Geotechnical Design for Major Bridge and Elevated Road Infrastructure in West Melbourne

Stephen Gamble

The design of deep foundations for large-scale transport infrastructure will not only require sound geotechnical engineering, but will likely also call for a great deal more besides. This presentation aims to share key lessons, challenges and achievements from the geotechnical design undertaken for the eastern section of the West Gate Tunnel Project i.e. including the Maribyrnong River bridge crossing and the parts eastward. The eastern section of the project traverses right across the low-lying brownfield area of West Melbourne that has variously been home to salt-flats and swamp, rubbish tip and squatter camps, land draining and reclamation works, rail-yards wholesale markets and docks. Needless to also say the area is also underlain by 30 m to 50 m of the Yarra Delta Quaternary and Tertiary sedimentary sequence. The increased scale and extent of a project tends to increase the variety of challenges, and with approximately 15 km total length of multi-lane bridges, elevated roads and ramps all supported on pile foundations, the east zone of WGTP had its fair share. Coode Island Silt is known for being challenging on embankments and at-grade works, but it also can behave badly for piling works.

The talk will look at the key steps that need to be negotiated on large infrastructure design: field investigations, ground modelling, analysis, design and documentation. Geotechnical analysis and design tools will be discussed and critiqued/compared, together with strategy suggestions for ‘supply-side’ design management when working as part of a big project team. Several of the project’s more interesting geotechnical design challenges will be shared, such as testing to positively confirm sedimentary unit identity/age, finding hidden basalt deposits, and piling in soft ground near existing assets; and the steps taken to manage or resolve these will also be described.

Finally, the talk will pose a few questions which those who follow may have for us (as today’s geotechnical practitioners): are they piling code requirements or guidance? can we keep improving design efficiency? do we have both a technical and a practical understanding of how deep foundations are built and will behave? and lastly, how important are the construction site observations, proof testing and design verification?

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.