Abstract: Improving the accuracy of air-duct air leakage in long-distance tunnel dead-end forced ventilation is crucial for determining the optimal relay fan installation locations and ensuring ventilation efficiency. First, a theoretical model is established to deduce the air leakage rate and volume for each unit section along the ventilation pipe. A Python-based program is developed to analyze the leakage rate along the pipe. The proposed model is then compared with existing methodologies to evaluate its advancement. Second, a method is proposed to determine relay fan installation locations in long-distance forced ventilation systems under leakage conditions. Using the large-mileage side of the slope shaft work area of the Hefei-Wuhan high-speed railway tunnel as a case study, relay fan selection is performed based on actual engineering situations. The proposed method identifies the relay fan installation location for different pipe diameters to satisfy construction ventilation requirements. The designated location corresponds to the point of minimum wind pressure inside the ventilation pipe, as determined by the theoretical model. Finally, computational fluid dynamics simulations are employed to validate the accuracy of the theoretical model and the method′s effectiveness in determining relay fan installation locations. Results demonstrate that the wind speed at the air-duct outlet aligns most closely with the recommended value when a 1.5-m-diameter air duct is used on the long-distance side of the inclined shaft work area. The most effective ventilation effect is achieved when an SDF (A)-2-NO 4.0 relay fan is installed at 2 200 m for ventilation.

Key words: tunnel, relay fan, air leakage rate of air duct, air leakage volume, theoretical calculation model