Eureka Tower

Eureka Tower
Grocon Pty Ltd
Techniques Used: 
Deep, Large Diameter Bored and Concrete Injected CFA Piling

Project Brief: The Eureka Tower project involved the construction of a 300m high 92-storey tower, the world’s tallest apartment tower at the time, located in Melbourne’s Southbank area.

An unusual feature of this building is its slenderness, having a height to base ratio of 6 to 1. Very high strength concrete of 100MPa was used in the columns.

Geological Conditions: The conditions at the site were complex primarily due to two layers of basalt occurring above the Silurian Siltstone bedrock that occurs at a depth of about 35m. The basalt was of very high strength, indicated by testing to be in excess of 200MPa, and was not continuous across the site for either the upper or lower flow. To add to the complexity, the loadings imposed on the foundations by the structure were high.

Scope of Work: Continuous Flight Auger (CFA) piles were used where conditions were suitable for founding on the lower basalt. Where conditions were not suitable, bored piles were socketed into the siltstone.

The final solution comprised 28 bored piles of 1200mm nominal diameter socketed into siltstone, and 243 CFA piles of 750mm diameter founded on the lower basalt. The solution reduced the foundation costs by more than 30% and enabled the programme to be achieved.

Approximately 75% of the CFA piles required predrilling through the very high strength upper basalt layer, which was up to 5.5m thick. CFA piles were then drilled to effective refusal on to the lower basalt. All CFA piles were constructed with full computer monitoring.

Bored piles were used where the basalt was not suitable for CFA piles and this required drilling through the two layers of basalt to socket into the siltstone at a depth of approximately 35m. Construction under bentonite drilling fluid was specified as the most economical approach for the difficult conditions.

Drilling through rock of up to 300MPa strength was made possible only because of locally designed and built, high performance drilling rigs, equipped with appropriate drilling tools, also designed and manufactured by Vibropile.

Conclusion: A cost effective and innovative solution for the foundations for the Eureka Tower project was brought about by co-operation between consulting structural and geotechnical engineers and piling contractors, in what where extremely difficult geotechnical conditions.

The application of different pile types was innovative and the construction performed on time in difficult circumstances compounded by the restricted space available on site.