Experimental study of kaolin particle orientation mechanism

The aim of the experimental study is to analyse the association between the behaviour of a clayey material at the macroscopic level and its local deformation properties. The approach is based on the study of the orientation of the clay particles by scanning electron microscopy picture analysis after different phases of triaxial loading. This leads to a better understanding and characterisation of the relation between the microfabric and the strain mechanisms (i.e. contractancy and dilatancy) observed at the macroscopic level. In the initial state (one-dimensional compression), the observations highlight the microstructural anisotropy of the slightly overconsolidated specimens with a preferential orientation of the particles normal to the loading direction. During isotropic loading, densification of the clayey matrix occurs associated with a re-orientation of the particles, leading to an increase in structural isotropy, indicated by the term 'depolarisation'. On the triaxial path, up to 5% axial strain, depolarisation is reinforced. A rotation mechanism of the particles then seems to become activated beyond a critical threshold, directly related to the increase in the deviatoric part of the stress tensor.