Study Of Coupling Numerical Simulation Of Saturated-Unsaturated Soil Under Rainfall Conditions

The stability of the slope is determined by its internal and external factors. The internal factors of the slope are inherent, and the external factors mainly include earthquake, rainfall events, and human excavation. The slope failure occurred frequently because of rainfall events in recent years. As a result, a systemic study on shallow water flow over porous soil is of great importance both in theory and application to engineering.The rule about water flow in the unsaturated soil and the soil-water characteristic curve are described in this thesis In the first time step during the numerical simulation, the permeability coefficient is calculated according to the initial water content of the unsaturated soil, because of as shown in the soil-water characteristic curve has the hysteresis phenomenon.A saturated-unsaturated FEM seepage analysis program is developed based on the Richards equation. Some examples are given to show the validity of the program. A method to calculate the discharge is developed and more accurate than traditional method.The infiltration process of the water on the surface is analysized under rainfall conditions, the two-dimensional mathematical model and its boundary conditions are presented. Some examples are given to explain the rules of unsaturated soil infiltration.The slope runoff FEM analysis program is developed based on the Saint-venant equations. The numerical solutions are compared with the analytical solutions and the experiment data and the characteristic line method solutions, the result validate of the program.The coupling analysis program of surface flow and subsurface flow over porous media is developed based on the conversion principles of water on the surface under rainfall conditions. A new method to judge the saturation of the surface is proposed in this thesis, the convergence is speeded up and the CPU time is saved by using this method.Five parameters are studied .namely rainfall intensity, initial water content, vertical saturated hydraulic conductivities, porosity and the ratio of the vertical and the horizontal saturated hydraulic conductivities by using the coupling program, the______________________________________________Abstract_____________________________________________results show the validity of the traditional infiltration theory.The alteration procedure of the underground water level is simulated under drizzle and storm rainfall conditions respectively adopting the coupling FEM analysis program of surface flow and subsurface flow . The numerical simulation of the underground water level shows that the drain ditch installed over the slope does not have an notable effect on the underground water level.