An experimental investigation into the micromechanics of non-active clays

The paper presents an experimental investigation into the micro-mechanisms controlling the behaviour of non-active clays. Clay microstructural behaviour was investigated via Mercury Intrusion Porosimetry accompanied by Scanning Electron Microscope images. To gain insight into the mechanisms underlying reversible and non-reversible compression, samples for MIP testing were taken along both normal compression and unloading-reloading lines. To investigate the nature of inter-particle forces, the response of clay samples prepared with deionised water (characterised by acidic pH) was compared with clay samples prepared with alkaline water. A high pH 'deactivate' the edge-to-face contacts that are indeed active in the clay prepared with deionised (acidic) water. The pore-size distribution data clearly highlighted that the smaller pores are associated with particles in non-contact configuration, i.e. only interacting via the overlap of the repulsive electrical field generated by the negatively charged faces. On the other hand, larger pores are associated with contact configuration, generated by the attraction between the positively charged edge and the negatively charged face of the clay particle. The pore-size distribution data also allowed inferring that reversible behaviour is mainly associated with the reversible overlap of the repulsive electrical field in contact configuration whereas the plastic response appears to be associated, at the micro-scale, with the loss of edge-to-face contacts. Finally, an embryonic 1-D discrete element model was developed to show the potential of the micromechanical conceptual model to be implemented into a DEM model.