Void Ratio–Dependent Water Retention Model for a Deformable Residual Clay

Pressure plate extractor tests were performed on a residual clay soil over three drying–wetting cycles. An adjustment of a soil internal structure, caused by the change in the stress and suction path, affects the soil–water characteristic curve (SWCC). The hysteretic loop size of the suction–void ratio, as well as the deformation, is influenced by the stress and drying–wetting cycles. Lower vertical stress together with fewer drying–wetting cycles implies an increased hysteretic loop size and deformation. On the basis of experimental data, the van Genuchten model was improved to evaluate the SWCC's void ratio dependency of deformable residual clay soils. When compared with the equation proposed in the literature, SWCC's dependency on the void ratio can be well quantified based on the form of the void ratio with variable stresses and suction. This model is validated using the experimental data that are applicable to several soils subjected to various hydromechanical paths, and the experimental results are proved to match well with the model prediction. According to the second-order polynomial function relationship between each parameter and the cycle number, the SWCC obtained after five drying–wetting cycles was recommended for long-term stability analyses of unsaturated residual soils.