Computational investigation of landslide-water-sediment interaction and resultant flow dynamics through a mesh-free method

Abstract

Landslides are a type of geological disaster characterized by the sudden movement of sediment-liquid mixed materials, which have the potential to generate powerful tsunami waves in water bodies downstream. The resultant tsunami waves can result in catastrophic events by causing significant run-up and dam overtopping, subsequently leading to sediment bed erosion downstream. The whole process of the landslide-induced tsunami waves, along with the resultant wave overtopping and sediment bed erosion, is rarely researched. We presented a mesh-free Smoothed Particle Hydrodynamics (SPH) framework effectively representing the complex interactions between landslides and liquids, as well as capturing the generation and propagation of tsunami waves and the resultant overtopping process. The validations indicate that the presented SPH framework is capable of reproducing the complex interactions between landslides, sediments and liquids. The landslide sliding into the water can release significant energy, potentially causing severe tsunami waves that pose a threat downstream. We systematically investigated the relationship between landslide properties and induced tsunami wave characteristics, as well as the energy transfer between the landslide and waves. The results show that the effective landslide volume is the significant influential factor on the maximum wave height. The energy transfer analysis corroborates such a relationship and further finds an exponential relationship between the landslide potential energy reduction and maximum wave height. Building upon the investigation of landslide-induced tsunami waves, we further explore the overtopping waves that are induced by landslides. The results show that the maximum wave height, mean velocity, and safety factor exhibit an increasing trend with the increase in landslide position and initial water depth, as well as a decrease in the slope-to-dam distance. Regarding the influence of landslide size and density, the maximum wave height, mean velocity, and safety factor are found in the middle scenarios. Such a phenomenon can be attributed to the formation of a hole on the top of the landslide and the subsequent rebound, leading to severe energy dissipation. The slope has a significant effect on wave depth and mean velocity, while it has minimal impact on the safety factor. The prediction equations of the maximum overtopping wave height, safety factor, and individual overtopping volume were provided for the hydrodynamic response considering varying initial factors. Flow-driven sediment erosion exhibits multiphase characteristics and involves reversible solid-liquid mass exchange, wherein various rheological models and yield criteria are available, but their cooperative performance remains unclear. Here, six combinations of popular rheological models and yield criteria with varying physics are implemented and assessed based on four classical erosion experiments. The combination between Herschel-Bulkley-Papanastasiou rheological model and Mohr-Coulomb criterion best captures the erosion and waterfront. The model further reveals the velocity decreases exponentially and sediment concentration increases linearly before saturation concentration along with the depth in the movable sediment layer. Overall, this thesis provides a global perspective to understand the landslide-induced tsunami waves, along with the resultant wave overtopping and sediment bed erosion. The multiphase SPH framework presented in this thesis further improves the landslide theory, which can guide future research on landslide-induced tsunami waves.