Effects of groundwater table position, soil strength properties and rainfall on instability of earthquake-triggered landslides

Although earthquake-triggered deep landslides are widely studied, less attention has been focused on the combined effects of groundwater table position, soil strength properties and rainfall on the instability of landslides triggered by earthquakes during rainfall events. In this study, to provide a better understanding of the conditions leading to catastrophic landslides, the effects of these factors on the instability of a homogeneous soil slope under different earthquake conditions are investigated through a series of sensitivity analyses. These analyses are based on a newly developed combined hydrology and slope stability model. The results show that groundwater table position, soil friction, soil cohesion, rainfall intensity and rainfall accumulation have significant effects on the instability of landslides. Groundwater table position and soil strength properties are found to be the primary factors controlling the instability of landslides, while rainfall accumulation plays a secondary role. On the other hand it is shown that increasing soil saturation, which is a direct effect of rainfall accumulation, decreases the factor of safety. The results also show the combined effect of rainfall duration and earthquake acceleration on the landslide instability. Specifically, for a given rainfall accumulation, there exists a threshold earthquake acceleration coefficient that would trigger a landslide; for higher rainfall accumulations, landslides can be triggered by earthquakes with smaller acceleration coefficients.