| Summary: | 碩士 === 國立交通大學 === 土木工程學系 === 100 === The formation of a landslide dam depends on the conditions of the river hydrological characteristics and the run-out features of the slope mass; these conditions are related to hydrology, geology (including lithology and geologic structures) and morphology. Susceptibility analyses of landslide-dam formation aim to locate possible sites for landslide dams to occur; in general, these analyses made use of statistical method based on recorded landslide dam cases. However, the relevant data for statistics are often insufficient. It is neither possible to conduct full-size model test to explore the run-out process of unstable mass. This thesis attempts to investigate some important factors for the run-out behavior of landslide/avalanche masses by numerical simulation, and to examine the chance for a run-out mass to block the river valley so that forms a landslide dam. This study adopts the code of particle flow simulation PFC3D to model the run-out process of rock masses on slope along with a landslide or avalanche. Reconstructions by simulation for several real landslide-dam cases were conducted to verify the simulation approach. The validation demonstrates that the formation process of a large-scale landslide dam can be correctly modeled with appropriate assigned parameters. For a landslide-dam case without sufficient data or records, it is then possible to apply this approach to reconstruct what could have taken place. This study assumed a series of virtual conditions to explore a few variables that may determine whether a landslide-dam can be formed. The results indicate a few interesting trends. As the volume of the landslide is less than 100,000 m3, the final deposition tends not to block a river. Next, for a low elevation drop (from the landslide spot to the river base), the deposition after the run out of landslide tends to be more confined (not spreading out) in the river valley adjacent to the toe of the landslide slope. As a result, the dam width along the flow direction will be limited and prone to piping or slope failure very quickly. The simulation approach in the study should be applicable for further susceptibility study of landslide-dam formation.
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