The selection of ventilation ducting for tunnel fans must fully consider factors such as in-tunnel airflow volume and velocity, duct durability, and cost. Typically, plastic ducting is used, with a diameter of 110 cm and a standard section length of 20 meters; modern rigid connectors are employed for joining sections. The ducting is installed along the tunnel crown, either at the center or slightly offset from the centerline. Anchor holes are drilled at 5-meter intervals, and the installation must meet specific tolerances: the sag (deflection) between suspension points must not exceed 150 mm per 100 meters, and axial deviation must not exceed 300 mm per 100 meters. Given the prolonged time required for air purification in the central section of the tunnel-and the difficulty of achieving air quality standards at the working face-a mixed ventilation approach is adopted, utilizing a forced-air (push-type) system with the fan installed at the tunnel entrance.
