In response to the unsatisfactory treatment effect and high construction risk of shallow buried tunnels crossing high gas formations, based on the theory of fluid porous media, the coal seam gas displacement and extraction technology is applied to the construction treatment of shallow buried tunnels in high gas formations. The performance of gas displacement in the formation was analyzed using theoretical analysis and numerical simulation methods. The influence range and time of gas displacement were determined. Four factors that may affect displacement performance, including negative pressure of drainage, gas injection pressure, formation permeability, and borehole diameter, were studied. Finally, the numerical simulation results of gas displacement in the formation were demonstrated through on-site experiments. The results show that under the condition of negative pressure P_C = 50 kPa and injection pressure P_Z = 2.0 MPa, when the distance between injection and extraction holes is 12 m, gas injection for 40 min is used, and the displacement effect achieved by pumping for 90 min is better. The smaller the suction negative pressure, the better the displacement performance, but the impact of suction negative pressure on the displacement process is relatively small; The increase of gas injection pressure can significantly increase gas drainage capacity and reduce displacement time; There is a nearly linear positive correlation between the decrease in formation gas, gas flow rate from drainage holes, and permeability; For the commonly used borehole diameter, increasing the borehole diameter has little effect on the effectiveness of gas displacement control in the formation. Due to factors such as geological conditions, equipment limitations, and construction disturbances, there are certain differences between on-site experiments and numerical simulations of gas content monitoring data. However, the two have a high degree of consistency in terms of displacement effect and time progress.

Large-scale water inrush occurred in the horizontal lead of the No. 2 inclined shaft of the Hongdoushan tunnel, which mainly passes through non-soluble rock formations such as mica granite and metamorphic granite mylonite. In order to predict the water inrush volume of the tunnel in the granite alteration zone, the engineering characteristics of the granite alteration zone in the Hongdoushan tunnel and the cause mechanism of the water inrush are analyzed. A relevant hierarchical structure model of water inrush evaluation was established. Combining the hydrogeological conditions, geological conditions of the study area with the on-site monitoring, the hazard of the Hongdoushan tunnel’s water inrush is classified. Finally, fuzzy mathematics is used to predict the water inrush from the horizontal guide of the No. 2 inclined shaft of Hongdoushan tunnel. The results show that: (1) The influencing factors of water gushing in Hongdoushan tunnel are mainly divided into three aspects: engineering geology, hydrogeology and tunnel working conditions, with 9 factors in total. Based on these factors, the predicting model is thus established. (2) The predictions of water inflow given by the proposed model have a percentage error of 2.61 compared to the actual one, which could meet the requirement of engineering application. Thus, the proposed model could provide accurate predictions on relevant engineering.

The geological conditions of the western Sichuan Plateau are complex, and the problem of harmful gases in the process of tunnel construction has become increasingly prominent, which has brought unprecedented geological challenges to the western development strategy. In view of the complex distribution of harmful gases in western Sichuan, based on the collection and analysis of regional geological data and tunnel data in the western Sichuan plateau, the study is conducted using geological history analysis, oil and gas accumulation theory, field detection and other methods main components of harmful gases in the complex structural area of western Sichuan. The results show that: The are gas (methane), hydrogen sulfide and carbon dioxide. There are two kinds of harmful causes: inorganic causes and organic causes. Gas mainly comes from organic causes, hydrogen sulfide mainly comes from inorganic causes, and carbon dioxide is mixed causes. Harmful gases are mainly distributed in the core area of folds, deep strata, near compression-torsion faults, carbonaceous strata or igneous rocks or metamorphic rocks, and the distribution rules are interrelated. The research results have a guiding affect on the prediction and control of harmful gases in the tunnels of western Sichuan Plateau.