Numerical Analysis of Seepage for Saturated-Unsaturated Pavement Structure Under Rainfall Conditions

The paper aims to analyse the seepage characteristics of saturated-unsaturated subgrade and pavement under designed rainfall condition by the combination of experimental data tested from laboratory and numerical simulation through COMSOL Multiphysics, a commercial finite element software for multiphysics problems. At first, based on the general seepage theory, a partial differential equation (PDE) of seepage flow for saturated-unsaturated pavement is deduced by using the principle of effective stress and considering the impact of material compressibility. Using the PDE and the soil water characteristic curve (SWCC) presented by Van Genuchten, numerical examples for pavement structure are calculated with the software COMSOL Multiphysics, in which the change of rainfall intensities and different groundwater levels are taken into consideration. The resulted variation curves of saturation at different times demonstrate that, with the increase of the rainfall intensity, the time for subgrade and pavement to reach to be saturated is decreasing gradually. During the process of rainfall, the groundwater level has definite effect in the process of rainfall infiltration. The simulation methodology can be used and extended to the further research on mechanism of seepage of saturated-unsaturated pavement structure.