Abstract: Hypobaric hypoxia at the working face of high-altitude tunnels poses a significant risk to worker safety. To address this, the authors propose a novel pressurized ventilation system tailored for high-altitude construction tunnels, utilizing a resistance-increasing regulation method commonly used in mining. This system is designed to elevate the pressure in the working area, creating a comfortable oxygen-rich environment that meets safety requirements. Similarity principle numbers and ratios are derived and a test bench is constructed for similar construction tunnels based on Reynolds (Re) and Euler (Eu) number similarity principles. The feasibility of pressurized ventilation systems is validated through a similar experiment. How an altitude ranging from 3 000 to 3 600 m affects the flow area ratio of the windshield is investigated, and the data are  fit nonlinearly to obtain an empirical equation. The effects of airflow variations on the pressurized ventilation system is examined. The findings are as follows: (1) The pressurized ventilation system allows the partial pressure of oxygen in the tunnel working area at an altitude of 3 500 m to be equivalent to that at 2 500 m when the flow area ratio of the windshield and the fan frequency are 15.3% and 46.3 Hz, respectively. (2) The flow area ratios of the windshield for tunnels at altitudes of 3 000 and 3 600 m are 17.2% and 15.1%, respectively. As altitude increases, the flow area ratio of the windshield decreases; however, this ratio stabilizes within a certain altitude range. (3) At higher altitudes, increased air volume leads to greater pressurization in the working area, with the rate of change in pressurization varying significantly with airflow volume at the same altitude.

Key words: high-altitude tunnel, pressurized ventilation, similar experiment, flow area ratio