During the operational ventilation process of high-altitude helical tunnels, the installation method of jet fans is a key factor in determining the ventilation efficiency of the tunnel. In this study, the CFD numerical simulation method is adopted to establish three-dimensional ventilation models of helical tunnels with different curvature radii. Through orthogonal experiments, the effects of tunnel curvature radius on the characteristics of the air jet flow field, under the coupled influences of factors such as lateral spacing of jet fans, vertical height of fans, longitudinal spacing, and lateral offset, are investigated. The results show that when R = 500 m, 600 m, 700 m, and 800 m, the longitudinal spacing has the most significant impact on ventilation efficiency, followed by vertical height, with lateral offset and fan spacing having the least impact. The optimal spacing and vertical height of the fan groups remain consistent under different curvature radii, at 1.25D (fan diameter) and 15 cm, respectively. The optimal longitudinal spacing of the fan groups is 90 m, 90 m, 135 m, and 90 m, respectively. Shifting the fan groups 0.25 to 0.75 m towards the inner side of the tunnel helix (for R < 700 m) can optimize the flow field distribution within the tunnel. Finally, expressions for the relationship between the helical radius and the lateral offset and longitudinal spacing of the fan groups are established for the optimal installation parameters of fan spatial positions under different helical tunnel radii.

In tunnel operation ventilation systems, the arrangement of jet fans plays a decisive role in ensuring ventilation efficiency. Curved tunnels, due to their unique radius of curvature, exhibit significant differences in fan installation parameters and jet flow field distribution compared to traditional straight-line tunnels. In order to investigate the distinct characteristics, this research utilized computational fluid dynamics (CFD) simulation methods to analyze the ventilation performance of both an innovative, adjustable jet fan system and conventional jet fans within the context of curved tunnel configurations. The findings reveal that by adjusting the horizontal deflection angle of the novel jet fan, the flow field distribution can be effectively optimized, and the jet effect can be enhanced, thereby improving ventilation efficiency. Compared to traditional jet fans, the novel fan demonstrates a significantly greater capability in flow field optimization, especially when its horizontal deflection angle is adjusted, showing a trend where the jet effect initially increases and then decreases, with the longitudinal impact range being adjustable within a range of 5 m to 25 m.

In high-altitude highway tunnels, the efficiency of jet fans significantly impacts the performance and energy consumption of ventilation systems. To optimize jet fan efficiency under such conditions, this study combines outdoor model experiments with numerical simulations of physical models in longitudinal jet ventilation systems. A model was established using SpaceClaim (ANSYS 2022 R1), and numerical simulations were conducted using Fluent software (ANSYS 2022 R1) to obtain results. The effect of different mounting inclination angles (0° to 10°) on the performance of a jet fan was experimentally investigated, and a correlation formula for the lift pressure of the jet fan under different inclination angles was established. Comparative results demonstrate that the numerical simulations accurately capture the variation trend of fan lift pressure under different tilt angles observed in the experiments. Specifically, the lift pressure of the jet fan initially increases and then decreases with increasing tilt angle. Comparative analysis of pressure rise at installation angles of 0°, 2°, 3°, 4°, 5°, 6°, 8°, and 10° revealed that a peak pressure rise of 19.66 Pa was observed at 4° installation, demonstrating optimal performance at this angle. The velocity distribution indicates that tilt angles between 0° and 4° increase the airflow influence range, beyond which efficiency decreases due to kinetic energy loss at the base. The study determined that under these conditions, a jet fan installed at a 4° inclination angle exhibits optimal performance in high-altitude straight tunnels and is thus identified as the optimal installation angle. At this angle, both pressure-rise efficiency and airflow stability are effectively balanced; this configuration provides a critical design basis for energy-saving optimization in high-altitude tunnel ventilation systems.

Excavations in urban cores, in close proximity to existing structures, can significantly influence the structural loading. This study, based on a specific section of the foundation pit for the Yaoziqiu area road network project, constructs a mechanical analysis model to assess the impact of foundation pit construction on adjacent buildings. The research examines how various factors, including the distance between the building and the pit, pile length, retaining wall thickness, and the depth of the retaining wall’s embedment, affect the deformation response of the structures. The results indicate that when the building is 5 m away from the foundation pit, the maximum pile foundation settlement is 13.45 mm. When the distance is 30 m, the settlement value is 6.91 mm, with a decrease of 6.54 mm. The effect of foundation pit excavation on pile foundation settlement is significantly reduced when the pile length exceeds 15 m. When the thickness of the retaining wall increases from 0.5 m to 0.7 m, the maximum settlement of the building foundation is reduced by 1.34 mm, a decrease of 8.38%. When the thickness increases from 0.9 m to 1.1 m, the maximum settlement of the building foundation is reduced by 0.6 mm, a decrease of 4.17%. When the embedded depth of the retaining structure increases from 10 m to 15 m, the maximum settlement is reduced by only 1.05 mm. When the embedded depth is increased to 25 m, the change in the settlement value of the building foundation is within 0.2 mm. This study offers a detailed quantitative analysis of the factors influencing structural deformation, providing specific guidance for developing risk minimization strategies in planning excavations near existing structures.