Risk coupling effects on flood-induced hazards in urban underground spaces

Flooding events are critical issues impacting the safety of urban underground spaces. In the previous research, there is a lack of identification and coupling analysis on the risk of urban underground space induced by flooding. This work identifies risk factors and coupling risk types by analyzing 63 cases of flood-induced accidents with serious consequences in urban underground spaces. The hierarchical structure of risk factors is determined based on the Interpretative Structural Modeling Method (ISM). Then, the risk coupling degree value of each coupling types are calculated by an analysis method based on N-K model and Bayesian Network (BN). It is found that the risk coupling degree value generally increases with the increase of the number of risk factors involved in the risk coupling. Among these, the R-W-H-G risk coupling degree value is the highest, followed by the risk involving both W and G, with the R-only double-factor risk being the lowest. The involvement of material condition factors (W) and management factors (G) in risk coupling leads to a higher accident risk. The change characteristics of the coupling degree for each risk coupling types are analyzed by quantitatively adjusting the state of the coupling risks. Results show that when the state of management factor (G) changes, the coupling degree of related coupling risk changes significantly. Human factors (R) are prone to participate in the coupling when at least two other risk factors are coupled, leading to a more severe risk coupling effect. Sensitivity analysis reveals that key risk factors are prone to cause the occurrence of risk coupling events, with g3 having the greatest impact on the coupling risks. All key risk factors tend to first trigger three-factor risk coupling, subsequently leading to the occurrence of four-factor risk coupling events, rather than directly inducing four-factor risk coupling. Finally, the risk management recommendations are presented. This study analyzed the key risk factors of urban underground space induced by flood, and explored the coupling effect of risk and the dynamic change characteristics of coupling risk. It provides a theoretical reference for the management and control of flood disaster risks in urban underground spaces, which helps to effectively prevent and mitigate secondary accidents in urban underground spaces caused by flooding.