Based on flow theory of unsaturated soil

a model for moisture migration is set up to study steady flow subjected to vacuum preloading. Meanwhile the governing equation and the corresponding analytical solution of pore water pressure distribution are given. The model is first verified by in-situ measured data. Then parameters are analyzed. Results show that the calculated results agree well with the in-situ measured data. Both diffusion flux (Q) and unsaturated coefficient (?) have a marked effect on the formation position

indicating that they affect strength and thickness of unsaturated region. The larger diffusion flux is

the larger matrix suction of soil surface is and the greater variation trend of pore water pressure is. Unsaturated soil is seldom influenced by unsaturated coefficient ? when it is in range of 0.3-1.0 kPa-1.