# A Study on the Heat Transfer of Surrounding Rock-Supporting Structures in High-Geothermal Tunnels
## 1 Introduction  
With the rapid development of traffic engineering under complex geological conditions, there is a rapid growth in the number of tunnels constructed worldwide under high geothermal activity conditions recently, such as Gotthard-Basis Tunnel in Switzerland Swit, Apennine Railway Tunnel in Italy, Sangzhuling Railway Tunnel in China and so on [1,2]. High geothermal is an unavoidable and widely distributed problem in deep, long tunnel constructions. It may cause an increase of thermal stress and the degradation of the material properties of concrete [3], resulting in the failure of the lining structure in the tunnel [4, 5, 6]. Moreover, a high geothermal environment [7] also puts tunnel workers under terrible working conditions [8, 9, 10]. Therefore, the temperature fields of the surrounding rock and lining concrete become an urgent important issue to study to solve the high temperature-resistant problems in high geothermal tunnels. Previous research on the temperature field in tunnel engineering mostly focused on the cold-region tunnel. [PERSON] et al. [11] concluded that the flow of groundwater had a significant impact on the distribution of temperature of the surrounding rock by an experimental model test. [PERSON] et al. [12] tested the air temperature, wind force conditions and atmospheric pressure on the spot and proposed a newprediction model of freezing-thawing conditions concerning the combined convection-conduction in the rock surrounding tunnels in cold regions. [PERSON] et al. [13] did research on the three-dimensional temperature properties in cold-region tunnels by the finite element method. [PERSON] et al. [14] proved that the freezing-thawing behaviors of the rock surrounding a tunnel can be correctly predicted even if the air temperature along the tunnel is unknown. According to the heat transfer theory, [PERSON] et al. researched temperature, seepage and stress fields in cold-region tunnels and they also made nonlinear analyses of temperature distribution using finite element formulas. [PERSON] et al. [15] studied that it has an adverse effect on the freezing damage in the tunnel when the mechanical ventilation velocity was higher than natural velocity. The negative ventilation direction is helpful to alleviate freezing damage. [PERSON] et al. [16] predicted the temperature field of a railway tunnel. The study results demonstrated that the mechanical ventilation winds and train-induced winds should be considered in the engineering design of tunnels in cold regions, which has a significant impact on the distribution of the temperature field in the surrounding rock. In the aspect of high-temperature tunnels, the study results are mainly based on the influence of fire and smoke on the tunnel temperature field. The previous studies indicated that the initial fuel temperature significantly influences the flame spread behaviors over the liquid fuels and the temperature field in tunnels. [PERSON] et al. [17] investigated the typical smoke characteristic parameters, such as temperature distribution, and researched the impact of different fire positions on natural ventilation effectiveness in a tunnel by large eddy simulation [18]. The smoke layer interface height was also determined by conducting a 1/6 th scale tunnel model test in medium-scale tunnel fire scenarios [19]. [PERSON] et al. [20] showed that the smoke concentration significantly influenced the ceiling temperature. Based on the theoretical analysis and the curve fits of the tunnel ceiling temperature decay with distance from the fire source, a model for the ceiling temperature decline along the tunnel was proposed. [PERSON] et al. [21] investigated the distribution of temperature in tunnel fires by experimental tests and theoretical analyses. The factors that influence the smoke temperature distribution are discussed according to the equation they established. In summary, previous researchers have a provided number of valuable results on the temperature field in tunnel constructions.