## 6 Stability Control and Assessment of Gob-Side Entry
### Deformation Characteristics of Gob-Side Entry  
In order to obtain the deformation characteristics of the surrounding rock of the track roadway during excavation along the goat, a simulation calculation model was established by using the simulation software Fast Lagrangian Analysis of Continua (FLAC 3 D 6.0) according to the geological conditions of 1321 (1) working face and 1331 (1) track roadway. The size of the model is 343 m long, 300 m wide, and 172 m high, with a total of 825,346 units. The bottom boundary of the model is fixed, the left and right boundary limits the horizontal displacement, and the top boundary imposes self-weight stress. The simulated coal-seam mining height is 2 m, and the simulated roadway size is 5.4 m wide and 3.6 m high. Coal and rock mass can be regarded as elastic-plastic material, which is simplified to elastic-plastic model in numerical calculation, and Molar-Coulomb failure criterion is selected. The working face was simulated by advancing 10 m each time, and the roadway was simulated by excavating 10 m each time. The numerical calculation model is shown in Figure 21, and the physical and mechanical parameters of coal and rock are shown in Table 5.  
Simulation process: initial ground stress balance \(\rightarrow\) 1321 (1) waking face \(\rightarrow\)1331 (1) track roadway \(\rightarrow\) output result. The equilibrium condition is reached when the geo-stress is calculated to 8430 steps, and the maximum unbalance force is less than 1 \(\times\) 10\({}^{-5}\). The average geo-stress of coal seam and roadway is 21.3 MPa, and the geo-stress is generally distributed horizontally. Figure 21: Stress-balance cloud map of primary rock. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Rock** **Straum** & \begin{tabular}{c} **Density** \\ **d/kg.m**\({}^{-3}\) \\ \end{tabular} & \begin{tabular}{c} **Bulk Modulus** \\ **K/GPa** \\ \end{tabular} & \begin{tabular}{c} **Shear Elasticity** \\ **G/GPa** \\ \end{tabular} & \begin{tabular}{c} **Frictional Angle** \\ **\(\varphi/^{c}\)** \\ \end{tabular} & \
\begin{tabular}{c} **Adhesion Stress** \\ **C/MPa** \\ \end{tabular} &
\begin{tabular}{c} **Strength of** \\ **Extension** \\ **u/MPa** \\ \end{tabular} \\ \hline Fine sandstone & 2650 & 9.5 & 5.6 & 38 & 5.2 & 5.5 \\ \hline Mudstone & 2430 & 4.6 & 2.5 & 33 & 3.5 & 1.5 \\ \hline Coal & 1350 & 3.5 & 1.2 & 28 & 1.2 & 0.5 \\ \hline Mudstone & 2400 & 4.5 & 2.5 & 33 & 3.5 & 1.4 \\ \hline Silstone & 2750 & 9.8 & 5.6 & 36 & 5.5 & 5.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Physical and mechanical parameters of coal and rock. After the mining of 1321 (1) waking face, 1331 (1) track roadway was excavated. The displacement changes in roadway surrounding rock of track roadway under different excavation distance conditions were shown in Figure 22.  
According to the analysis of the above figure, under the influence of residual mining stress of adjacent working face and disturbance during roadway excavation, the displacement of surrounding rock is mainly concentrated on both sides and the roof and floor of the roadway during roadway excavation. With the increase in excavation distance, the displacement of overlying rock gradually increases and tends to be stable, while the floor-heave phenomenon occurs in the underlying rock in a small range. When the roadway is driven to 50 m, the maximum displacement variation in the roof and floor of the roadway is about 81 mm. When the roadway is driven to 100 m, the maximum displacement change in the roof and floor is 88 mm. When the roadway is driven to 150 m, the maximum displacement change in the roof and floor is 95 mm, and when the roadway is driven to 200 m, the maximum displacement change in the roof and floor is 97 mm. In the direction of inclination, with the excavation of the roadway, the displacement changes in the stratification phenomenon appear on both sides of the roadway.