# Experimental Study on Freezing Front Model of Alpine Tunnel under Wind Field
## 1 Introduction  
With the increasing demand for transportation infrastructure construction in the Qinghai-Tibet Plateau and Northwest China, the construction scale of tunnels in high altitude cold regions is also expanding year by year, and the phenomenon of frost damage in railway and highway tunnels in cold regions is very common and serious [1, 2]. Therefore, reducing tunnel frost damage has become a key scientific problem that needs to be solved urgently at present, and it is also a difficult and key point for scholars in the field of alpine tunnel engineering to study [3, 4]. Especially in the extreme environment outside the tunnel, cold air enters the tunnel and repeatedly exchanges heat with the lining, resulting in severe frost damage to the tunnel lining, invert and drainage structure. These problems have been an issue for the operation management and safe driving of the alpine tunnel project [5, 6]. Both domestic and foreign scholars have made a lot of achievements in the study of tunnels in cold areas under the action of wind flow field, most of which are basedon model tests and numerical simulation, etc. [7; 8]. According to the research results, when the external air flows into the tunnel, the heat exchange between the air flow and surrounding rocks is the most intensive at the tunnel entrance; it then gradually decreases with the increase of ventilation distance, showing an inverted \"V\" variation trend on the whole. [PERSON] and [PERSON] (1996) obtained the analytical solution of the gas temperature field in the underground wind tunnel according to the law of conservation of energy [9]. [PERSON] et al. (1996, 1999) predicted the freeze-thaw conditions of 46 surrounding rock tunnels in cold areas based on the combined convection-conduction model of 47 on-site temperature, atmospheric pressure and wind conditions [10; 11]. [PERSON] et al. (2002) deduced the analytical solution of the temperature field of circular tunnels and proposed the calculation method of the thermal insulation layer of tunnels in cold areas [12]. [PERSON] and [PERSON] (2007) analyzed the effect of temperature control on permafrost tunnels and established stable conditions related to melting depth and suitability for use in construction [13]. On the basis of thermal conductivity seepage theory, [PERSON] et al. (2007) studied the influence of thermal insulation layers on controlling water leakage in permafrost tunnels by considering the coupling effect of seepage and temperature field, and carried out the three dimensional nonlinear analysis of the Kunlun mountain tunnel with and without an insulation layer [14]. Taking Zila mountain tunnel as an example, [PERSON] et al. (2021) studied the dynamic change of the temperature field during the operation of the tunnel by adopting the convection-conduction coupling transient heat transfer model [15]. In recent years, the finite element analysis method is often used to solve the heat transfer problem between tunnel surrounding rock and air [16]. Based on the heat transfer theory, [PERSON] et al. (1999) used the finite element formula to make a nonlinear analysis of the temperature field, seepage field and stress field related problems in cold zone tunnels [17]. In order to study the influence of wind flow field on the temperature of tunnel-surrounding rock in cold areas, [PERSON] et al. (2014) established the temperature field model of tunnel-surrounding rock, which includes the governing equation of surrounding-rock temperature, the governing equation of air temperature field in tunnel and the governing equation of wind flow in turbulent field [7]. On this basis, a numerical analysis method was adopted. The variation rule of surrounding-rock temperature field and specific insulation measures under ventilation conditions of Jialongla Tunnel in Xizang Province are discussed. Both mechanical ventilation and train-induced wind during train operation in the cold zone tunnel have a great influence on the temperature field inside the tunnel. [PERSON] et al.