Three dimensional numerical analysis of bridge foundation due to riverbed erosion

Taiwan is located between Eurasian plate and Philippines plate. Its geology is fragile. The geology structure belongs to a weak geology. There are many typhoons and downpour in Taiwan. The heavy rainfall often causes soil loss or slope failure. Debris flow occurs frequently in Taiwan during the typhoon season. That the fluid pressure flow coming with the impact of the huge rocks and floating lumber was brought by debris may contribute to the severe damage of structures of bridges. Therefore, it is the current urgent subject to establish the good procedure in order to seal bridge and eventually to guard against the personnel casualty. This research uses finite element method (FEM) Plaxis 3D Foundation as a tool to simulate analysis the foundation in bridge pier by debris-flow ruin. The flood level and the speed of flow in the different frequency year become very important analysis factors under the different scour depth to estimate the deformation, the inclination angle of pile and the whole bridge safety coefficient. The correlation between FEM calculation and observation to identify the usefulness of analysis model is confirmed, then to establish failure mechanism and safety evaluation.