Young Geotechnical Professionals’ Seminar & The 20th Dr Baden Clegg Award

Borehole drilling in gap-graded clayey and sandy gravels with cobbles at any location has always been a challenge to investigate and has the potential to cause major project delays and budget overruns if unsuitable drilling methods are used. This is particularly applicable when sites are remote such as in the Pilbara of Western Australia where mobilisation and availability of resources are limited and costly. This presentation discusses one such learning curve where different borehole drilling methods were used, discusses the difficulties faced with each, and the outcomes of the drilling program.

This work will present the results of an extensive field test campaign that includes more than 50 tested piles installed in sand and clay. The experimental program comprised different pile materials (mild steel, galvanized steel, and stainless steel), installation methods (hammered, vibrated, hammered + vibrated and jacked), pile diameters (89 mm, 165 mm and 450 mm), and load applications (monotonic and cyclic) to evaluate the effects of these variables on the ageing characteristics of these piles. Additionally, laboratory direct shear tests were carried out to understand better the role of the interface shear zone characteristics when ageing has taken place. A new CPT design method for driven piles was evaluated and test results showed that different pile materials, installation methods, pile diameters and cyclic load application affects the short-term and long-term (incremented) pile capacities. The conclusions seek to contribute to the understanding of the ageing mechanism of driven piles in sand and clay for offshore applications.

An overview of the prevailing site conditions will be presented with a focus on the geotechnical characterization of key units within the north wall. The function of the slope monitoring system will be explained with reference to trigger levels developed through several years of monitoring. The observations to-date will be compared to the predictions from FEM and limit-equilibrium analysis, alongside a discussion of the probable reasons for discrepancies.