Eureka Tower, A Bored Pier Foundation Story

Max Ervin, Golder Associates, Melbourne

The Eureka Tower Project is a 300 m high 88 level residential building, constructed in the Southbank precinct of Melbourne, Australia. The site is underlain by complex geology, including near surface soft clays, a shallow layer of Quaternary Age basalt which covers part of the site, a lower very high strength basalt layer at about 20 m depth and again covering only part of the site, with high strength Silurian Age siltstone as the basement rock at about 30 m depth.

Unusually extensive site investigations were undertaken for the project due to the complex geology. Piled footings were required, but due to the very high strength of the lower basalt (UCS up to 250 MPa) it was desirable as far as practical to found on this material. A hybrid piling solution was developed, with 750 mm diameter CFA piles founding on the lower basalt over part of the site, and 1.2 m diameter bored piles socketed into the siltstone used elsewhere. Two CFA test piles were constructed, with Statnamic and dynamic load tests then performed. Dynamic testing was then undertaken on a number of the prototype piles.

The bored piles were designed to accommodate working loads of up to 22 MN. An allowable base resistance of up to 20 MPa was considered acceptable for the very high strength siltstone. However, settlement compatibility with the CFA piles founding at shallower depth on the basalt was necessary. The adopted socket in the siltstone was therefore based on predicted settlement, with the socket length assessed using the program ROCKET.

The talk will describe this case history.

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