Abstract: The roof of the stope in the western region is thick and hard. The broken rock often forms large key blocks. The stability of the surrounding rock is poor with leads to strong support response. Thus, investigating the dynamic structural mechanical behavior of blocks is of great significance to the control of stope surrounding rocks in the western region. According to the dynamic structure formed by the relative rotation of key blocks, a kinematic mechanical analysis model is established. In this study, according to the change of geometric relationship between blocks, the relationship between the extrusion area and the angle of rotation is derived, and the dynamic process of the relative rotation of blocks is divided into three rotation stages. Based on the "voussoir beam" theory, the relationship between the extrusion force and the rotation angle of blocks in different stages is deduced, the structural stability and mechanical behavior are analyzed. Combined with the instability conditions, the working resistance of support is taken as the response characteristic, finding the most unstable position of the structure during the turning process, and then a method of calculating support working resistance is developed, and its correctness of the formula is proved by practical cases. The theoretical calculation results show that: with the increase of the rotation angle θ, the extrusion force T1 generally shows an increasing trend. When the blockness i<1, T1 increases or decreases in a quadratic parabola with θ change. However, when i>1, the curve gradually shows a linear change. As the blackness is large, the increase rate of T1 with θ is smaller. From the analysis of instability conditions, it can be revealed that the large key blocks are prone to slip instability in the early stage of rotation, but its anti-rotation deformation instability ability is relatively strong. For the characteristics of large blockness, weak self-stability of the structural and strong response of the support, it is necessary to design a reasonable support working resistance. By analyzing the stress conditions in the three rotation stages, it is found that the most unstable block is at the critical angle between the initial and middle rotation stage. Finally a formula of calculating the working resistance of support is given in the state of instability.

Key words: large key blocks, dynamic structure, extrusion area, stability analysis, response characteristics