# Stability Assessment of Gob Side Entry at the Steeply Inclined Mining Face
## 2 Materials and Methods
### Brief of the Case  
The research subject is the 3308 track entry from Yangcheng Coal Mine at Jining, Shandong Province. The layout of researched mining face is shown in Figure 1. The 3308 mining face is situated deep within the third mining area and is next to the 3306 goat. The mean thickness of coal is 7.5 m. The mining face inclination ranges from 23\({}^{\circ}\) to 27\({}^{\circ}\), with an average of 25\({}^{\circ}\). The coal seam is directly overlain by siltstone with a thickness of 3.8 m. The upper layer consists of fine sandstone, about 17.1 m in thickness. The pseudo-bottom consists of mudstone, with a thickness of 1.6 m. The coal and roof has a pronounced impact tendency. The floor shows a modest impact tendency. During construction, minor impact phenomena from the coal cannon may arise. The 3306 belt entry is positioned within coal and is excavated along the floor. The roadway has a rectangular cross-section, and the excavation dimensions are 5.0 \(\times\) 3.4 m.  
The 3308 track entry is subjected to severe stress, resulting in the deterioration of surrounding rock. Four elements are outlined based on the evaluation results of geomechanical properties. By considering the geological parameters and engineering conditions, the stability of the rock mass around the gob side driving roadway in the significantly inclined mining face is comprehensively analyzed.  
(1) Buried Depth  
The mining face elevation is \(-\)780\(--\)960 m, and the ground elevation \(-\)35.9\(\rightarrow\)38.9 m. The coal mine is located in a plain area, with the flat surface of villages and farmland. The maximum buried depth of the mining face is close to 1000 m. The most important feature of deep mining is high stress, which further contributes to nonlinear stress characteristics of rock. The buried depth condition leads to the enhanced effect of surrounding rock disturbance and the increased difficulty of control.  
Figure 1: Layout of 3308 mining face (unit: m).  
Strata Thickness and Lithology  
The average thickness of coal is 7.5 m. The mining face is made of fully mechanized discharge mining. The roof movement in the process of extraction is relatively strong. The main roof is a fine sandstone of 17.1 m thick. After the mining of the 3306 face, the thick and hard roof forms a cantilever beam structure at the lateral boundary of the goat, which provides certain cover for the excavation of the 3308 track entry. However, during the mining period of the 3308 face, the sandstone roof is not easy to break, causing high pressure at the lateral boundary. The immediate floor is mudstone, 1.6 m thick. The floor strength is low, leading to a large deformation tendency. The burial depth and lithology conditions of the engineering case show that the mine pressure is strong during the extraction process.  
Geological Structure and Tectonic Stress  
The mining region is intersected by several faults, and coal extraction is influenced by intricate geological formations. The stress within the fault structure is concentrated, and the stress environment of the adjacent rock is intricate.  
Stratigraphic Dip  
The mean formation inclination is 25\({}^{\circ}\). The mining face 3308 is situated beneath the 3306 goat in the inclined direction. Subsequent to the coal seam at the 3306 mining face, the roof has a tendency to subside and shift towards the goat. At significant inclination degrees, the coal pillar experiences compression and shear forces. The stress distribution of the pillar is intricate. The force of surrounding rock is uneven. If the conventional symmetry anchor network support technology and process are adopted, the stability of the roadway cannot be effectively controlled.