A hysteretic soil-water retention model accounting for cyclic variations of suction and void ratio

The paper presents a water retention model capable of predicting the hysteretic response of soils during both wetting–drying cycles at constant void ratio and compression–swelling cycles at constant suction. In the proposed model two main surfaces – the main wetting and main drying surfaces – enclose the domain of attainable soil states in the degree of saturation–suction–void ratio space. Inside this domain, the variation of degree of saturation is governed by a reversible scanning law, which describes the transition from one main surface to the other. A simplified calibration procedure is presented to select the values of the four parameters defining the two main surfaces by using a minimum of two compression tests at constant suction and one drying test at constant mean net stress. Model computations are validated against results from an experimental campaign on a compacted mixture of bentonite and kaolin. The proposed formulation is capable of capturing important soil features, such as the influence of hydraulic hysteresis and deformation on the variation of degree of saturation, and the dependence of water retention behaviour during compression on previous wetting–drying history. Moreover, during main wetting or main drying at high suction (i.e. at low saturation), the model correctly predicts a ‘virgin' retention line that uniquely relates water ratio and suction regardless of the current value of void ratio.