Threshold of Slope Instability Induced by Rainfall and Lateral Flow

In this study, a two-dimensional numerical landslide model was developed to investigate the effects of the amount of rainfall and lateral flow on induced slope failures. The Richard’s equation was used to evaluate pore water pressure distribution in response to moisture content variations induced by rainfall and infiltration in soil mass. The slope stability was then assessed using the limit equilibrium method of slices, and the moment equilibrium was considered. Several hypothetical cases involving various rainfall amounts and durations were simulated using the proposed model to investigate the possible tendency toward slope instability caused by rainfall time-series processes. After the rainfall conditions were analyzed, rainfall patterns were categorized as uniform, intermediate, advanced, and delayed types. Furthermore, the lateral flows running through the upstream and downstream boundaries of a slope were analyzed to investigate the lateral effects on the hillslope. The results indicated that the lateral flow may increase or reduce the groundwater table and, thus, accelerate or reduce the occurrence of slope failure. In addition, several rainfall threshold curves that accounted for the rainfall amounts, durations, and patterns were developed and appeared more realistic and to approximate real conditions more accurately than those created using one-dimensional landslide modeling do.