Bi-Directional Static Load Testing of Large Diameters Piles in Melbourne, Australia

Bi-directional axial compression load tests using multi-level Osterberg cells (O-Cells) were undertaken on two 2.1 m diameter sacrificial test piles for the Pakenham Level Crossing Removal project in Melbourne. The purpose of the tests was to validate the design assumptions for the permanent works piles and increase the geotechnical reduction factor used for design. The target test load was 19 MN with a maximum 35 MN O-Cell loading capacity available for each pile. Both piles exceeded the design expectations from a load–displacement perspective and the maximum sustained loads were 32 MN and 24 MN for test piles TP1 and TP2, respectively. This paper presents an overview of the O-Cell test design and site setup, the test results and analysis, and the potential impact of construction methodology on pile capacity. Two CPTs were also carried out in close proximity to the test piles, prior to the load tests. The ultimate pile shaft and end bearing resistances were estimated using the CPT results and these pile capacities are compared with the load test results in this paper. The findings demonstrate that O-Cell testing can be successfully used to optimise large diameter pile lengths by adopting a higher geotechnical reduction factor in the design.