Modelling the evolution of water retention hysteresis loops during soil deformation based on the ink-bottle effect

The ink-bottle effect, resulting from the heterogeneous pore structure, plays a significant role in the hydraulic hysteresis of water retention behavior. Experimental evidence indicates that volumetric deformation extensively influences the hysteresis characteristics of the soil-water retention curve (SWRC). This paper presents a physical-based model that aims to simulate the contraction of the hysteresis loop in the SWRC during soil compression by considering the evolution of the ink-bottle effect. Within the proposed model, it is assumed that the suction increment is consumed in two distinct manners: to overcome the ink-bottle effect and to alter soil saturation. As soil undergoes compression, the ink-bottle effect weakens, resulting in a reduced proportion of suction consumed in counteracting this effect. To quantitatively describe the impact of ink-bottle effect evolution on SWRC hysteresis, a novel concept known as hysteresis potential is introduced, which is defined as the difference in natural logarithmic values of suction between the drying and wetting curves at a given saturation. Finally, the proposed model was validated using five sets of experimental data, affirming its capability to capture the hysteresis loop evolution in SWRC attributed to the weakening of the ink-bottle effect during soil compression.