## 3 Study on Migration Law of Overlying Strata in Deep Goal
### Simulation Analysis of Overlying Strata Migration in Goal
#### 3.2.2 Overburden Rock Migration Law  
(1) Vertical stress distribution characteristic under different advancing distance  
To study the development process of overburden rock migration law, the vertical stress cloud map during the working face advancing was first analyzed. It was found that the vertical stress range expanded with the continuous advance, as shown in Figure 10a-k. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Strata** & **Density/kg\(\cdot\)m\({}^{-3}\)** & **Bulk** & **Shear** & **Cohesion/MPa** & **Internal Friction** & **Tensile Strength/MPa** \\ \hline Medium sandstone & 2530 & 7.02 & 4.54 & 2.62 & 36 & 3.01 \\ siltstone & 2630 & 8.21 & 4.21 & 3.21 & 38 & 4.5 \\ sandstone & 2540 & 6.95 & 4.42 & 2.68 & 33 & 3.65 \\
32 \# coal seam & 1440 & 1.88 & 1.22 & 1.90 & 23 & 1.65 \\
33 \# coal seam & 1440 & 1.88 & 1.22 & 1.90 & 23 & 1.65 \\ Shale & 2430 & 3.42 & 1.72 & 2.11 & 30 & 2.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main mechanical parameters of rock strata. Figure 9: Numerical simulation model. In Figure 10a-i, with the increase in the advancing distance, the high vertical stress area always appeared in front of the working face. In addition, the maximum value of the high stress area gradually increases, indicating that the failure range of the overburden rock gradually expands, which shows that mining has a great influence on vertical stress distribution. Figure 10: Coal seam mining different distance vertical stress nephogram. (**a**) 10 m. (**b**) 20 m. (**c**) 30 m. (**d**) 40 m. (**e**) 50 m. (**f**) 60 m. (**g**) 80 m. (**h**) 100 m. (**i**) 120 m. (**j**) 180 m. (**k**) 240 m.  
By extracting the vertical stress data under different propulsion distances in Figure 11, the vertical stress curves under different propulsion distances can be obtained, as shown in Figure 11. Before the first square of the working face (0-120 m range), with the increase in the advance distance, the peak stress gradually increases from 22.3 MPa to 37.6 MPa, indicating that the larger the advance distance the easier the plastic failure occurs, and the stress concentration area gradually increases. When the advancing distance increases to 180 m (1.5 times the length of the working face), the peak stress decreases to 34.3 MPa. When advancing to 240 m (the length of the working face is 2 times), the peak stress of the advance abutment pressure is reduced to 33.9 MPa. To sum up, before the first square of the working face, with the increase in the advancing distance, the peak stress and its influence range are larger. Thus, the more serious the mine pressure near the working face is, the more attention should be paid to the advanced support; when the advancing distance exceeds the length of the working face, the overburden rock falls more fully, and the peak stress decreases slightly, indicating that the failure zone height reaches the maximum. (2) Plastic failure characteristic under different advancing distances  
To reveal the relationship between advancing distance and plastic failure field, the plastic failure characteristics of surrounding rock under different advancing distances are analyzed, as shown in Figure 12. With the increase in advancing distance, the plastic zone of the stope gradually increases. In especial, when the distance is half of the length of the working face, the plastic zone increases rapidly, and the plastic failure zone is slightly larger. At the same time, the plastic zone also develops to both of roof and floor, but the transmission degree of the roof is slightly larger than the floor. Before the first square of the working face, the development range of the plastic zone shows an evident increasing trend. When the working face advances to 60 m (half of the length of the working face), the height of the plastic zone reaches about 30 m. With the further increase in the advancing distance, the range of the plastic zone further expands.