## 1 Introduction
[PERSON] et al. [22] investigated the tunnel temperature distribution both with and without an insulating layer, and their research came to the conclusion that an insulation layer improves the effect of heat insulation in high-temperature tunnels noticeably, but the insulating effect drops sharply with the increase in the rock temperature. [PERSON] et al. [23] studied the impact of non-water-reactive polymers for high-geothermal tunnel insulation. The findings demonstrated that the temperature of the surrounding rock increased with thermal conductivity and polymer thickness. [PERSON] et al. [24] applied field experiments and numerical simulations to determine the response characteristics of a thermal environment for a wall rock that has an air layer structure. Even though using an insulation layer has a significant cooling effect on the tunnel, it is obviously not economical to follow the tunnel excavation and lay the whole tunnel. Furthermore, many tunnels extend several hundred meters or even thousands of meters in actual projects. It was found in previous studies that the heat exchange between the palisades and airflow in a tunnel operation area is small due to the low airflow velocity [25]. On the contrary, the heat exchange is strong and rapid in the excavation area owing to more intense airflow and temperature changes in the surrounding rock [26]. As a result, using a technical method that combines ventilation and thermal insulation is a possible solution for coupled cooling and to deal with the prominent heat hazards in an excavation area. And the establishment of partial insulation can effectively lower the cost of the initial construction. Based on the actual condition of the project, a conceptual model of a coupled cooling system for auxiliary ventilation and partial thermal insulation (PTI) is proposed. As shown in Figure 1a, a movable TIL is set within 6 m of the WF to avoid direct heat transfer between the airflow and high-temperature rock as well as to better realize the PTI effect. There are pulleys arranged at the bottom of the PTI unit. When workers are working, the movable TIL is near the WF at the same time as them. As the operations, such as drilling and loading explosives, are concluded, the PTI unit returns to the safe area together with the workers and waits for the stage after blasting. A heat exchange layer is set up outside the thermal insulation, and cold water is delivered to the inside of the insulation through the constant temperature water unit to further reduce the temperature. On the one hand, the PTI can avoid the wastage generated by the overall installation of insulation and reuse movable TIL, and on the other, it can enhance ventilation and cooling effects, preserve the airflow cooling capacity, and promote the decline in the cooling limit. Figure 1: A schematic diagram of a coupled cooling system for auxiliary ventilation and PTI. **(a)** The partial thermal insulation (PTI) scheme. **(b)** A conceptual model of a coupled cooling system for ventilation and PTI. In this study, the principle of coupled cooling is analyzed. To comprehensively explore the thermal performance of a coupled cooling system in a tunnel, a scale model test platform was constructed. With local insulation layers used in the working area of a high-temperature mine tunnel, the variation law of ambient temperature under pivotal factors was investigated, including the ventilation volume, the length and thickness of the insulation layer, ventilation duct height, and the distance between the VDO and WF. And then the orthogonal test was used to investigate the experiment and assess the impacts of different factors on the tunnel's thermal environment. This research provides a theoretical foundation and technical guidance to improve the cooling effect of deep mine tunnels in an effective and economical manner as well as enhance the thermal comfort levels of workers.