained by over two hundred 20 m high counterfort and blockwork gravity wall units. These berth structures are founded on vibrocompacted sand backfill placed within a submerged trench excavated into natural fissured clays. The design involved detailed assessment of stability and movement behaviour for the reclamation and berth structures. Geotechnical compliance testing criteria were developed for reclamation fill materials to provide compaction and material quality assurance. In particular, acceptance criteria for berth structure foundations and retained backfill were developed to verify the strength and stiffness of fills so as to meet design requirements at key time milestones following handover of the works. The main fill verification tool utilised cone penetration tests, for which screening rules and site-specific acceptance criteria were developed. Methods of fill compaction included dynamic compaction, vibrocompaction and impact roller compaction. The relative performance of these methods is discussed, along with compliance testing results, effects of vibrocompaction on wall structures, fill variability and actual compared with predicted performance of compacted sand fills.