Abstract: In the simulation of rainfall infiltration, current studies cannot realize the real-time conversion between the flow boundary and pressure boundary so as to accurately capture the groundwater movement characteristics under complicated rainfall conditions. Based on the saturated-unsaturated seepage theory, the difference between the rainfall recharge flow and actual infiltration flow on the boundary was used as a new judgment condition to distinguish the flow and pressure boundaries. The governing equation of dynamic transformation for the rainfall boundary in the single permeability medium was modified. Furthermore, the treatment method and governing equation were proposed to deal with the rainfall boundary in double permeability media. Numerical experiments and field application were conducted to verify and demonstrate the robustness of the newly proposed approaches. The simulation results suggest that the improved governing equation of dynamic transformation regarding rainfall boundary overcomes the limitations of traditional rainfall boundary processing methods, and can accurately realize the dynamic and real-time conversion between flow boundary and pressure boundary. The simulation results of rainfall infiltration on an in-situ slope illustrate the correctness and engineering applicability of the improved rainfall boundary.

Key words: rainfall boundary, bidirectional dynamic real-time conversion, single permeable medium, double permeable medium