Enhancing resilience of urban underground space under floods: Current status and future directions

Urban underground space (UUS) has become an integral component of modern cities. However, its vulnerability to inundation results in flood disasters occurring in UUS worldwide every year, posing significant threats to human lives and property. Hence, enhancing the resilience of UUS under floods has become a widely recognized consensus in both engineering and academic communities. To gain a better understanding of flood issues of UUS, this paper conducts a systematic review to present the current status of flood control in UUS and discuss some future research and practice directions. Firstly, an analysis of the causes of UUS floods and their characteristics compared with aboveground floods is provided. Subsequently, detailed introductions are presented on three lines of flood defense for UUS in engineering practice, including the elevation design of entrances, flood barriers, and drainage systems. Special attention is given to five research hotspots aiming to enhance UUS's flood resilience: (1) flood process modeling, (2) flood risk assessment, (3) crowd emergency evacuation, (4) flood vulnerability and recoverability of underground transport network, and (5) flood resilience analysis. Finally, three critical directions for future research and practice, including constructing sponge underground space, adopting advanced information technologies, and adapting UUS to climate change, are proposed in order to further advance the conceptual and technological developments in UUS inundation prevention.