## 5 Conclusions  
In the LTCC face, the roof, the top coal, and the hydraulic support interact with each other and are always in a dynamic coupling state. In order to study the movement law of the roof and reveal the bearing characteristics of hydraulic support in different surrounding rock fields, the different forms of movement instability of the upper immediate roof are explored, and the dynamic coupling model of roof-top coal-hydraulic support is established. The influence of different instability forms of the upper immediate roof on the crushing condition of the top coal is analyzed, and the bearing characteristics of the canopy under different instability forms are discussed. The following conclusions are obtained:  
1. Combined with the coupling mechanical model of roof-top coal-hydraulic support, the instability effect of the roof is quantitatively analyzed. It is concluded that the main factors affecting the working resistance of hydraulic support are the fracture position of the upper immediate roof, the acting force of the lower immediate roof, the additional force position of overlying strata, and the distribution of gangue in goaf. Figure 12: Load curve of the hinged joint between the canopy and the caving shield. 2. The rotary instability of the upper immediate roof leads to the obvious crushing of the top coal, which affects the contact area between the top coal and the canopy. Repeated contact collisions cause serious impact load on the hydraulic support. In particular, the rotary instability of the upper immediate roof at the coal wall causes cracks in front of the coal wall and a large amount of broken coal concentrated at the front end of the canopy. This causes the stress concentration in the coal seam to move forward, which in turn reduces the stability of the coal wall. In the LTCC face, improving the support area of the canopy and effective rib spalling prevention measures are conducive to improving the stability and reliability of the hydraulic support. 3. The instability of the upper immediate roof affects the state of the top coal, which leads to the uneven bearing of the hydraulic support, and makes the canopy show a downward trend. Although the existence of the column ensures the support performance of the canopy, it is easy for the stress concentration to occur at the column sockets, especially in the front column sockets. Therefore, the box structure and stiffeners can be set between the column socket and the canopy to ensure a more uniform stress distribution at the column socket. In addition, the back-end ribs and side ribs of the canopy will be continuously impacted by the broken and collapsed coal blocks. In the structural optimization, the back-end ribs and side ribs of the canopy can be strengthened. 4. In the case of rotary instability, the force of the hinged pin shafts is severe, but the peak and stable value of the hinged joint load are quite different due to the different positions of the rotary instability. Under the rotary instability at the coal wall, the stable value of the load is the largest, at 6950 kN. On the contrary, under the rotary instability at the roof cutting, the peak value of the load is the largest, at 13,560 kN. Therefore, the increase in the strength and toughness of the hinged pin shafts are favorable to improve the adaptability of the hydraulic support. The results provide the research suggestion for the coupling relationship between surrounding rock and hydraulic support and provide references for the bearing characteristics analysis and structural optimization of the hydraulic support. However, there are some limitations to this study. The influence of the coal caving process and the working face advancing process is not considered in this study, so the coupling model of the roof-top coal-hydraulic support including the tail beam can be considered in further research. In addition, early warning of roof instability is an effective means to reduce accident losses in time.