Evolutionary law of temperature field in thermal water-bearing tunnels and analysis of thermal insulation effect of grouting water-sealing

To investigate the thermal evolution of surrounding rock in high-water-temperature tunnels where both heat conduction and convective heat transfer between geothermal water and rock coexist, this study derives a finite difference solution for the coupled thermal-hydraulic temperature field and develops a three-dimensional numerical model that integrates the high-temperature water-saturated rock mass with tunnel air. A parametric study is conducted to analyze the effectiveness of grouting for water sealing and thermal insulation. Additionally, a physical model test system for high-temperature tunnels is developed to validate the finite difference solution and numerical results. The findings indicate that: (1) when rock permeability exceeds 5×10⁻⁷ m/s, convective heat transfer from thermal water maintains the rock at its initial high temperature; as permeability decreases, rock temperature declines, but further reduction below 1×10⁻⁹ m/s yields diminishing cooling returns. (2) Grouting significantly reduces convective heat transfer between water and rock, thereby lowering the temperatures of both rock and air. For rock with a permeability of 1×10⁻⁶ m/s, a grout zone with permeability two orders of magnitude lower and a thickness of 3 m achieves more pronounced cooling. (3) Model tests demonstrate that initial ventilation leads to rapid rock cooling, which stabilizes over time; wall temperature trends align with the finite difference solution, and the relative errors in wall and outlet air temperatures between simulation and experiment are within 15% and 5%, respectively. Combined grouting and enhanced ventilation are recommended for thermal control in high-temperature tunnels. The results provide theoretical guidance for the cooling design of similar geothermal tunnels.