Fabric and clay activity in soil water retention behaviour

Modelling the water retention behaviour requires proper understanding of all the processes which affect the amount of water stored in the pore network, depending on the soil state and the soil history. Traditionally, in many applications a single water content - suction curve is used. This approach limits the applicability of the retention data to practical cases, especially when fine grain soils are dealt with, when the deformability and activity of the clay fraction significantly affect the interaction with water. On the other side, water retention is being recognised more and more as a fundamental information in the description of the mechanical response of the soil, as it provides the key connection to the partial volumetric strains in a deformation process. With reference to the work performed at the Politecnico di Milano in the last years, a contribution on the understanding and modelling the coupled water retention-mechanical response in deformable soils is presented. The contribution aims to: (i) summarise the mechanisms which contribute to water retention; (ii) point out the role played by an evolving fabric and the fluid properties on water retention; and (iii) provide an overview on some of the consequences of evolving water retention properties on the mechanical behaviour.