Field and numerical investigations on triggering mechanism in typical rainfall-induced shallow landslides: a case study in the Ren River catchment, China

A combined field hydrological monitoring and hydro-mechanical numerical investigation into the triggering mechanism in rainfall-induced shallow landslides was proposed and carried out in the Ren River catchment of central China, considering the effect of predisposing geological conditions. Based on the seasonal monitored data of shallow soils, hydrological behaviors of the slope were obtained and it facilitates the development of conceptual hydrological models. A calibrated hydrological model was then obtained by comparing the event-based results of both the monitored and simulated variation in soil water content/pore pressure. Then, this calibrated hydrological model was extended to reconstruct a seasonal hydrological regime and the corresponding triggering condition of a shallow landslide on the monitored slope in 2010. Local geomorphological and stratigraphic features of the slopes affected by shallow landslides in the Ren River catchment were considered as prediposing factors to impact hydrological behaviors and the corresponding triggering mechanism of a shallow landslide. Additional slope cases with distinctive slope topography and stratigraphic features were reconstructed to carry out seasonal hydrological response modelling and local slope stability analysis. Results indicate that the decreasing matric suction in response to rainfall infiltration at shallow depth is the main trigger for those landslides on planar and concave slopes with relatively thick soil mantle. A stratigraphic discontinuity that the presence of a steep rock scrap leads to the pinching out of a soil layer on a convex slope, narrows the drainage channel and possibly leads to a significant accumulation of a perched water table. The infinite slope model, considering the evaluated pore pressure at different depths and local geological conditions can be effectively applied to reconstruct the shallow landslide occurrences during the rainstorm event in 2010.