Numerical Study on the Temperature Field of a High Geothermal Tunnel with PCM-Modified Support Structure

High geothermal environment brings challenges to the construction and maintenance of the support structure of tunnels. This motivates the proposal of an innovative PCM (phase change material) modified support structure, which exhibits advantages in heat reduction. A numerical model was established to investigate the temperature field of the high-geothermal tunnel, where temperature evolution of the ambient and support structure were obtained. Influence of the mass fraction, the phase change temperature window, and the latent heat of the PCM was evaluated. It is found out that, right after the excavation, temperature of both the air and the supporting structure increases till a maxima, which is followed by progressively decrease to a steady state. The larger the mass fraction of PCM, the better heat reduction is achieved. It is characterized by a decreased maximum temperature and an increased time duration in reaching this maxima. Furthermore, the smaller phase change temperature window and the larger latent heat can prevent more thermal load from the surrounding rock entering the ambient, providing better construction environment.