A microstructural effective stress definition for compacted active clays

The volumetric deformability of the microstructure of compacted active clays is linked to the water mass exchange with the macrostructural void space. Given that this exchange is determined by the difference in the chemical potential of water in these two structural levels, this work proposes to define a microstructural effective stress (understood as the magnitude controlling microstructural strains) from this difference in chemical potentials, identifying the microstructural effective stress with the thermodynamic swelling pressure. To assess the scope of this definition, an inspection exercise has been conducted, examining the important functional dependence on the microstructural void ratio for different loads, water content and environmental salinity conditions. For the compacted active clays analysed, the thermodynamic swelling pressure is a robust and consistent definition of the microstructural effective stress.