Highlighting some mechanisms of crack formation and propagation in clays on drying path

The objective of this research was to analyse the formation and propagation of cracks related to desiccation in clay and to provide a better understanding of the behaviour of two clays, a kaolinite, and a mixture of kaolinite and montmorillonite. At the macroscopic level, the strain tensors of the two clays during drying, as well as the cracking phenomenon, were studied using digital image correlation. The method is based on the determination of the local two-dimensional strains and displacements fields using the programs Vic-2D and Vic-3D. Different mechanisms of crack formation were identified: opening mode, sliding mode and tearing mode. At the end of desiccation, the cracks form a network similar to thermal fatigue or thermal shock networks. Bifurcation and coalescence of cracks can also be observed in soil. Another objective was to explore the effect of mineralogy on the behaviour of these clays. It is the reason why two different mixtures of kaolin and montmorillonite were chosen, with liquid limits ranging from 40% to 82%. The results were found to be similar in both cases, except concerning the kinetics, which is faster in kaolin.