Cyclic Characterisation of Low-to-Medium Density Chalk for Offshore Driven Pile Design

Liu, T., Jardine, R., AHmadi-Naghadeh, R., Kontoe, S., Buckley, R. , Byrne, B. and McAdam, R. (2023) Cyclic Characterisation of Low-to-Medium Density Chalk for Offshore Driven Pile Design. In: 9th International SUT OSIG Conference “Innovative Geotechnologies for Energy Transition”, London, UK, 12-14 Sep 2023,

Abstract

Project-specific advanced laboratory testing is employed increasingly frequently in site investigations for major offshore projects. Such testing needs to focus on characterising properties under in-situ conditions, while also catering for the effects of foundation installation and subsequent service conditions, including cyclic loading. Low-to-medium density chalk, a variable soft biomicrite, can be de-structured to soft paste under dynamic percussion or large-strain repetitive shearing, posing significant challenges and uncertainties for driven pile design. This paper draws on key outcomes from undrained cyclic triaxial test programmes on both intact chalk and dynamically de-structured (putty) chalk. The cyclic response of intact chalk resembles the fatigue behaviour of hard rocks and develops little sign of damage before sharp pore pressure reductions and brittle collapse occurs. In contrast, fully de-structured chalk develops both contractive and dilative phases, as seen with silts. The associated effective stress reductions vary systematically with the number of cycles and cyclic stress ratio. A laboratory-based global axial cyclic predictive method is proposed from the experiments and employed to predict the outcomes of field axial cyclic loading pile tests. The research provides then basis for robust cyclic design guidance for piles driven in low-to-medium density chalk.

• Item Type: Conference Proceedings
• Additional Information: The study was part of the ALPACA project funded by Engineering and Physical Science Research Council (EPSRC) grant EP/P033091/1, Royal Society Newton Advanced Fellowship NA160438 and Supergen ORE Hub 2018 (EPSRC EP/S000747/1).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Buckley, Dr Roisin
• Authors: Liu, T., Jardine, R., AHmadi-Naghadeh, R., Kontoe, S., Buckley, R., Byrne, B., and McAdam, R.
• College/School: College of Science and Engineering > School of Engineering > Infrastructure and Environment

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