A new ventilation system for extra-long railway tunnel construction by using the air cabin relay: A case study on optimization of air cabin parameters length

Abstract In the construction of an extra-long tunnel through a long, inclined shaft, problems are often encountered. For example, the long ventilation distance and insufficient air volume in the working face make it difficult to discharge pollution out of the tunnel at a specified time. This paper proposes a new ventilation system involving an air cabin relay that can be used during the construction of extra-long railway tunnels. A 3D numerical model validated with field test data was employed to discuss the influence of the air cabin length, the partition length, and the arrangement of the fan on the ventilation efficiency of the axial fan. In addition, we performed careful analysis of the specific status of in situ CO migration in the originally forced ventilation and air cabin ventilation. The results show that, when the length of the air cabin is increased from 10 to 40 m, the relative pressure on the end face of the fan increases. When the length of the air cabin exceeds 40 m, the growth of the relative pressure at the end face of the fan shows a sharply decreasing trend. This partition will affect the airflow in the air cabin and generate greater swirling flow, reducing the ventilation efficiency of the fan. The best arrangement of axial flow fans is symmetrical along the axis, for which the largest velocity and drainage range of airflow in the air cabin are obtained. Because the forced ventilation is limited by the section size of the inclined shaft and the site layout method, the operating conditions in the extra-long railway tunnel cannot be met. To address this, our design includes a sealed air cabin, which was set up at the intersection of the main hole and the inclined shaft to form relay ventilation; this can greatly extend the ventilation distance, enhancing the ventilation efficiency and improving the tunnel air quality, and establishes a new method for the ventilation of extra-long tunnels during the construction stage.