An experimental investigation into the behaviour of de-structured chalk under cyclic loading

Liu, T., Ahmadi-Naghadeh, R., Vinck, K., Jardine, R. J., Kontoe, S., Buckley, R. M. and Byrne, B. W. (2023) An experimental investigation into the behaviour of de-structured chalk under cyclic loading. Geotechnique, (doi: 10.1680/jgeot.21.00199) (Early Online Publication)

Abstract

Low-to-medium density chalk can be de-structured to soft putty by high-pressure compression, dynamic impact or large-strain repetitive shearing. These process all occur during pile driving and affect subsequent static and cyclic load-carrying capacities. This paper reports undrained triaxial experiments on de-structured chalk, which shows distinctly time-dependent behaviour as well as highly non-linear stiffness, well-defined phase transformation (PT) and stable ultimate critical states under monotonic loading. Its response to high-level undrained cyclic loading invokes both contractive and dilative phases that lead to pore pressure build-up, leftward effective stress path drift, permanent strain accumulation, cyclic stiffness losses and increasing damping ratios that resemble those of silts. These outcomes are relatively insensitive to consolidation pressures and are distinctly different to those of the parent intact chalk. The maximum number of cycles that can be sustained under given combinations of mean and cyclic stresses are expressed in an interactive stress diagram which also identifies conditions under which cycling has no deleterious effect. Empirical correlations are proposed to predict the number of cycles to failure and mean effective stress drift trends under the most critical cyclic conditions. Specimens that survive long-term cycling present higher post-cyclic stiffnesses and shear strengths than equivalent ‘virgin’ specimens.

• Item Type: Articles
• Additional Information: The experimental study was undertaken as part of the ALPACA and ALPACA Plus Projects funded by the Engineering and Physical Science Research Council (EPSRC) through grant EP/P033091/1 held by Imperial College London and University of Oxford.
• Status: Early Online Publication
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Buckley, Dr Roisin
• Authors: Liu, T., Ahmadi-Naghadeh, R., Vinck, K., Jardine, R. J., Kontoe, S., Buckley, R. M., and Byrne, B. W.
• College/School: College of Science and Engineering > School of Engineering > Infrastructure and Environment
• Journal Name: Geotechnique
• Publisher: ICE Publishing
• ISSN: 0016-8505
• ISSN (Online): 1751-7656
• Published Online: 12 January 2022
• Copyright Holders: Copyright © 2022 ICE Publishing
• First Published: First published in Geotechnique 2022
• Publisher Policy: Reproduced in accordance with the publisher copyright policy