# Stability and Force Chain Characteristics of \"Inclined Step Cutting Body\" in Stope
## 3 Results  
### Morphological Characteristics of Overburden Caving  
In the process of the working face advancing, the overlying strata will be affected by different degrees of mining, and the corresponding movement and deformation will occur. Figure 4 shows the evolution of overlying strata collapse in the process of the working face advancing. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Symbol** & **Description** & **Loess Layer** & **Silstone** & **Mudstone** & **Coal** & **Gritstone** \\ \hline \(\gamma\) (KN/m\({}^{3}\)) & Volume-weight & 17 & 24 & 24 & 14.2 & 25.1 \\ \(R\)(cm) & Minimum radius of particles & 20 & 20 & 20 & 20 & 20 \\ \(R_{\rm max}/R_{\rm min}\) & Particle Radius Ratio & 1.6 & 1.6 & 1.6 & 1.6 & 1.6 \\ \(E^{*}\) (GPa) & Effective modulus of flat joint & 0.42 & 31.24 & 13.62 & 4.24 & 19.72 \\ \(K^{*}\) & Rigidity ratio of flat joint & 2 & 2 & 2 & 2 & 2 \\ \(\sigma_{c}\) (MPa) & Average tensile strength and standard deviation of flat joints & 0.1/0.025 & 1.8/0.5 & 0.8/0.2 & 0.25/0.0625 & 1.1/0.275 \\ \(c\) (MPa) & Average cohesion and standard deviation of flat joints & 4/1 & 20/5 & 20/5 & 10/2.5 & 20/5 \\ \hline \hline \end{tabular} Note: In other numerical models, \(E\) generally represents the elastic modulus, and \(K\) generally represents the bulkmodulus. In order to distinguish these similar symbols, this paper uses \(E^{*}\) to represent the effective modulus of flatjoint and \(K^{*}\) to represent the rigidity ratio of flat joint.  
\end{table} 
Table 2: Micromechanical parameters of strata. Figure 3: Numerical model. The working face is advanced along the uphill direction from the open cut. When the coal seam is mined 80 m, the first saving occurs in the working face, and the caving height is 17.3 m. The development is terminated in the S3 strata, and the collapsed rock blocks are stacked on the coal seam floor. At this time, the mining fractures are mainly distributed in the S2 strata and are separated from the S3 strata. When the coal seam is mined 96 m, the sliding motion of the S2 rock strata due to shear failure leads to sliding instability, forming a \"cutting body\". When the coal seam is mined 160 m, 200 m and 248 m, periodic caving appears in the overlying strata, periodic caving step distance is 40-48 m, the surface is accompanied by periodic cracks, mainly existing in the top of the working face and the boundary. Due to the shallow depth of the coal seam, the surface cracks eventually connect with the working face, forming a penetrating mining crack. The surface is characterized by step failure, resulting in the formation of rock pillars. According to the simulation results, it is found that, at the coal mining stage, the overburden failure is ladder-shaped, and the roof will form a \"inclined step cutting body\" structure, which is prone to sliding instability, as shown in Figure 4. According to the analysis, the overlying strata produced the whole inclined shear fracture in the mining process of a 22,021 working face. Under the influence of its own gravity and coal mining factors, the blocks formed after the fracture are prone to slide and cause instability of the overall structure. The blocks formed after the shear fracture of the overlying strata are called the \"cutting body\". The structure formed by the interaction of the \"cutting body\" is the \"inclined step cutting body\" structure. Due to the poor bearing capacity of the structure, with the sliding instability, the overburden movement produces more load on the support. At this time, the overlying load is fully transmitted, resulting in severe pressure on the working face, and it is prone to  
Figure 4: Rock caving patterns at different advancing distances. roof fall accidents. The structure reasonably explains the phenomenon of safety accidents in shallow coal seam mining. Real-time monitoring on the surface is conducted before the excavation.