Application of Underground Thermal Energy Storage in Cross-Seasonal Freeze Prevention of Tunnels in Cold Regions

Frost damage not only affects the normal functioning of tunnels but also jeopardizes their structural stability, possibly leading to tunnel abandonment.  Passive methods (e.g., insulation layers, thermal insulation doors, and anti-snow sheds) cannot completely eliminate frost damage due to cumulative freezing effects, while active methods (e.g., electric heat tracing, air curtain insulation, and ground source heat pump) suffer from high installation and maintenance costs and significant energy consumption. To effectively eliminate frost damage while reducing costs and energy consumption, a novel technology utilizing underground thermal energy storage technology for cross-seasonal frost protection in tunnels is proposed. This technology converts solar energy into heat energy via solar collectors before the cold season, then the heat energy is induced and stored into the surrounding rock around areas prone to frost damage by heat pipes. The stored heat energy automatically heats the tunnel during the cold season, driven by temperature differentials. To evaluate the feasibility of this technology in various cold regions, a coupled heat transfer model of solar-geothermal exchanger-heat pipe is developed, and a model test is conducted to validate the accuracy of this coupled model. The effects of groundwater seepage, heat storage locations, and tunnel ventilation on the frost protection performance of this technology are investigated through the validated model. Meanwhile, the influence mechanisms of these parameters on underground thermal energy storage and cross-seasonal frost protection in tunnels are determined by analyzing computational results. The optimal thermal storage locations and timing under different groundwater seepage and tunnel ventilation conditions are also identified. Specifically, this underground thermal energy storage technology can raise the average temperature of frozen areas in tunnels above 0 degrees Celsius. When groundwater seepage exists near the tunnel, the heat storage location should be situated upstream of the groundwater, and the distance between the heat storage location and the tunnel should gradually increase as the groundwater seepage velocity increases. The length of the energy storage area gradually increases as the wind speed at the tunnel entrance rises. The appropriate location for heat storage can significantly reduce heat storage time and enhance the antifreeze effectiveness of tunnels. This technology utilizes underground thermal energy storage to precisely eliminate tunnel frost damage while offering the advantages of low energy consumption and low cost, providing a green and sustainable frost prevention solution for tunnels in cold regions.