Abstract: The void ratio of soil has an important influence on the soil-water characteristic curve (SWCC) of unsaturated soil. Experimental studies have shown that pores expand or contract under different hydraulic load paths, which results in the hysteresis of the soil-water characteristic curve (SWCC). Based on this finding, this paper assumes that the expansion and contraction of pores can cause the hysteresis of the soil-water characteristic curve (SWCC). In this study, axial translation technique is employed as an example to explain the expansion and contraction of soil pores under hydraulic loading. Then, an incremental equation for the soil-water characteristic curve that can describe the hysteresis is derived. In this equation, expansion and contraction of pores are calculated by assuming ?d to be a constant and combining the redefined equivalent pore radius with the Fredlund-Xing equation. The proposed soil-water characteristic curve model can be used to predict other scanning curves by simply using the model parameters obtained from the main drying curve and an arbitrary scanning curve. Finally, the applicability of the proposed model to different soil types is verified using five data sets obtained from tests. It is also shown that the proposed model is capable of predicting high-order scanning curves.

Key words: unsaturated soil, soil-water characteristic curve, hysteresis effect, scanning curve, pore expansion and contraction