Comparison Thermal Insulation Effects of Different Thermal Insulation Materials for a Roadway Tunnel at Southeast Edge of the Qinghai-Tibet Plateau

In seasonal frost regions, tunnels are affected by frost damage after excavation. At entrance and exit section of tunnels, thermal insulation layer (TIL) is widely used to mitigate this problem. In this study, a moisture-temperature coupled mathematical model was established. Based on field observed air temperature at entrance section of Altun mountain tunnel, the thermal regime of surrounding rocks was investigated. Moreover, a comprehensive evaluation method was established to evaluate the thermal insulation effects of seven thermal insulation materials. The results showed that, with increase in thickness of TIL, maximum frozen depths of surrounding rocks decreased almost linearly. At the vault (H1), arch hance (H2), foot (H3), and inverted arch (H4) of the tunnel, the thermal insulation effect was different. When the thickness of TIL reached to 5 cm, there would be no seasonal freezing process at the four points. Seven types of TIL were considered for the thermal insulation of the tunnel. The optimal thickness of them was 4.2, 11.0, 5.5, 6.3, 10.2, 12.8 and 8.5 cm. To ensure the surrounding rocks do not experience freezing process, rigid polyurethane foam would be the best choice. Considering the cost, dry process aluminum silicate fiber would be a better one.