# Cross-Section Shape and Asymmetric Support Technology of Steeply Inclined Thick Coal Seam Roadway
## 2 Engineering Background
### Analysis of Deformation and Failure of Roadways with Different Cross-Sectional Shapes
#### 3.2.2 Analysis of Numerical Simulation Results  
As shown in Figure 7, the plastic zones of the surrounding rock of the three cross-sectional shape roadways exhibit pronounced asymmetry. At the same time, affected by the differences in cross-sectional shapes and roadway bearing characteristics, large-area shear failures occur at the lower part of the lower side and the roof on the upper side, and the plastic zone range and depth reach the maximum at different positions of the sidewalls. The inclined-roof trapezoidal section exhibits the largest plastic zone area. Although the inclined roof conforms to the coal seam dip angle to reduce the shear effect between coal bedding planes, due to stress concentration, large-area plastic deformation and failure occur at the shoulder corners, with a maximum failure depth of 2.1 m, and more serious tensile failure occurs in the side roof under the condition of a larger roof length. The rectangular section ranks second in the plastic zone area. Under the combined action of shear slip between coal bedding planes and stress concentration, serious shear failures occur near the lower part of the lower side of the roadway and the shoulder corner of the upper side, with maximum failure depths of 1.5 m and 1.8 m, respectively. The arched section displays the smallest plastic zone area. Shear failures are mainly concentrated in the lower part of the lower side and the arching position of the upper side roof, with a maximum failure depth of 1.2 m. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Lithology** & **Density/kg\(\cdot\)m\({}^{-3}\)** & **Tensile Strength/MPa** & **Bulk Modulus/GPa** & **Shear Modulus/GPa** & **Cohesion/MPa** & **Angle of Internal Friction \(\phi\)/\({}^{c}\)** \\ \hline Mudstone & 2560 & 1.5 & 2.58 & 1.49 & 4.93 & 32.80 \\ \hline Silstone 2 & 2670 & 4.2 & 5.25 & 3.03 & 12.63 & 31.80 \\ \hline Sandy Mudstone & 2620 & 3.3 & 3.26 & 1.86 & 6.80 & 32.10 \\ \hline
5\#Coal & 1360 & 0.7 & 1.31 & 0.56 & 1.63 & 34.80 \\ \hline Silstone 1 & 2670 & 3.9 & 5.35 & 3.46 & 15.67 & 28.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: 1502 level roadway roof and floor physical and mechanical parameters. Figure 6: Numerical model of arched section roadway. In summary, under the mining conditions of steeply inclined thick coal seams, the three roadway cross-sectional shapes have their own characteristics. For the rectangular cross-section, it exhibits moderate overall stress distribution. Its most significant advantage lies in the ease of roadway formation and simple construction technology, as it requires no complex contour control or curved surface support. This can significantly reduce the technical difficulty of tunneling and construction costs, making it particularly suitable for engineering scenarios with high requirements for tunneling speed. However, this cross-sectional form has application limitations: due to its geometric shape, the rectangular cross-section forms a typical stress-concentration area at the shoulder angle (the junction between the roof and sidewalls). This phenomenon originates from the action of asymmetric surrounding rock stress--after roadway excavation, sudden changes in boundary conditions at the shoulder angle cause stress redistribution, where vertical and horizontal stresses overlap to form stress peaks higher than those in the surrounding rock mass. If the surrounding rock is of low strength or poor integrity, stress concentration at the shoulder angle is prone to induce local rib spalling, roof collapse, and other instability phenomena. This stress-concentration effect becomes more severe in high-ground-stress environments or areas with large rock layer dips. Therefore, this cross-section is suitable for roadway projects with simple geological conditions (e.g., near-horizontal strata, good rock integrity), mild stress environments, and priority given to construction efficiency.