Abstract: A constitutive model with the double-scale pore structure from macroscopic and microscopic views is proposed for predicting the capillary hysteresis and mechanical behaviours of unsaturated expansive soils based on the BExM and the existing hydro-mechanical models for unsaturated non-expansive soils. The proposed model takes into consideration two factors the interaction between the micro- and macro-structure of expansive soils, and the fully coupled capillary hysteresis with mechanical behaviours. The predictions are performed on the cyclical controlled-suction test results published in public. The comparisons between the measured and predicted results indicate that the proposed model can quantitatively predict the capillary and mechanical behaviours of unsaturated expansive soils.