Optimization design and numerical simulation of cross-passage intersection angles in high-altitude super-long tunnels

The orientation of cross-passages is a critical factor for both construction safety and operational efficiency in high-altitude, extra-long tunnels. Currently, systematic theoretical support is lacking for the optimization of cross-passages under complex geological conditions and unique ventilation environments in high-altitude regions. For solving these problems, this research puts forward a "bell-mouthed ("Ba-zi")" arrangement-for intersecting passages, which has an optimized intersection angle θ. Through combining ventilation efficiency, expenditure and mechanical reaction, this research adopts the united fluid dynamics and rock mechanics digital simulation frame to investigate the behavior of the tunnel in five cross-passage angle situations (30°,40°,60°,70°, and 90°), and systematically makes comparison on the comprehensive performance of the tunnel under different cross-passage angles. The 60° configuration effectively mitigates localized stress concentrations within the "triangular zone" and substantially curbs surrounding rock deformation. Furthermore, from an aerodynamic standpoint, the 60° further optimizes the flow field, yielding the minimum local resistance coefficient, suppresses vortex formation and mitigates gas stagnation zones, facilitating a synergistic alignment of structural integrity, ventilation efficiency, and economic viability. The study establishes a rigorous theoretical framework and offers quantifiable benchmarks for the geometric design of cross-passages in super-long plateau tunnels.