Numerical and field experimental study of rainfall infiltration based on water-air two-phase flow

Rainfall infiltration is a water-air coupled flowing process which involves the surface runoff and slope seepage. In this paper, a coupled model of water air flowing process and surface runoff is presented to simulate the rainfall infiltration process in a soil slope. Based on the results of numerical simulation, regularity of surface runoff is analyzed by dividing the slope surface into two areas according to the flowing direction of total velocity of water and air. The area that water and air flow in is the 'inhalation zone' and that flow out is 'overflow zone'. The intersection line of two areas changes with the rainfall condition, slope geometry and permeability of slope soil. Water and air flowing process in the slope is presented and there are remarkable delaying effects of rainwater infiltration with the increasing of depth. Evaluation of pore air pressure in the slope is obtained and the amplification of pore air pressure by intermittent rainfall process is discussed based on the results. A field experiment is carried out to testify the water and air flowing regularities which draw from the numerical simulation. By monitoring the pore gas pressure and the water content of soil in the rainfall process, the phenomenon of retardation effects of pore gas on the infiltration and amplification effects of intermittent rainfall on the pore gas pressure can be observed in the natural rainfall progress.