## 3 Numerical Model and Simulation Scheme of the Strain-Structural Plane
### Characteristics of Fracture Information  
Figure 6 is the cloud diagram of fracture propagation under different conditions in the surrounding rock. In the figure, the black and grey lines are the displacement of joints, which can characterize the fracture propagation characteristics of rock mass. The extension range of black and grey lines is the fracture propagation range. The deeper the color, the greater the displacement of joints. The fracture information of surrounding rock under different conditions is analyzed, respectively, and the variation laws are as follows.  
Observing Figure 6a-c, the influence of \(\theta\) on the fracture propagation is mainly reflected in two aspects: on the one hand, the fracture propagation range at the vault increases, the fracture propagation range at the right spandrel decreases, while the fracture propagation range of the right sidewall increases, and the fracture propagation is close to symmetrical distribution. On the other hand, \(\theta\) with a larger value will increase the fracture width, indicating that the angle has a significant effect on the fracture propagation direction, propagation degree, and fracture width of surrounding rock. Observing Figure 6d-f, when \(L\) = 6.5 m, the distribution of fracture propagation is approximately symmetrical. When \(L\) = 8.5 m, the rock fracture propagation is greatly affected by the structural plane. The fracture propagation range formed between the upper tip of the structural plane and tunnel increases, and the fracture opening degree of the structural plane tips also increases, while there is no obvious fracture propagation outside the structural plane tips. The fracture propagation range at the structural plane tips increases along the plane direction.  
When \(L=10.5\) m, the fracture propagation range of the above two parts further increases. Observing Figure 6g-i, when \(D=0\) m, only the fracture propagation range at the vault and left arch foot is small, and the fracture propagation in other parts is obvious. When \(D=1.7\) m, the fracture propagation at the structural plane tips is obvious, and the rock mass below the plane has a larger propagation range along the plane. The rock mass above the plane extends shorter along the plane, but the fracture propagation depth is larger. Compared with \(D=0\) m, the fracture propagation range of the vault increases under this condition, while the fracture propagation at the right arch foot decreases. When \(D=3.4\) m, the difference in fracture propagation characteristics of rock mass on both tunnel sides further reduces, showing the characteristics of the approximate symmetrical distribution. The fracture propagation mainly occurs at the arch bottom and side wall. The fracture propagation range and degree at the vault are small, and the fracture propagation range above the structural plane is large. The above results show that as \(D\) increases, the fracture propagation range and fracture displacement decrease, especially near the structural plane, indicating that the structural plane effect on fracture information gradually weakens, and when \(D\) is small, the fracture displacement color is deeper, that is, the fracture opening degree is larger. As the relative distance increases, the color of the fracture displacement is lighter, and the fracture opening degree decreases.