To exploit the influence of the tunnel face and the distance between the diameter and the orifice of a blast pipe on the ventilation effect in symmetric tunnel construction, this paper uses Fluent to establish a three-dimensional model and numerical simulation. Firstly, the accuracy of the numerical simulation is tested and then the distance between the orifice and tunnel face and the influence of the air duct diameter on the ventilation effect are studied, respectively. The results show that the ventilation effect is best when the wind pipe is arranged on one side of the tunnel wall (an asymmetrical layout), although the space in the tunnel is axisymmetric, and that the error of the numerical simulation is less than 5% of the measured value. When the distance between the orifice and tunnel face is 5 m, the uniformity of the air flow field near the tunnel face is poor; when the distance is 10 m and 12 m, an obvious vertex area appears in the tunnel. Furthermore, the uniformity of the wind velocity flow field is optimal when the distance is 8 m. When the air duct diameter is less than 1.4 m, there is a uniformity of the flow field near the tunnel face of the upper and lower benches; when the air duct diameter is more than 1.4 m, the tunnel face of the upper bench near the ground shows more obvious backflow. Therefore, it was determined that taking the air duct diameter as 1.4 m and the distance between the orifice and tunnel face as 8 m was the best combination for the design of ventilation in this project. It was also found that a better ventilation effect can be achieved when the distance between the nozzle of the ventilator and the tunnel face is 6 m–9 m and the wind speed of the nozzle is 6 m/s–8 m/s. In practical engineering, the wind speed and the required air volume should be taken into consideration to determine the diameter of the ventilator.

In order to study the application of grouting behind the lining wall in the treatment of leakage of subway tunnel during the operation period, the diffusion effect of grouting behind the wall in dense fill and loose fill was studied by the method of numerical simulation and model test, and the distribution of grouting vein in the process of grouting was analyzed. The results show that the results of numerical simulation and model test are basically the same, mainly as follows: In the dense soil, although the slurry will also expand along the tunnel lining wall, it is mainly jacking in the direction perpendicular to the lining structure, and it is unable to form a large area of enclosed solid behind the lining structure; In the loose soil, with the increase of grouting pressure, the slurry gradually approaches the wall After approaching the wall, it will expand along the wall, and, at the end of grouting, the slurry will be evenly distributed along the back of the tunnel lining structure and form an obvious closed reinforcement. It is concluded that: for the tunnel structure in loose soil, when the measures of grouting behind the wall are adopted to treat the leakage water, the spacing of grouting holes can be appropriately enlarged; for the tunnel in dense soil, the spacing between grouting holes should not be too large. More importantly, the correct grouting scheme design must be considered from the whole reinforced soil, rather than from the effect of a certain point. According to the specific situation and the expansion process of the slurry, the expansion direction of the slurry vein should be considered scientifically, so as to achieve good treatment effect of leakage water.