## 3 Analysis of Results  
### Zonal Rupture Pattern of the Roadway Enclosure  
According to numerical simulation results, the development of the fracture planes of the surrounding rocks in the roadway followed the compression-shear conjugate fracture patterns of rock mechanics [18]. In the rectangular roadway after excavation, as shown in Figure 8, the shallow surrounding rocks became loose toward the roadway, and the stresses perpendicular to the roadway surface were gradually released. Accordingly, the shallow surrounding rocks underwent bidirectional compression. Therefore, the stress condition of the roadway could be reduced to a plane strain state. The stress conditions on the roof and the floor are shown in Figure 8 by ABCD, while AEFG corresponds to the stress conditions on both sides. When the horizontal \(\sigma_{\text{H}}\) and vertical \(\sigma_{\text{V}}\) stresses in the surrounding rocks exceeded the compressive strength value, conjugate failure occurred along the AM, GM, AN, and DN lines. After the conjugate fracture planes intersected, they formed an enclosed fracture loop MNOP in the surrounding rocks. The shallow surrounding rocks in the roadway were fractured and cut into wedge-shaped blocks by the fracture loop MNOP, as shown by the triangle AMG in Figure 8. Under high-stress conditions, the surrounding rocks could easily slip toward the roadway. After this loosening, the MNOP acted as a new roadway boundary: the stressed body under plane strain conditions (such as MUVN) continued to be isolated along each side of the MNOP. When the pressure \(\sigma_{\text{s}}\) exceeded the strength of the surrounding rocks, the conjugate shear fracture occurred, and a new fracture loop was formed outside the MNOP. Figure 7: Evolution of shear strain increment \(\Delta\gamma\) in the roadway-surrounding rock. (**a–e**) denote the rupture of each stage of the roadway model. According to the simulation results depicted in Figure 4, the nonuniform strength of the surrounding rocks can affect the development of the fracturing process. As shown in Figure 9, the roadway was located in soft rock strata, while its roof and floor were in hard rock strata. A comprehensive analysis of the simulation results presented in Figure 4 and the above fracture patterns revealed that the first and fourth layers of the fracture loops developed only in soft strata without penetrating the hard strata. With the expanding boundary of the loosening loop, the vertical pressures acting on the roof and floor gradually dropped. For example, during the process shown in Figure 6, the vertical stress variation along the  
Figure 8: Fracture expansion pattern in a high-stress soft rock roadway. Capital letters A,B,C,D,E,G,O,M,U,V,P denote geometric intersections. Figure 9: The expansion process of a fractured zone in the roadway with a strong-soft-strong composite surrounding rock. Capital letters A,B,C,D,E,F,G,H,IJ,K,L,M,N,O,P,Q,R,S,U,V denote geometric intersections. preset stress-monitoring line (Figure 7a) set up in the roadway floor occurred, as shown in Figure 10. After forming the second layer of the fracture loop, the mean vertical stress on the floor between the left and right boundaries dropped by approximately 40% compared with the value reached after the formation of the first layer of the fracture loop. After forming the first layer of the fracture loop, as shown in Figure 8, the stress on the floor within the range AB was close to zero, while both sides AI and BF were located in the stress-reduction zone. After forming the second layer of the fracture loop, the stresses within the AI and BF ranges further decreased. Accompanied by the decline in vertical pressure, the floor became prone to compression-shear failure. It was assumed that the roof and the floor reached their ultimate condition when the loosening fractured zones developed into OPQS. Afterward, the fractures developed towards the deep roof, the floor, and both sides in a compression-shear conjugate failure pattern.