Abstract
An accurate investigation of the landslide dam breach process is crucial for the understanding the breach mechanism and disaster prediction. However, the numerical research on the landslide dam breach process to date is rarely reported, especially regarding the soil-water flow coupling effect incorporated in the erosion process. This paper presents a numerical investigation on the longitudinal breach process of landslide dams via a coupled discrete element method (DEM) and computational fluid dynamics (CFD) with the volume of fluid (VOF). Moreover, a virtual sphere model is proposed to overcome the computational instability caused by the particle size approaching the mesh size. The accuracy and validity of the improved coupled method are verified using a series of single particle sedimentation cases. By employing this method, the longitudinal breach process of landslide dams featuring different materials and hydrodynamic conditions has been simulated. It is found to satisfactorily reproduce the longitudinal breach process of landslide dams including surface flow erosion, backward erosion, head-cut erosion, and water and sediment rebalance or complete breach. The effects of the inflow discharges and dam materials on the erosion process are systematically resolved. The breach flow can cause the rotation trend of particles and lead to the increase of tangential contact force at the initial stage of the dam breaching. During the breach process, both the strength and density of the force chain continue to attenuate. The results obtained from the improved coupled DEM-CFD simulations can reasonably explain the particle-fluid interaction mechanisms, physical and morphological evolution and breach process at both macroscopic and mesoscopic scales.
Highlights
Landslide dams, presented as natural dams formed by landslides blocking the river channels, are widely distributed in mountainous regions all over the world (Schuster and Costa, 1986; Korup, 2004; Nian et al, 2018)
As a natural dam without a spillway to control the reservoir capacity of the barrier lake, it Simulation of Landslide Dam Breach has a high risk of failure that may cause outburst floods with potentially catastrophic consequences in downstream areas (Casagli et al, 2003; Chang et al, 2011; Wu et al, 2020)
A coupled discrete element method (DEM) and computational fluid dynamics (CFD) with the volume of fluid (VOF) was used to model the longitudinal breach process of landslide dams, and a virtual sphere was proposed to overcome the computational convergence caused by the limitation of particle and mesh cell size
Summary
Landslide dams, presented as natural dams formed by landslides blocking the river channels, are widely distributed in mountainous regions all over the world (Schuster and Costa, 1986; Korup, 2004; Nian et al, 2018). This article aims to provide new insights of the breach mechanism of landslide dams through numerical simulation To achieve this goal, a coupled discrete element method (DEM) and computational fluid dynamics (CFD) with the volume of fluid (VOF) was used to model the longitudinal breach process of landslide dams, and a virtual sphere was proposed to overcome the computational convergence caused by the limitation of particle and mesh cell size. An improved coupled DEM-CFD method is developed to simulate the longitudinal breach process of landslide dams, and a virtual sphere model is proposed as a new local porosity calculation method to overcome the limitation of the particle and mesh cell size. Under the same inflow conditions, the residual dam height of the wide size range fine-grained dam material is always lower than that of the unsize coarse-grained dam material, which indicates that the existence of fine particles reduces the erosion resistance of the landslide dam. This explains the phenomenon that there are still residues in scenario C4 and the dam body has completely failed in scenario F4
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