Abstract:

To address the issue of excessive safety factor values and significant deviation from actual conditions in current gas classification standards for traffic tunnels, this study proposes replacing the conventional fixed value with the ratio of the maximum to average wind speed in the tunnel cross-section as a dynamic safety factor, thereby enhancing the accuracy of classification criteria. Utilizing numerical simulation methods, the ventilation flow fields of six traffic tunnels with varying cross-sectional areas under four steady return-air wind speed conditions were systematically analyzed, with a focus on the spatial distribution patterns of the wind speed safety factor and its correlation with cross-sectional area. The findings reveal that: (1) The flow field near the tunnel face exhibits pronounced non-uniformity, and the ventilation flow field can be categorized into three distinct zones—the vortex zone, transition zone, and stable zone. The wind speed safety factor demonstrates considerable variability in proximity to the vortex zone but gradually stabilizes with increasing distance; (2) Based on the distribution characteristics of the safety factor in the stable zone, a classification framework is proposed, dividing traffic tunnels into small (40-80 m²), medium (80-110 m²), and large (≥110 m²) cross-sections, with recommended safety factors of 1.24, 1.20, and 1.16, respectively; (3) By refining the safety factor, the threshold values of absolute gas emission rates for micro-gas, low-gas, and high-gas zones in the three tunnel categories are redefined, thereby establishing an optimized gas classification standard for traffic tunnels. This research provides valuable insights for the design and construction of gas-prone tunnels.

Key words: gas tunnel, gas classification standard, tunnel ventilation, wind speed heterogeneity；numerical simulation, safety factor