## 5 Results
### Different Drift Ratio  
The double-side drift method is commonly used in the construction of large-span highway tunnels to divide into smaller sections through sequential excavation. This study analyzed the control effect of the surrounding rock stability using numerical calculations for drift ratios of 0.20, 0.25, 0.30, 0.30, and 0.45. To enable a comparison of the impact of the left and right drifts on the surrounding rock pressure of the middle drift, while keeping other factors constant, the tunnel excavation size, physical and mechanical parameters of the surrounding rock, and supporting structure are consistent with the test section. The ratio of the left and  
The simulation results of the tunnel arch settlement were analyzed. It was found that both point 0 and point 1 are sinking and changing, while point 2 shows uplift. A comparison was made between the simulation results of different drift ratios. When the ratio of the drifts on both sides is less than 0.3, as the proportion of drifts on both sides increases, the arch settlement of point 0 and point 1 also increases significantly, while the uplift deformation of point 2 decreases, and the change is small. When the ratio of the drifts on both sides exceeds 0.3, with an increase in the proportion of drifts on both sides, the settlement of the arch at point 0 and point 1 continues to gradually increase, and the change is small. Additionally, the uplift and deformation of point 2 is also gradually increasing, with a relatively large change range. When comparing the drifts on both sides, if they are small, the settlement of the deep side and the middle drifts is large, and it is heavily affected by the percentage of drifts on either side. Conversely, if the drifts on both sides are small, the deformation of the shallow side is small, and it is less affected by the percentage of drifts on either side. When the percentage of drifts on both sides is large, the deformation of deep side and middle drifts is less affected by the percentage of drifts on both sides, while the deformation of shallow side drifts is more affected by the percentage of drifts. As shown in Figure 13b, it is evident that the horizontal convergence of the arch foot is greater than that of the arch waist. The horizontal convergence shows a trend of gradual increase with the increase in the ratio of drifts on both sides, and the greatest increase in convergence is observed when the ratio of drifts on both sides is between 0.25 and 0.35. Figure 14 illustrates the vertical stress contours of the initial support structure with different drift ratios. The contours reveal compressive stresses are evident at the sidewalls of the initial support, while tensile stresses are evident at the tunnel arch and the inverted arch. The highest principal stresses are located at the foot of the arch on the deeply buried side, characterized by compressive stresses. The initial support experiences a maximum compressive stress of 9.10 MPa and a maximum tensile stress of 1.08 MPa when the ratio of the drifts on both sides is 0.2. As the ratio increases, both compressive and tensile stresses decrease. At a ratio of 0.3, the maximum compressive stress drops to 8.67 MPa and the maximum tensile stress decreases to 0.85 MPa. Subsequently, as the ratio of drifts on both sides is 0.4. Figure 15: Comparison of plastic zone: (**a**) the ratio of the drifts on both sides is 0.2; (**b**) the ratio of drifts on both sides is 0.25; (**c**) the ratio of the drifts on both sides is 0.3; (**d**) the ratio of the drifts on both sides is 0.35; (**e**) the ratio of the drifts on both sides is 0.4.  
sides further increases, the compressive stress rises while the tensile stress continues to decrease. When the ratio reaches 0.4, the maximum compressive stress peaks at 9.54 MPa, and the maximum tensile stress drops to 0.44 MPa. This trend indicates that the initial support's compressive stress initially decreases and then increases with the ratio of the drifts on both sides.