An investigation into the water retention behaviour of deformable soils

The paper presents an experimental and modelling approach for the soil water retention behaviour of two deformable soils. The objective is to investigate the physical mechanisms that govern the soil water retention properties and to propose a constitutive framework for the soil water retention curve accounting for the initial state of compaction and deformability of soils. A granular soil and a clayey soil were subjected to drying over a wide range of suctions so that the residual state of saturation could be attained. Different initial densities were tested for each material. The obtained soil water retention curves are synthesized and compared in terms of water content, void ratio, and degree of saturation, and are expressed as a function of the total suction. The studies enable to assess the effect of the past and present soil deformation on the shape of the curves. The void ratio exerts a clear influence on the air entry value, revealing that the breakthrough of air into the pores of the soil is more arduous in denser states. In the plane of 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 are convergent. The observed features of behaviour are conceptualized into a 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 and can thus be generalized into a hysteretic model applicable to drying-wetting cycles. The calibration of the model requires the 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.