Risk Assessment of Metro Tunnel Evacuation in Devastating Urban Flooding Events

Due to the increased frequency and magnitude of urban flooding events, there is an urgent need to study evacuation safety and disaster risk reduction in inundated urban underground spaces. In the literature, there is still a lack of methodologies to assess flooding risk in urban underground areas, which can account for the mutual effects of hydrodynamic characteristics, fluid-human interactions, and human behaviors. This study presents a hybrid model to investigate flood-induced evacuation safety in a metro tunnel based on the coupling of the hydrodynamic module, the human instability module, and the human behavior module. Firstly, floodwater conditions and flow characteristics are calculated by the hydrodynamic module. It is found that evacuation speed decreases with an increase in flow velocity and water depth. The water depth obviously increases after the flow passes the train where the flow velocity decreases with an increase in pressure due to the inference of the obstacle. Secondly, both depth-averaged velocity and depth of floodwater are used as the input parameters for the behavior module and stability module, and the flood hazard regimes for children and adults are then determined in an inundated metro tunnel. The relatively safe evacuation moving speeds for a child and an adult is suggested to be less than 0.5 m/s and 0.6 m/s, respectively. This study provides a novel approach to predicting the evacuation process and supports an early warning system in flood-prone underground areas for sustainable cities.