The air density in high altitude gas tunnel is small and the air supply is difficult. The jet tunnel ventilation is a common construction ventilation mode. In order to explore the pollutant distribution characteristics and the optimal ventilation length of tunnel ventilation in high altitude gas tunnel, Ningchan tunnel has been taken as the engineering background, the fluid dynamics software Fluent has been used to establish a three-dimensional model of jet tunnel ventilation, the distribution characteristics of methane, hydrogen sulfide and other harmful gas in the tunnel have been studied, and the optimal ventilation length of tunnel ventilation in high altitude gas tunnel degree has been explored. The results show that: the minimum ventilation length required in the existing technical specifications of gas tunnel is not reasonable, which leads to the existence of low-speed wind area in the tunnel, and harmful gas is easy to gather in the single head section, and the gas concentration can reach 0.59% at 2 m away from the working face; by reducing the ventilation length, the gas concentration in the single head section can be effectively reduced, and when the ventilation length is 1,200 m, the gas concentration at 2 m away from the working face will be reduced to 0.31%; setting local fan in front of the roadway can also significantly improve the accumulation degree of harmful gas in the single end section. The maximum gas concentration of working face reduced to 0.24%, and the average gas concentration of reduced to 0.15%. The results can provide reference for ventilation scheme of high altitude gas tunnel construction.

Effective real-time treatment and control of harmful gases are key to ensuring the safety of tunnel construction workers. Currently, the monitoring ability of harmful gases is insufficient to match the processing needs, which poses significant risks to the safety of tunnel construction workers. This paper proposes an advanced perception and treatment method for harmful gases during tunnel construction, utilizing the DeepAR algorithm. Real-time monitoring of the concentration and diffusion of harmful gases is conducted, and a harmful gas concentration prediction model is established using the DeepAR algorithm, achieving advanced perception of harmful gases during tunnel construction. The harmful gas treatment plan is developed in advance, and the effectiveness of the proposed method is demonstrated by simulation testing under realistic field scenarios and comparing with other prediction models. The method was applied in a coal mine tunnel in Qinghai Province, achieving an accuracy rate of 94.3%, which is higher compared to those obtained using RNN and LSTM algorithms. Moreover, the computational time is less than 60 s. The method provides timely perception of the concentration distribution of harmful gases in the tunnel and proposes targeted treatment measures, verifying the effectiveness of the prediction model from the perspective of practical engineering application.

Aiming at the problem that the uneven deformation of the tunnel surrounding rock in the deep inclined rock strata caused local instability, an innovative balanced-yielding support technology was proposed with the engineering background of the Shangping tunnel in Huafeng Mine. Based on the mechanism analysis of this technology, the specific implementing steps were proposed. It mainly included in situ stress analysis, the stress distribution of the tunnel surrounding rock with different sections, the design of the parameter of bolt-cable and yielding structure, and supporting effect evaluation. The results showed that (1) the stress concentration appeared at the top corners of the lower side and the bottom corner of the upper side of the rectangular and semicircular arched tunnel. (2) Compared with rectangle and vertical-wall semicircular arch tunnels, the trapezoidal tunnel could relieve the shearing effect of the inclined rock strata. (3) The length, prestress, spacing-row distance of the bolt, and the parameter of the yielding structure were all optimally designed to form the balanced-yielding support system. (4) In engineering application, the maximum deformations of the roof, right side and left side, were less than 80 mm. Compared with the original support system, the shallow separation of the trapezoidal tunnel supported by the balanced-yielding support system had been reduced by 147%.

It is the key and difficult point to ensure the safety of tunnel construction by ventilation in high gas tunnel construction in high altitude and cold area. Taking ning-chan high gas tunnel as the research object, the ventilation of the tunnel is calculated, the ventilation parameters are optimized, the ventilation equipment is selected according to the calculation results, the location of the ventilation equipment is optimized, and the reasonable construction ventilation scheme is determined. The results show that through the design of the above ventilation scheme and the control of the site, it can not only ensure the ventilation demand of the super long and high gas tunnel construction in the high cold and high altitude area, but also ensure the tunnel construction in winter, and effectively save the construction ventilation cost.

Due to the special mechanical properties of macker rock, problems may be caused easily if the pressure of the surrounding rock calculated from the standard empirical equation is used in the structural design of tunnel support, such as obviously insufficient bearing capacity of the support structure, large deformation, and collapse. Taking the Jiangluling Macker Tunnel in Gonghe-Yushu Highway as an example, the distribution pattern of plastic zone of the surrounding rock and the calculation method and reasonable values of pressure of the surrounding rock are studied in this paper, by means of theoretical analysis, numerical computation, and field measurement data. The results show that the elastic-plastic analysis method is suitable for the pressure of the surrounding rock of macker tunnel. The influence radius of the plastic zone of the surrounding rock can be 32 m, and the lateral pressure of the surrounding rock of the tunnel is equivalent to the vertical pressure. In the absence of test conditions and measured data, the pressure of the surrounding rock can be approximately 0.83 MPa for the purpose of design of tunnel support structure. This conclusion provides technical support for projects in similar conditions.