Numerical investigation of post-earthquake rainfall-induced slope instability considering strain-softening effect of soils

Although rainfall and earthquake have been widely recognized as the two most important factors for landslide, the failure mechanisms of a soil slope under the two natural disaster factors are totally different, thus it is still challenging to answer what will be the response of the soil slope under some extreme conditions of the individual factor or the combination ones. In this paper, we present a novel numerical investigation of the combined effect of earthquake and rainfall on slope instability. The deformation responses of a soil slope under different conditions of earthquake, rainfall and post-earthquake rainfall are analyzed using FLAC3D with user-defined sub-routines for defining the strain-softening behavior of the soil. The Mualem's seepage model is adopted for rainfall infiltration and slope deformation analysis. The numerical results indicate that the strain-softening behavior of the soil will significantly influence the seismic slope displacement caused by the earthquake ground motion. Considering extreme cases of rainfall after a short period of earthquake-induced slope deformation with local strain-softening, the combined effects take different forms of accumulating the ultimate slope displacement. The post-earthquake rainfall infiltration will make the seismically disturbed slope to be deteriorated further of the shear strength, and ultimately a landslide develops over time. It is anticipated that the findings from this study could provide reference value for understanding the landslide mechanism of soil slopes under the combined effect of earthquake and post-earthquake rainfall in order to plan for rationale disaster prevention measurements.