Investigations on water retention behaviour of deformable soils

The trend in modern unsaturated soil mechanics is to enhance the physical understanding of the soil water retention properties. It is agreed that the retention characteristics depend on the state of compaction and are related to the deformability of the media. Therefore, any appropriate experimental set up and behavioural model shall take into consideration the evolution of the density state in the course of drying or wetting processes. The results from an exhaustive experimental characterization of the retention behaviour of a granular soil is synthesized. The information concerning degree of saturation, suction and void ratio is assessed to quantify in particular the effect of the passed and present states of mechanical stress and strain on the shape of the curves. The void ratio is noticed to exert a clear influence on the air entry value. In the plane water content versus suction, the experimental results highlight the fact that from a certain value of suction, the retention curves corresponding to different densities of the same soil converge into a single curve. The observed features of behaviour are conceptualized into a new modelling framework expressing the evolution of the degree of saturation as a function of suction. The proposed retention model makes use of the theory of elasto-plasticity. The calibration of the model requires experimental retention data for two initial void ratios. The prediction of tests for further ranges of void ratios proves to be accurate which supports the adequacy of formulated concepts.