# 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
For the arched cross-section, a mechanical analysis shows that the arched cross-section has the optimal stress distribution characteristics, with significantly lower stress concentration coefficients in the vault and arch shoulder areas compared to other cross-sectional forms. This mechanical advantage stems from the axial load-bearing characteristics of the arched structure, which can effectively mobilize the self-supporting capacity of the surrounding rock and reduce the load on the support structure. In steeply inclined thick coal seams (coal seam thickness > 3.5 m or coal seam thickness > roadway height) where the entire cross-section is located in soft coal (uniaxial compressive strength \(\leq\) 15 MPa), the arched cross-section can significantly improve the stress state of the surrounding rock and exhibit good engineering adaptability. However, this cross-sectional form also has limitations: when the coal seam thickness is <3.5 m, part of the cross-section may be located at the coal-rock interface, where shear slip failure is prone to occur due to interlayer shearing action. In addition, when the excavation direction changes or the burial depth increases, the arch shape may lose its advantages over other cross-sectional shapes. Based on numerical simulation studies and numerous research results, combined with the specific engineering conditions of the 1502 level roadway (steeply inclined thick coal seam, soft coal occurrence), the arched cross-section was ultimately determined to be the optimal form  
For the inclined roof trapezoidal cross-section, the roadway roof of the inclined roof trapezoidal cross-section is excavated along the coal seam bedding, preserving the original bedding structure of the coal seam, and the inclined roof structure conforms to the force of  
Figure 7: Plastic zone state of roadway surrounding rock with three types cross-sectional shapes in steep seam. the inclined coal-rock layers. This structural feature brings significant mechanical advantages: it can suppress the generation of interlayer shearing action and effectively control the deformation of both sidewalls. However, this cross-sectional form has application limitations: it requires stable bedding within the coal seam as a precondition, and the longer roof is more prone to failure, resulting in lower cross-sectional utilization. In terms of the stress-distribution characteristics, significant stress concentration occurs at the corner angles of the sidewalls, triggering stress field redistribution in the ribs--stress decreases in the upper rib and increases in the lower rib. The specific mechanism is as follows: due to the smooth bedding planes, shear stress redistribution under gravitational force in the lower rib coal body causes the failure mode to shift from slip failure to shear deformation. While this enhances the local bearing capacity, it leads to deep expansion of the plastic zone. The upper rib coal-rock, driven by continuous gravitational component forces, accumulates slip potential energy along bedding planes, making it prone to coal body instability and (sliding collapse), which can trigger surrounding rock failure. Therefore, the inclined roof right trapezoidal cross-section is suitable for thin and medium-thick coal seams (0-3.5 m) excavated along the roof. Deformation and Failure Mechanism of Surrounding Rock in Roadways Under Different Coal Seam Dip Angles  
For steeply inclined thick coal seam roadways, in addition to the roadway cross-sectional shape, the coal seam dip angle is also an important factor affecting roadway deformation and failure. Numerical simulation models of arched roadways with coal seam dip angles of 0\({}^{\circ}\), 10\({}^{\circ}\), 20\({}^{\circ}\), and 30\({}^{\circ}\) were established. Except for the coal seam dip angle and related strata structural changes caused by the dip angle variation, all other model parameters are consistent with those of the arched roadway numerical simulation model with a coal seam dip angle of 42\({}^{\circ}\).