Thermal environment analysis for the deep-buried TBM construction tunnel considering the influences of surrounding rock heat transfer and ventilation system

The thermal environment in deep-buried underground engineering is a vital issue related to construction safety. Surrounding rock heat transfer and ventilation are key factors affecting the thermal environment of deep-buried tunnels. Filling media in fractures are important for determining the surrounding rock thermodynamic properties. However, the effect of filling media on surrounding rock heat transfer is ignored in existing thermal environment studies. Moreover, the Reynolds-averaged Navier-Stokes model adopted in existing ventilation simulation studies can hardly be used to capture the turbulent transient pulsation, leading to imprecise determination of the temperature distribution in tunnels. To obtain accurate thermal environment information for deep-buried tunnel construction, the surrounding rock equivalent thermal conductivity considering the influence of fracture filling media was first calculated based on fractal theory and discrete fracture network modeling in this study. Then, the heat transfer model of the surrounding rock and the hybrid large eddy simulation/Reynolds-averaged Navier-Stokes model of ventilation were coupled to develop a numerical method for thermal environment analysis. The numerical method was verified by an in-situ test, and the method was used to analyze the thermal environment of a deep-buried tunnel boring machine construction tunnel. The obtained results showed that the surrounding rock equivalent thermal conductivity is 1.3 W/(m·K), the heat dissipation power of the surrounding rock accounts for 60.94 % of the total heat dissipation power and the presence of filling media in fractures leads to an 11.24 % decrease in the ratio of the heat dissipation power of the surrounding rock to the total heat dissipation power. The ventilation system greatly influences the air temperature inside the tunnel and the temperature distribution in the near-wall surrounding rock. This study provides useful guidance for construction environment management in deep-buried tunnels.