Investigation into the hydration- and compression-induced damage of Callovo-Oxfordian claystone

Examination of the microstructure and mineral composition of Callovo-Oxfordian (COx) claystone revealed the presence of clay matrix intruded by a large amount of mineral inclusions such as carbonate and quartz. This claystone can be damaged when wetted/dried due to the swelling/shrinkage of clay matrix, or when subjected to mechanical loading due to the loss of bonds formed among mineral grains. The damage of COx claystone was evidenced in the literature by analysing its pore size distribution curves after wetting/drying and mechanical loading, obtained from the mercury intrusion porosimetry (MIP) tests. In this paper, a damage coefficient accounting for the physics of damage (i.e. generation of cracks) was adopted, corresponding to the proportion of cracks in the total porosity. This coefficient enables the description of the effect of cracks on the overall mechanical behaviour of COx claystone. Based on the MIP results, the evolution of the damage coefficient with the effective stress and plastic volumetric strain was identified for COx claystone, during both the hydration and the oedometer compression processes.