Multi-scale experimental investigation into micro-mechanical behaviour of clays

Background

The macroscopic response of geomaterials is controlled by the processes occurring at the microscale. Understanding these processes is key to interpret experimental data, inform ‘continuum’ macroscopic constitutive models, and to develop quantitative predictive tools based on discrete numerical approaches. For the case of granular materials, microscale mechanisms have been investigated experimentally in terms of inter-particle forces and particle kinematics and these have been translated into DEM models, which have been used as virtual laboratory to investigate fundamental aspects of macroscopic behaviour of granular materials. On the other hand, microscale processes in clays cannot be easily investigated experimentally in a direct fashion due to the small size of clay particles. In addition, interactions between clay particles are strongly affected by the pore-fluid-mediated electrochemical forces and this makes clay micromechanical behaviour more complex to understand and model. Despite 100 years of research on the macro-mechanical behaviour of clay, we are still largely ignoring underlying mechanisms at the particle scale.

Research project

The research aims to link clay behaviour across scales, from nano through micro to milli scale. The nature and the magnitude of clay particle electrical charge rule particle-to-particle interactions and will be investigated via a blend of methods (cation exchange, titration, electrophoresis). Its impact on particle interactions and aggregation will be theoretically investigated by solving numerically the Poisson-Boltzmann equation in order to understand fundamental modes of clay particle interaction. Particle scale processes at the microscale will then be explored via X-ray Computed Tomography and linked to the response observed at the milliscale in compression tests where the clay is tested under different pore-water chemistry (electrolyte concertation, pH, and fluid polarity) up to 1 GPa.

The outcome of the research consists in elucidating fundamental mechanisms underpinning clay behaviour including reversible and non-reversible response, nature of energy dissipation, and anisotropic behaviour.