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?

About the speaker

Stephen Gamble Geotechnical Engineer and Principal, Douglas Partners, Melbourne

Stephen Gamble is a Geotechnical Engineer and a Principal at Douglas Partners, Melbourne. His professional career spans some 34 years and has seen him working in both consulting and contracting firms in Melbourne, Hong Kong, Sydney, Sunshine Coast and Brisbane. After graduating from RMIT in 1987, and from the first cohort of students to undertake the Geological Engineering degree course, Stephen started with Maunsell & Partners in their geotechnical group.

During his first year with M&P he received training and instruction on dynamic load testing of piles using PDA equipment. This was a lucky break which has continued to open doors and lead to new opportunities over the 33 years that followed. While the hands-on activities happened mostly in the first half, it included countless dynamic tests with both PDA and TNO testing equipment (analogue and digital, old and new), numerous sonic pulse integrity tests using TNO, IFCO and PIT equipment; conducting a Statnamic test (the 2nd 16MN test at Eureka Tower), and undertaking or overseeing numerous static load tests in Hong Kong, Sydney and Melbourne. Being of a certain vintage he has also looked closely at both Melbourne Mudstone and Ashfield Shale pile sockets, dangling on a bosun’s chair or in a harness. All of these opportunities and experiences have been hugely valuable for improving his understanding of deep foundation design.

In the last five years, since returning to Melbourne and happily joining Douglas Partners, Stephen has mainly worked on larger design projects for road and rail infrastructure. He has been the Geotechnical Design Lead on the CityLink Tulla Widening Project and on the West Gate Tunnel Project – East Zone. He has also been a Douglas Partners SME and Design Reviewer for a number of level crossing removal projects undertaken by the North Western Program Alliance, including Camp Rd Campbellfield, Bell-Moreland and recently on the Bell to Preston LCRP, for which work is now underway.

Away from work, Steve is mostly found in the workshop or garden making sawdust and wood-shavings, among other things.

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