Evolution Law of the Thermal Field of Surrounding Rock in High Rock Temperature Tunnels Under Varying Heat Sources

High rock temperature (HRT) and its associated thermal hazards, alongside secondary mechanical risks such as swelling pressures induced in clay layers, pose severe threats to the construction safety of deep-buried tunnels. This study aims to quantitatively reveal the evolution laws of the surrounding rock temperature field under varying heat source conditions. A combined approach of physical model testing and numerical analysis was adopted. Utilizing an independently developed test system with a 1:13 geometric similarity ratio, the coupled rock-heat-ventilation environment was simulated. A transient conduction-convection 3D numerical model was established in COMSOL and verified against experimental data under benchmark conditions. The research confirms that under the influence of localized block heat sources, the temperature field in the far-field region follows a significant linear attenuation law rather than the traditional exponential distribution, with a prototype-equivalent gradient of approximately 0.69 °C/m. Furthermore, the study quantitatively identifies 8 m3 as the critical volume for heat source geometric saturation, beyond which the incremental temperature rise efficiency decreases by 25%. It is further revealed that the effective cooling depth of conventional ventilation is only approximately 0.35 m, indicating a significant “ventilation shielding effect” within the deep surrounding rock.