Full-scale experimental study on evacuation behavior characteristics of underwater road tunnel with evacuation stairs under blocked conditions

•Experiments were conducted in a real underwater tunnel with evacuation stairs.•The alighting time of passengers from vehicles and influence factors were stated.•The average evacuation capacity of the stairs was 33.3 ± 4.1 person/min.•Reduced values for evacuation speed under blocked conditions were obtained. In recent decades, with the rapid development of the economy and tunnel construction technology, an increasing number of underwater road tunnels have been constructed in China. Underwater road tunnels play a crucial role in transportation hubs that connect cities and regions. Underwater tunnels have strong closures, which makes evacuation and rescue difficult. Therefore, personnel evacuation in emergencies, such as fires, has become a critical problem that needs to be solved. A full-scale evacuation experiment in an underwater shield tunnel with 188 participants was conducted to explore the characteristics of personnel evacuation behavior under the blocked condition of an underwater shield tunnel in the case of fire. The time of fire detection and personnel response, alighting time of passengers from vehicles, opening time of the stair-cover plate, evacuation capacity of stairs, and relationship between the evacuation speed and age and gender of participants were obtained. The experimental results showed that the driver’s actions had a strong demonstrative effect, and the improvement of the driver’s efficiency in handling emergencies could promote the evacuation process. The average alighting time per bus passenger was 1.41 ± 0.53 s, and proper personnel guidance, good road conditions, and increased tunnel familiarity reduced it. The average evacuation capacity of the stairs was 33.3 ± 4.1 person/min. When the proportion of older adults increased from 0 % to 10.64 %, the evacuation capacity of stairs decreased by approximately 8.5 %. The evacuation capacity of stairs can be significantly improved through reasonable organization and evacuation guidance. However, as the number of people gathered at the stair entrance gradually increased, the “bottleneck” effect became significant, and the evacuation capacity was primarily controlled by its structure at this time. The average evacuation speed for male and female was the same in good road conditions, about 1.39 m/s, but decreased significantly in blocked conditions, to 0.72 m/s and 0.48 m/s, respectively. Further, it decreased to 1.27 m/s and 1.23 m/s, respectively, in the secure channel, which may be rel