Volume change behaviour of a compacted scaly clay during cyclic suction changes

The research presented in this paper focuses on the investigation and modelling of the volume change response of compacted tectonised clay samples subjected to several wetting and drying cycles in controlled-suction oedometers. Oedometer tests were carried out under different values of constant vertical net stress, and wetting and drying cycles were performed varying applied matric suction between 10 and 800 kPa. The investigation was complemented with a study of the material microstructure to support the interpretation of the overall mechanical response. At a microscopic level, the material is characterized by different types of particle assemblages, scales, and clay aggregates. One of these assemblages was also subjected to a relative humidity cycle in an environmental scanning electron microscope (ESEM) to investigate the reversibility of the mechanical response. Based on the experimental results, the clay volume change behaviour is discussed and interpreted within the context of a double structure elastoplastic model. The procedure used to derive elastic and plastic constitutive parameters is presented. Comparison of test results with model predictions shows a satisfactory agreement between measured and calculated strain evolution.