Abstract: The soil-water characteristic curve shows hysteresis when boundary conditions such as temperature and water head change cyclically. To simulate the hydraulic properties of the unsaturated soil under temperature cycle, this paper proposes an empirical model to reflect the hysteresis effect. The model assumes that the curve shape of each scanning curve is similar to the corresponding boundary curve, therefore, using the equations of the two boundary curves, the model is capable of predicting all the scanning curves without introducing new parameters. In this paper, a soil column test using kaolin clay as the medium and dry-wet cyclic driven by temperature is designed. In the impermeable soil column, the water bath is used to make an end of the soil change temperature cyclically. The results show that the pore water will migrate from the high temperature to the low; after the temperature drops to the initial state, the distribution of water content will not completely return to the initial state, showing a hysteresis effect. Using the hysteresis model in numerical calculation can reflect the hysteresis in the water migration process in soil. The existing results of sand and silt also verify the effectiveness of the proposed model. This model is easily to calculating and programming, and is capable of being applied to engineering problems such as geological disposal, heating pipeline design.

Key words: cyclic temperature, unsaturated soil, soil-water characteristic curve, hysteresis model, thermo-hydro coupling