Relationships between cracking, strains and proportions of clay matrix and rigid inclusions in Tournemire clay rock

A clay rock sample from the Tournemire Underground Research Laboratory (Averyon, France) was subjected to a fast desiccation in the laboratory, from 98 to 33% relative humidity. At the millimetre scale, fracture locations were identified and desiccation strains and fracture apertures were calculated by digital image correlation on a surface of 5.5x4.1 mm2. After the desiccation, the microstructure of this surface was mapped under scanning electron microscopy by a large mosaic of back scattered electron images in high resolution. The aim of the study is a quantitative comparison between local strains and crack apertures to the local proportion of clay matrix and rigid inclusions of the sample, in order to understand better the role of microstructure in desiccation mechanisms in clay rocks. The results have shown that: a) the crack apertures are heterogeneous and seem to be higher at some interfaces between rigid inclusions and matrix, and b) the strains are heterogeneous and their intensity is not directly related to the proportion of clay matrix at the millimetre scale. The interpretation of the dataset emphasizes the need for a microstructural approach to understand and model desiccation deformation and cracking mechanisms in clay rocks