Abstract: In recent years, frequent extreme rainstorms cause flooding in urban tunnels. To address this problem, the authors summarize the causes of flooding disasters and the existing antiflooding experiences in urban tunnels based on relevant global literature and news reports. The current policies, standards, and contents of antiflooding work in major cities across China during the operation stage of urban tunnels are analyzed. Consequently, antiflooding measures for urban tunnels are examined. The antiflooding measures are classified into six major systems: (1) a barrier system to enhance the flood prevention capacity at tunnel exits, (2) a diversion system to divert water outside the tunnel in advance, (3) a drainage system to ensure that the drainage system inside the tunnel functions smoothly and meets the drainage requirements in the highstandard rainfall return period, (4) a control system to ensure the normal operation of the power supply and control system for the tunnel drainage system, (5) a warning system to prevent flooding in advance by increasing the flood-warning devices inside and outside the tunnel, and (6) an emergency system that can ensure timely emergency support measures in flooding accidents. Based on the maintenance grade of the urban tunnels and the flood risk grade within the tunnel site, antiflooding grades of urban tunnels can be classified into Grades Ⅰ, Ⅱ, and Ⅲ. Based on this classification, the upgrading schemes of the existing urban tunnels and the design of the planned tunnels can be determined.

Key words: urban tunnel, flood prevention measures, flood prevention upgrade, flood-prevention grading, systematic flood control