## 5 Numerical Simulation of Super-Large-Section Roadway Excavation  
The driving face in the No. 210 mine roadway with super-large sections was taken as the engineering background for a 3D numerical simulation model, which was established as shown in Figure 9. FLAC3D 7.00 numerical simulation software was adopted to study both stress distribution laws and deformation and failure behaviors concerning the surrounding rock of unsupported rectangular roadways with super-large sections. In order to mitigate the influence of the boundary effect, the design model was 100 m in length along the strike, 100 m in dip length and 52.5 m in height. The model was divided into 450,200 units and 465,681 nodes. The Mohr-Coulomb constitutive model was adopted for the stratum, and its parameters were assigned according to the values given in Table 4. The roadway had a buried depth of 200 m, its bulk density \(\gamma\) was 25 KN/m\({}^{3}\), and both the perimeter and bottom of the model were subject to fixed constraints. In light of the requirement for calculation accuracy, mesh encryption was applied upon surrounding rock near the excavation zone of coal pillars between coalfaces. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **Data Sources** & \multicolumn{3}{c}{**Document [26]**} & \multicolumn{3}{c}{**Document [24]**} \\  & **b/h** & & **1.4** & **2.2** & **1.8** & **3.2** & **5.0** \\ \hline \multirow{4}{*}{\(\lambda\)} & \multirow{2}{*}{literature results} & \(\lambda_{\text{up}}\) & \textgreater{}2.0 & \textgreater{}2.0 & 2.0–2.5 & 2.5–3 & 3–4 \\  & & \(\lambda_{\text{down}}\) & 0.5–1 & 0.5–1 & 0.5–0.7 & 0.7–0.8 & 0.8–0.9 \\  & & \(\lambda_{\text{up}}\) & 2.000 & 2.334 & 2.083 & 2.786 & 3.689 \\  & & \(\lambda_{\text{down}}\) & 0.600 & 0.676 & 0.621 & 0.742 & 0.814 \\  & & \(\lambda_{\text{up}}\) & 1.984 & 2.341 & 2.161 & 2.805 & 3.691 \\  & & \(\lambda_{\text{down}}\) & 0.600 & 0.662 & 0.631 & 0.728 & 0.817 \\ \hline \end{tabular}
\end{table} 
Table 3: Calculation results of side-pressure coefficient range. Figure 9: Numerical simulation of three-dimensional model. Influence of Aspect Ratios on Deformation and Failure of Surrounding Rock in Rectangular Roadways with Super-Large Sections  
In order to study the influence of the width of the roadway with super-large sections upon the deformation and failure of surrounding rock, four groups of models were designed with their roadway widths as 15 m, 20 m, 25 m and 30 m; the height as 2.5 m; the side-pressure coefficient \(\lambda\) as 1; and the buried depth as 200 m. The numerical simulation results were as follows: With different aspect ratios, the perpendicular stress field cloud map concerning the surrounding rock of excavated roadways was generated, as shown in Figure 10. Moreover, the displacement degrees were measured, as shown in Figures 11 and 12. Finally, the plastic zones were charted, as shown in Figure 13.  
After roadway is excavated, the perpendicular stress surrounding the driving face is redistributed and a large stress concentration takes place on the side walls of the roadway. As there are different roadway widths, the perpendicular stress upon the side walls of the roadway increases first, then decreases and eventually tends to stabilize. When roadway widths were 15 m, 20 m, 25 m and 30 m, the values of the maximum stress upon the two side walls were 7.14 MPa, 7.77 MPa, 8.32 MPa and 8.61 MPa, respectively, and the stress concentration coefficients were 1.43, 1.55, 1.66 and 1.72, respectively. The larger the roadway width, the greater the vertical stress upon both side walls of the roadway. Moreover, low-stress areas will be generated on the roadway's roof and base plate. As the roadway width increases, the overhanging roof length increases, the roof becomes even more susceptible to bed separation and roof caving and a low-stress area also develops on the roof accordingly.