Design and construction aspects of piled foundations for Eureka Tower Project

The Eureka Tower project involved the construction of a 300 m high 92-storey tower, the world's tallest apartment tower at the time, located in Melbourne's Southbank area. An unusual feature of the building is its slenderness, having a height to base ratio of 6 to 1. The construction of the foundations for the project proved to be a challenging task. The geological conditions at the site were complex, highly variable and posed significant construction and technical difficulties, with two layers of high to very high strength basalt above high strength Silurian Siltstone bedrock at a depth of approximately 35 m. The ground water table occurred at 2 m depth and the upper and lower basalt layers were not continuous across the site. To add to the complexity, the loadings imposed on the foundations by the structure were high. The lower basalt provided a suitable founding medium, provided that sufficient thickness was available to ensure that settlements of underlying soils were within acceptable limits. This was difficult to define because of the discontinuous nature of the lower basalt and the variable thickness of that stratum. The foundation solution that ultimately proved to be the most cost-effective was a combination of CFA piles founded on the very high strength lower basalt flow and Bored piles constructed under bentonite drilling fluid founded in the high strength Siltstone when there was insufficient thickness of the lower basalt. This paper discusses the design and construction aspects of the piled foundations for these challenging conditions, including the additional site investigation required to define areas appropriate for each pile type; construction of the piles and the special techniques required to ensure clean bases for the heavily loaded piles; and the testing regime that comprised Statnamic and Dynamic pile loading tests.