SPH-based numerical simulation of catastrophic debris flows after the 2008 Wenchuan earthquake

Post-earthquake debris flows that have occurred in Sichuan Province in southwestern China following the Wenchuan earthquake on May 12, 2008, have caused significant damage and casualties. Previous earthquake-induced landslides produced large amounts of loose material that remained on the steep slopes and in the gullies. As a consequence of heavy rainstorms during the rainy seasons, the existing loose material was transformed into numerous debris flows. Research has shown that the debris flows in the Wenchuan earthquake disaster areas have been characterized by their large scale, high speed, long run-out, and destructive impact. In order to identify the areas potentially at risk and to predict the flow severity, an accurate numerical method is needed to simulate these debris flows. In this paper, we have proposed a smoothed particle hydrodynamics (SPH) modeling technique-a meshfree particle method-to simulate the post-earthquake debris flows in the Wenchuan earthquake disaster areas. The SPH modeling technique introduces a Bingham model to analyze the relationship between material stress rates and particle motion velocity. Compared to traditional numerical methods, the SPH modeling technique is a true meshfree method of a pure Lagrangian nature. It can instantaneously track the motion of each particle, accurately predict the velocity, and naturally handle problems with extremely large deformations. In addition, the SPH method is based on continuum mechanics, and is therefore an efficient method to simulate large-scale debris flows. In this work, first, a viscoplastic fluid was simulated and verified with experimental results in order to evaluate the accuracy of the SPH model. Then propagation analysis of two typical post-earthquake debris flows in earthquake-hit areas was carried out, applying the SPH model. The simulation results showed good agreement with the limited field observation data. Our proposed SPH numerical modeling is able to capture the fundamental dynamic behavior of post-earthquake debris flows and can partially explain these complex phenomena. These simulation results can provide a preliminary scientific basis for hazard assessment and site selection for reconstruction in earthquake-prone areas.