Abstract: The authors employ data research, theoretical analysis, and numerical simulation to develop a formula for calculating evacuation speed within spiral tunnels and a prediction method for evacuation time in high-altitude regions. They also examine how geometric parameters of cross-channels influence evacuation speeds in spiral tunnels under varying wind conditions, providing recommendations for cross-channel design to ensure safe evacuation. The research findings highlight the following: (1) Panic psychology, fire smoke, tunnel illumination, slope, and altitude significantly affect evacuation speed. A method is established for calculating evacuation speeds in spiral tunnels with steep longitudinal slopes in highaltitude areas, incorporating these factors. (2) A theoretical evacuation model is proposed for spiral tunnels under both congested and non-congested conditions. This model considers the worst-case scenario of a fire occurring at the entrance of a vehicular cross-passage, integrating the concept of zonal evacuation. (3) A performance-based analysis clarifies the impact of cross-channel geometric parameters on evacuation time, accounting for the specific evacuation characteristics of external traffic tunnels in hydropower projects. This analysis leads to recommended cross-channel design parameters suitable for various ventilation wind speeds.

Key words: highway tunnels, spiral tunnels, pedestrian crossing design, hydroelectric engineering, gradient, curve radius