Analytic solution to coupled seepage in layered unsaturated soils

Layered soil such as landfill and cracked soils are often found in engineering. Its coupled infiltration and deformation during rainfall is significant for development of unsaturated soil mechanics. Based on fluid mass conservation, Darcy's law, and the constitutive model proposed by Lloret et al., coupled governing equations for seepage and deformation in unsaturated soils are obtained. The unsaturated coefficient of permeability is expressed using Gardner's model and the water retention characteristics are expressed using Boltzman's model. The analytic solution to the coupled equation is developed by Laplace transformation. The analytic solution and parameter analysis results show that the effect of coupling between unsaturated seepage and deformation is related with time. The modulus related to suction changes F has a marked effect on the pore water pressure. The larger the F ratio values for two-layer soils are, the more slowly the suction dissipates. The results indicate that a large F for the top-layer soil can effectively reduce the coupling effect. Volumetric moisture content changes in two-layer soils play a limited role in the suction distribution.