## 4 Results and Discussion
### Stress Evolution Characteristics  
The evolution of coal seam roof stress under the influence of factors such as roof drenching, irregular surfaces, and mining is analyzed, as illustrated in Figure 8. The key findings are summarized as follows:  
1. Influence of irregular surfaces: The presence of a \"T\"-shaped irregular surface induces significant alterations in the distributions of maximum principal stress and maximum shear stress. The maximum principal stress concentration occurs beneath the \"T\" surface and outside its connection, with a small stress reduction area observed at the intersection of the \"T\". The maximum shear stress is concentrated within the \"T\" channel due to the compression of adjacent rock layers. The vertical stress distribution is influenced by the thickness of the overlying rock layers, revealing a stress reduction zone on the \"T\" surface and concentration zones in higher terrains and at the bases of slopes. 2. Influence of mining: In the initial stages of mining, there is no significant impact on the distribution of maximum principal stress. However, as mining progresses, areas of maximum principal stress concentration develop in both the advanced and lagging stages of the working face, with peak values increasing. The extent of this concentration is contingent upon the mining distance, with larger ranges observed at 50 m, 90 m, and 140 m from the working face. 3. Post-mining shear stress: Following mining operations, maximum shear stress concentration is evident around the goal area and the advanced section of the roadway. Within a range of 10 m to 90 m from the mining site, the shear stress in the roadway roof is significantly elevated compared to other areas, reaching a maximum of approximately 2.19 MPa. 4. Vertical stress distribution: Consistent zones of vertical stress concentration are identified around the working face. A stress reduction zone forms above the roadway roof after the advancement of the 51,102 working face by 90 m, coinciding with the influence zone of the \"T\"-shaped surface. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Split Tensile Test** & \multicolumn{3}{c}{**Uniaxial Compression Test**} \\
**Water Content (\%)** & **Tensile Strength** & **Uniaxial Compressive Strength (MPa)** & **Elasticity Modulus (GPa)** & **Poisson’s Ratio** & **Shear Modulus (GPa)** \\ \hline
0 & 4.18 & 86.12 & 0.91 & 0.25 & 0.37 \\
1.25 & 3.81 & 62.26 & 0.73 & 0.24 & 0.29 \\
2.5 & 3.12 & 55.13 & 0.59 & 0.24 & 0.24 \\
3.5 & 2.61 & 32.06 & 0.54 & 0.23 & 0.22 \\
5 (saturated) & 2.14 & 27.57 & 0.47 & 0.23 & 0.19 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of physicochemical parameters of coarse-grained sandstone. Figure 9 illustrates that following the excavation of the two roadways associated with the 51,102 working face, the mining activities at the 51,102 working faces did not impact the distribution of maximum principal stress and vertical stress in the roof of the roadways. Both distributions remained consistent, with only minor alterations observed in the openings of the roadway and the position of the open-off cut. Figure 8: The cloud map of stress distribution at different mining distances of 51,102 working face: (a) 0 m, (b) 10 m, (c) 40 m, (d) 90 m, (e) 140 m, (f) 160 m.  
Prior to the excavation of the roadway, a zone of maximum shear stress reduction was identified beneath the \"T\" corner position. Following the completion of the two roadways, a relatively high maximum shear stress was observed within 10 m both in front of and behind the opening, with the maximum shear stress concentration occurring approximately 8 m behind the open-off cut. Before the mining of 90 m of the working face and prior to reaching the surface of the \"-\" section, fluctuations in the maximum shear stress of the roof were noted. However, the trend of maximum shear stress at the face remained consistent across varying mining distances. It was observed that as the distance of the face mined increased, the value of the maximum shear stress also rose.