A new air cabin ventilation relay system and its optimization design for extra-long tunnel construction, with multiple working faces

In extra-long tunnels, with multiple working faces under simultaneous construction, press-in ventilation requires branching ducts, causing significant air pressure loss, while partition ventilation is costly and inefficient when applied to long cross adit. This study proposes an optimized air cabin relay ventilation system. Using a field-validated numerical model, the effects of unilateral length, fan opening condition, inlet air velocity, and inlet angle are analyzed and optimized. Results show that ventilation efficiency increases by 13.3% as unilateral length grows, peaks at 15 m, then declines before stabilizing. Ventilation efficiency is relatively higher when the outlet fans on the right side of branches are activated. The pressure extremes within the air cabin are linearly correlated with inlet air velocity. Ventilation efficiency is maximized when inlet air volume matches outlet demand. Efficiency is higher when the air cabin inlet is diagonally aligned with the main tunnel and lowest when it is perpendicular to the main tunnel. Grey correlation analysis identifies inlet air velocity as the most significant factor on fan efficiency, followed by unilateral length and inlet angle. This system and its optimization design provide a valuable solution for ventilation challenges in extra-long tunnel construction, with multiple working faces.