The influence of pore gas pressure and gas permeability on rainfall infiltration

Rainfall infiltration is a significant trigger that lead to slope failures. The change of pore gas pressure caused by rainfall infiltration plays an important role in the slope stability. The purpose of this research is to examine the important effect of the pore gas and the gas permeability in the process of rainfall infiltration. Firstly, Water-air-two phase flow analysis were adopted as to analyze the movement of water and gas in the process of rainfall infiltration. In order  to evaluate stability of slope, the pore gas pressure could be considered as a external load variable to incorporate in the thrust residual method which is a traditional method to evaluate slope stability. The result showed that safety factor decreased over the time when adding pore gas pressure into slope stability method compared to not consider the gas pressure, this is mainly because the pore gas pressure gradient was formed and the pore gas pressure is an important factor in the infiltration of slope stability. In addition, a numerical soil column model with the finite element method has been established for examining the effects of pore gas pressure and gas boundary condition on the rainfall infiltration. After giving the same initial conditions, the soil column under various gas permeable conditions is simulated then the influence of gas boundary permeability on infiltration intensity, pore gas pressure were also analyzed. The result showed that there is a highly relevant relationship between infiltration intensity and gas permeability on the boundary. The stable infiltration intensity is sensitive and it decreases quickly when the gas boundary permeability is at lower stage. As gas boundary permeability going up, this sensibility is declined gradually. The relationship between the infiltration intensity and gas boundary permeability can be regressed to be logarithmic. Furthermore, with the increase of gas boundary permeability, the pore gas pressure increases nonlinearly and the movement  of wetting front slows down.