Non-dimensional parameters controlling occurrence and characteristic of landslides that provide sediment for debris flow development

Abstract

Landslides are one of the most important processes supplying debris flow materials into channels. We need to predict the timing, location, and volume of landslides for better estimation of the occurrence of debris flows. However, a number of soil parameters (e.g., the angle of internal friction, cohesion, and porosity), which have significant spatial variability, are needed to predict landslide occurrence. Therefore, it is important to make clear the contribution of these parameters to overall slope stability and their relationships to one another. In this study, we normalized the safety factor equation for infinite slope model, and introduced multi soil layer structure into the model. We also tried to clarify factors affecting the pore water pressure on the basis of the equations for the vertical infiltration process (i.e., continuity equation and Darcy’s law). Depth gradient of the pore-water pressure at the given soil layer is controlled by the ratio of the water velocity in saturated zone to the hydraulic conductivity at that layer. New, non-dimensional representations for the effects of groundwater table and cohesion of soil were obtained by the normalization of the safety factor equation. They are evaluated relative to each other by comparison to the stability of dry non-cohesive soil. The effect of the groundwater table and the cohesion of soil on the slope stability are both affected by depth of the sliding surface. We also found that the effect of cohesion should be evaluated from the comparison with the maximum effect of groundwater table to the stability. This can explain the immunity of post- landslide slopes to immediately subsequent landslides, as well as the cyclical nature of landslide processes.