3D numerical modeling using smoothed particle hydrodynamics of flow-like landslide propagation triggered by the 2008 Wenchuan earthquake

The extremely strong Wenchuan earthquake triggered thousands of landslides in Sichuan Province, China. Flow-like landslides, such as the Tangjiashan, Wangjiayan, and Donghekou landslides were among the most destructive, causing many casualties and serious economic damage. It is therefore important to identify the flow mechanisms and investigate the specific characteristics of these flow-like landslides. This paper presents a three-dimensional model based on smoothed particle hydrodynamics (SPH) to simulate rapid landslide motion across 3D terrain. The Navier-Stokes equations in a CFD framework are used as governing equations, and artificial viscosity is incorporated into the pressure terms in the momentum equation to dissipate energy to avoid numerical oscillation and particle penetration, thus improving the stability of the numerical results. A non-Newtonian fluid model, the Bingham model, has proven suitable for describing the relationship between the shear strain rate and the shear stress in highly deformed soil materials. In the proposed model it is used as the constitutive model to describe the fluidization characteristics of flow-like landslides combined with the Mohr-Coulomb yield criterion. The model incorporates a no-slip boundary condition, to consider the effect of a solid boundary on slope movement. Ghost particles are created and assigned an artificial velocity. The viscous force caused by the solid boundary is calculated using the relative velocities between the fluid and the boundary particles. Open Multiprocessing (OpenMP), an API for multi-platform shared-memory parallel programming, is used to improve the efficiency of the SPH code running. To show the validity of the proposed approach, a benchmark problem of 3D dam break was simulated. The calculated distances of the surge front at different times agree well with the test results. Numerical modeling of the propagation of the Tangjiashan, Wangjiayan, and Donghekou landslides was performed by the application of SPH models to real flow-like landslides. The whole flow processes of these flow-like landslides across the 3D terrain are represented. The landslides change direction, split or join in, and spread or contract in their flow path in response to the local topography. Time-history curves of the velocity and displacement were obtained to analyze the movement characteristics of the landslide mass. The shapes of the deposition zones after slide occurrence were investigated. Comparisons of the SPH simulated geometry and the surveyed landslide configurations for the Tangjiashan, Wangjiayan and Donghekou landslides were conducted, and show a high degree of similarity. This indicates that the proposed 3D SPH model can accurately represent the evolution of the final slide shape. The prediction of the fluidization characteristics of earthquake-induced flow-like landslides can notably reduce sudden loss of life, as it provides a means for mapping hazardous areas, for estimating the hazard intensity, and for identification and design of appropriate protective measures.