## 6 Results and Discussion  
Combined with the geological and mining conditions of the experimental area, the UCG test station mining is 4 strips, the gasifier mining depth is 259 m, the combustion cavity width is 16 m, and the isolation coal pillar width is 32 m. The gasification time of each strip was 3 months, and the combustion surface temperature was 1400\({}^{\circ}\) after the gasification of the gasifier was stabilized. The temperature field distribution of the roof, floor, and coal walls on both sides after gasification can be calculated as shown in Figure 8.  
The mechanical parameters distribution of the surrounding rock around the combustion cavity was calculated according to the temperature field expansion characteristics. The basic roof subsidence was obtained using the calculation method of the basic roof subsidence space of UCG, as shown in Figure 9.  
As the roof subsidence space is small, the rock layers can be considered to have no delamination between them. At this time, the subsidence space of the roof subsidence upward transfer process follows the principle of equal volume. At this time, the subsidence coefficient can be considered to be 1. By comparing the geological conditions of the mining area near Ulanqab, the main influence angle tangent is 1.8. The expected method of UCG surface subsidence is used to calculate its surface subsidence curve as shown in Figure 10. According to the figure, the expected maximum surface subsidence is 41 mm and the measured maximum surface subsidence in the experimental area is 36 mm, which  
Figure 8: Temperature field distribution in the combustion cavity. **(a)** Roof temperature field distribution. **(b)** Floor temperature field distribution. **(c)** Coal wall temperature field distribution. Figure 9: Spatial distribution of roof subsidence of UCG. is expected to be 11% different from the measured results. This method can be used to predict the surface subsidence of UCG. Through numerical simulation, we found that the thermal stress and coal-rock burnt by high temperature affect the strata movement characteristics of UCG, of which the coal-rock burnt is the main control factor. Although the high-temperature thermal stress has a certain contribution to this process, its impact is relatively small. There have been studies reporting the impact of high temperature on the movement and deformation of strata during UCG, but most of the literature only studies the impact of high-temperature thermal stress or comprehensively considers high-temperature thermal stress and coal-rock burnt, resulting in insufficient research or increasing the complexity of subsequent research [22; 44; 45]. Undoubtedly, our research is consistent with previous results. Whether it is high-temperature thermal stress or coal-rock burnt, it will increase the degree of movement and deformation of the overlying strata. Our research results can grasp the main influencing factor of coal-rock burnt, omitting the subtle elements and simplifying the subsequent research process based on not affecting the research results. Currently, the prediction of surface subsidence caused by UCG is generally reference strip mining ignoring the influence of high temperature, resulting in limited prediction accuracy [26; 46; 47]. In this study, considering the coal-rock burnt, the prediction model of surface subsidence of UCG is established by innovatively combining the elastic foundation beam theory and random medium theory. We applied this method to the UCG test station in Ulanqab and estimated a maximum surface subsidence of 41 mm (Figure 11). At the same time, we established a continuous observation station for surface subsidence on the surface and observed a maximum surface subsidence of 36 mm with a difference of only 5 mm. This proves that the method proposed in this paper has high prediction accuracy. The author believes that improving UCG efficiency while reducing its environmental risks is currently a research focus in the field.