Abstract: The soil-water retention curve (SWRC) is one of the fundamental physical relationships for unsaturated soil. Experimental studies indicate that volume deformation not only alters the pore size distribution (PSD) of the soil but also significantly affects the heterogeneity (or non-uniformity) of pore structure. Based on the inherent relationship among the three phases of soil, a calculation formula considering the influence of volume deformation on soil saturation under constant suction is proposed. In terms of hydraulic hysteresis, the ink-bottle effect is employed to reveal the impact of volume deformation on the hysteresis characteristics of SWRC. Assuming that, given the initial void ratio, the increase in suction is mainly consumed in changing the soil saturation and overcoming the ink-bottle effect, a heterogeneity factor representing changes in pore structure is introduced into the VG model. This heterogeneity factor reflects the influence of volume deformation on the evolution of pore structure, thereby constructing a SWRC model that considers the coupling of hydraulic hysteresis and deformation effects. The proposed SWRC model not only captures the impact of volume deformation on SWRC but also explains the physical mechanism underlying the evolution of hysteresis loops with changing void ratio. Finally, the proposed model is validated using eleven sets of experimental data. The results indicate that the proposed model effectively describes the influence of soil deformation on SWRC boundary curves and hysteresis loop evolution.

Key words: unsaturated soil, water retention, hydro-mechanical coupling, hydraulic hysteresis