## 5 Research Result
### Analysis of Instability Characteristics of Surrounding Rock in Roadway  
According to the theory of elastic-plastic rock [33], a mechanical model of the roadway roof is built. The original rock stress is located is the x\({}_{0}\)y\({}_{0}\) coordinate system, and the roadway roof is considered as a fixed beam supported by the rock mass at both ends, as indicated in Figure 12. The h denotes the thickness of the rock beam, and the load on the overlying rock layer is \(q=\gamma h\); the inclination angle of the top plate is \(\alpha\). For the convenience of analysis, the overlying rock load on the roof is decomposed into \(q_{x}=qsina\) and \(q_{y}=qcosa\). For the roadway roof, \(q_{x}\) mainly exerts axial compression. According to material mechanics, when the settlement of the roadway roof is small, \(q_{x}\) has little contribution to the bending moment of the roof, and \(q_{y}\) is key to the stability of the roof. In view of this, the following analysis of the roof mechanics model still projects the force in the direction of the vertical roof and the direction of the roof inclination and takes the load \(q_{y}\) of the vertical roof as the research object.  
Due to the large dip angle of the coal rock layer, the gravity of the rock can be segmented into a component \(q_{y}\) perpendicular to the bedding plane and a component \(q_{x}\) along the bedding plane, as shown in Figure 13.  
Figure 12: Mechanical model of roadway roof.  
Figure 13: Instability characteristics of surrounding rock in nearly vertical coal–rock-interbedded roadway.  
From the left rib of the roadway, it acts on the left rib along the vertical bedding plane direction. When it is from the upper right rib of the roadway, it acts on the right rib along the bedding plane direction. Because the rock layer has a large inclination angle, the force of gravity along the bedding direction of the coal rock layer increases. Because of that, the coal seam and its adjacent parts of the rock layer are relatively soft; the structural planes are relatively developed. Consequently, the soft coal seam and rock mass are prone to severe dislocation deformation, resulting in the rock mass sliding along the bedding plane and the subsidence of the roadway roof rock layer. Owing to the lithology of the roadway floor, the strength of the coal-rock interbedding is relatively low, and serious floor heave under the effect of tectonic stress will consequently occur;
2. When the thickness of the coal rock layer is small, the coal rock layer is similar to a longitudinal bending instability structure where the upper and lower ends are constrained and vertically compressed. The stress on the left and right sides and the roof are different, so the displacement of the roof on one side of the roadway is large, which is easier for bulging deformation;  
In summary, the asymmetric distribution of stress in the surrounding rock of the nearly vertical coal-rock interlayer roadway causes deformation and failure of the roadway-surrounding rock. There is obvious asymmetry or imbalance within the same cross-section because of the large deformation of the surrounding rock near the roadway and floor. The possible reason for this phenomenon is that the surrounding rock is sustained to significant asymmetric loads. Moreover, the poor lithology of the surrounding rock makes shear dislocation prone to occur between interbedded rock layers.