Energy-based coupling risk assessment (CRA) model for urban underground utility tunnels

•Energy transfer and conversion could be a novel pattern for risk assessment.•Coupling risk assessment framework for utility tunnels is proposed.•Risk assessment of typical coupling accidents in utility tunnels is conducted.•The relation between coupling effect, synergistic effect, and cascading effect is distinguished. As a kind of highly integrated urban critical infrastructure, the urban underground utility tunnel hosts various pipelines to facilitate the city life. But the integration of hazardous pipelines like natural gas pipelines and electric cables inside a confined infrastructure also brings emerging risks due to coupling effect, which have not been systematically analysed by the existing method. So, there is an essential need for a coupling risk assessment (CRA) model to tackle coupling effects and corresponding coupling accidents in utility tunnels quantitatively. A clear definition and classification of coupling effect, synergistic effect, and cascading effect are proposed in this work. By introducing the energy transfer and out-of-control theory, it is feasible to identify interacted hazards systematically and coupling accidents in utility tunnels. Natural gas explosion, cable fire, and rain-triggered ponding are identified as typical coupling accidents to perform CRA. The results indicate that the risks of the 3 coupling accidents are considerable, and fatality is possible in the case of gas explosion and ponding. It can be concluded that the current firefighting systems and drainage systems are not sufficient for risk mitigation of utility tunnels with coupling effect.