Abstract: In traditional research on SWCC model, only the capillary component of soil matrix potential was taken into consideration, while the adsorption component was ignored, which makes it overestimate the matric suction in the low saturation range. In view of this, the soil pore system is assumed to be represented by a cluster of capillaries with pore throats with the pore size distribution obeying the fractal power law. On this basis, the water movement in soil can be divided into two stages, i.e., capillary water and adsorbed water both participate in water movement, and only adsorbed water participates in water movement. The SWCC model reflecting soil’s water holding capacity and the hysteresis effect in the whole range of matric suction is derived.By existing test data and research results,the present constitutive model is verified to be rational and feasible with the predicted curve agreeing well with test data,and capable of better reflecting the water holding capacity of unsaturated soil than existing methods.

Key words: unsaturated soil, fractal theory, SWCC, capillary model, hysteresis effect, adsorbed water