A Multi-Technique Solution to Overcome Geotechnical, Structural and Physical Challenges on a Southbank Project

Dr Eric Chong

The inner-city suburb of Southbank VIC has seen significant growth in the last decades due its strategic location just south of the Yarra River with Melbourne CBD being a walking distance away. High-rise developments have been a constant feature in this area where the scarcity of land has pushed new projects into smaller acreage. The ever importance of maximising every millimetre of a real estate especially in this district means new towers being constructed in close proximity to existing adjacent properties are becoming increasingly common and challenging. As the Southbank region is commonly underlain by a thick layer of soft marine clay with a high groundwater table, geotechnical design and construction of retaining wall and foundation applications can be complex in this area.

From a piling contractor’s point of view, this presentation details the D&C process of a mixed-use project in Southbank where a range of geotechnical techniques were able to help the project achieve its desired objectives. The site is sandwiched between two adjoining structures which presented considerable spatial and design difficulties. A 6m deep core/car stacker excavation in this ground condition (loose sands underlain by a thick and soft clay with a high water table) was proposed on the boundary next to the sensitive neighbouring assets. A tight deflection criterion was imposed on the retention system compounded by the physical challenge of installing the retention system as close to the boundary as the client required. To overcome these issues while also achieve economical and favourable program outcomes, a multi-technique hybrid retention system comprising sheet piles, soldier piles and wet mass soil mixing with internal struts was developed, together with a unique installation method of the piles along the boundary to meet the geotechnical, structural, and spatial requirements of the project.

For the foundation scope, the presentation will share the formulation of the foundation solution for the building loads and the selection of effective piling techniques and rigs based on the complex geotechnical risks encountered involving soft clays, a basalt tongue and a deep bedrock coupled with more physical challenges posed by an existing substation. These complexities resulted in the utilisation of two different piling techniques – continuous flight auger (CFA) and driven precast – being successfully carried out on this project. The presentation aims to also cover the testing requirements and results achieved on the piling and ground improvement works.

About the speaker

Dr Eric Chong Engineering Manager, Keller

Dr Eric Chong is an Engineering Manager at Keller where he oversees D&C projects across Victoria, South Australia, and Tasmania. Eric completed his bachelor’s degree and subsequently a PhD at Monash University where his research was in the area of rock-socketed piles. Eric joined Keller in 2011 and has since been involved in the delivery of projects ranging from 7-level basement to CFA piling deeper than 50m to big diameter single monopile carrying loads in excess of 140MN.

Within the Keller global network, Eric is part of the CFA piling Global Product Team providing support and advice on the piling technique for applications around the world. Eric is a Chartered Professional Engineer and a Fellow of Engineers Australia. He is a frequent guest lecturer at local universities and a committee member for the new AS4678 – Earth Retaining Structures.

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