Analyzing landslide-induced debris flow and flow-bridge interaction by using a hybrid model of depth-averaged model and discrete element method

The Minbaklu Bridge, an essential segment of the southern cross-island expressway in Taiwan, was destroyed owing to debris flow in the Yusui Stream. To elucidate the development of debris flow in the Yusui Stream and the bridge collapse event, this study proposed a hybrid model of the discrete element method and depth-averaged model to simulate the event through three stages: formation of the natural dam, debris flow triggered by dam braking, and bridge collapse owing to the debris flow. The simulation results obtained indicate that the proposed model can provide reasonable simulations of the formation of natural dam in both time line and spatial distribution. Further, it indicated that the erosion developed at the river bed of the flow region, and illustrated the failure process of the Minbaklu Bridge, which revealed that it was uplifted before being pushed away. Furthermore, the final deposition of the alluvial fan deposition was demonstrated as well. Overall, the proposed hybrid model provides a useful tool for investigating debris flow and interaction with engineering structures.