## 5 Simulation Analysis of Support Effectiveness
### Stress Analysis of the Roadway Perimeter Rock  
Figure 6 illustrates the distribution characteristics of the maximum principal stress, minimum principal stress, and vertical stress (z-direction) in the surrounding rock under two working conditions: without support and with anchor net shotcrete support.  
Figure 6: Diagram of stress distribution before and after support. **(a)** Decreasing trend of maximum principal stress before and after support, **(b)** decreasing trend of minimum principal stress before and after support, **(c)** decreasing trend of vertical stress before and after support.  
Under unsupported conditions, stress concentration is primarily observed in the shoulder area of the roadway and at the base of the sidewalls. The maximum principal stress reaches 16.90 MPa, concentrated at the roadway shoulders, indicating that this zone experiences high compressive stress due to excavation-induced disturbance and is, thus, prone to compressive shear failure. The minimum principal stress is concentrated near the floor, exhibiting tensile characteristics, which may lead to tensile failure of the rock mass. The maximum vertical stress is 10.25 MPa, and although its distribution is relatively uniform, localized concentration is still present at the junction between the roof and floor, potentially causing structural stress imbalance.  
With the application of the anchor net shotcrete support, the stress distribution within the surrounding rock improves significantly. The maximum principal stress is reduced to 14.23 MPa, reflecting a 15.8% decrease, and the extent of the stress concentration zone is markedly reduced. This indicates that the support system effectively redistributes and alleviates the high compressive stress at the roadway shoulders, thus mitigating the risk of localized failure. Additionally, the range of tensile stress is significantly reduced, with the minimum principal stress increasing, suggesting that the support system suppresses tensile stress development, particularly at the wall bases. The maximum vertical stress decreases to 7.74 MPa, a reduction of approximately 24.5%, and its distribution becomes more uniform, which facilitates the maintenance of overall stress equilibrium in the surrounding rock mass.  
From a mechanical perspective, the anchor rods link the shallow fractured rock with the deeper stable strata, thereby enhancing the structural integrity and overall load-bearing capacity of the surrounding rock. Meanwhile, the shotcrete layer and steel mesh rapidly seal surface cracks, restrict deformation and crack propagation, and inhibit the formation of new stress concentration zones. As a result, the stress within the surrounding rock is redistributed more uniformly, and localized high-stress regions are effectively weakened, significantly improving the stability and safety of the roadway.  
In summary, the anchor net shotcrete support exhibits a notable capacity to relieve local stress concentrations and optimize the stress distribution in the surrounding rock, providing a critical safeguard for the long-term stable performance of the roadway structure.