Rainfall-induced landslide simulation via a coupled FVM-DEM method

Abstract

Background: Rainfall-induced landslides in granite residual soil are a growing concern due to their water sensitivity and complex failure mechanisms. Existing numerical approaches either oversimplify infiltration effects or fail to capture particle-scale responses. Therefore, there is a pressing need for a novel method capable of reproducing the entire failure process of rainfall-induced landslides. Methods: This study developed a coupled finite volume and discrete element (FVM-DEM) framework to simulate both unsaturated seepage and soil mechanical behaviour. Transient infiltration was governed by the Richards equation, while particle interactions were represented using a contact-bond model. Moreover, a radial basis function was employed to map water content from the FVM grid to DEM particles, allowing dynamic updates of strength parameters. Results: The proposed FVM–DEM framework captured the spatiotemporal evolution of rainfall infiltration and its influence on soil strength degradation. Simulations conducted under three rainfall intensities demonstrated that increasing water content caused progressive bond breakage and a consequent reduction in shear strength, thereby leading to slope failure. With increasing rainfall intensity, the time to failure decreased from 5.0 h at 10 mm/d to 3.4 h at 50 mm/d and 1.6 h at 100 mm/d, accompanied by a rise in bond breakage proportion from 16.81% to 21.07% and 27.41%, respectively. A stability index based on energy variation was adopted to identify the onset of failure. Stronger rainfall results in greater changes in gravitational potential energy, leading to a greater threshold for the index. Conclusion: The proposed method successfully reproduced the full failure process from infiltration to failure stage, providing insights into the evolution of both macroscopic deformation and mesoscopic contact degradation.