Analytical solution of transient seepage problem in unsaturated soil based on principle of homogeneous construction

Unsaturated seepage phenomenon exists widely on the earth's surface, which has important value in many geotechnical engineering practices. The Richards equation describing unsaturated seepage and the corresponding definite conditions are linearized and dimensionless by using the Gardner exponential soil-water characteristic curve and the permeability function. Then, based on the principle of homogeneous construction, the linear dimensionless seepage governing equation is equivalently decomposed, and the separation variable technique is used for analytical calculation. The analytical expressions for the dimensionless permeability coefficient, seepage rate, volumetric water content and matric suction head are obtained. Two typical soil layers are selected as the research objects to analyze the seepage evolution laws under the sudden increase of surface infiltration rate. The results show that the movement speed of wetting front to the depth of soil layer decreases gradually with time. The saturated permeability coefficient of coarse-grained soil has a significant effect on the development of unsaturated seepage from steady state to re-steady one. The closer to the surface, the shorter the time required for the seepage velocity to increase to the steady state; the farther away from the surface, the later the response time of infiltration rate to the surface boundary. The vertical distribution of matric suction head and volumetric water content depends only on the boundary conditions.