Investigation of the initiation of shallow failure in widely graded loose soil slopes considering interstitial flow and surface runoff

Wide-grade loose soils (WGLS) are common source materials for denuding hillslopes, mobilizing sediments, and causing geo-hazards. Although the effects of interstitial flow process on the shallow failure of WGLS materials are widely studied during rainfall, the combined effects of interstitial flow and surface runoff processes remain poorly understood. This in turn limits our ability to better understand the effects of fluid flow on the mechanical response of hillslope soils. In this study, flume model test was performed under rainfall infiltration and surface runoff conditions to further study the initiation process of WGLS failure. Based on the experimental results, a new mathematical model was then explored by incorporating hydrodynamic theory considering the surface runoff and fine particle migration effect. Experimental results shown that no significant slope failure was triggered only under the rainfall infiltration condition, but the slope materials could transform into continuous surface erosion under the thin surface runoff condition. Meanwhile, the back calculations and analyses of the mathematical model shown that the established model here proved to be better suited for describing WGLS failure.