# Analysis of the Interaction Effects of Shield Structure Oblique Passing under an Existing Tunnel
## 7 Conclusions and Discussion  
This article investigates the interaction effects of double-lane shield tunnels obliquely passing under existing tunnels. Numerical simulation calculations are undertaken for comparison with the measured data for analysis and research. The results of this study show that the internal forces and displacements generated in the existing tunnel during the shield underpass are within a safe range, and the ground settlement also meets the  
Figure 21: Maximum settlement increment ratio of the existing tunnel under different construction stages. Figure 22: Longitudinal rotation index of the existing tunnel with different spatial intersection angles. construction settlement control requirements (<10 mm), thus confirming the applicability of the shield method in the Guiyang area and providing a reference for similar projects in the future. Further analysis conducted using numerical simulation software led to the following conclusions:  
* After the completion of the RT excavation in Line 3, a settlement trough with a width of about 45 m was formed on the ground surface above the existing tunnel axis. When the excavation of Line 3 LT was completed, the settlement trough became wider and deeper, with the maximum settlement value occurring along the center line of the new two-lane tunnel. Figure 7 shows that the value of the settlement data measured in the field is significantly larger than the calculated value. Furthermore, considering the hardening process of grouting will cause the calculated results to more closely match the values measured in the field. * During this period of LT excavation after the completion of RT excavation, the maximum settlement point above the existing tunnel gradually moved first from the right side above the RT to directly above the RT center line and finally to directly above the center axis of the two-lane tunnel. Additionally, the surface settlement curve obtained considering the grout hardening process was not as smooth as the curve obtained when this process was not considered. * Changes in the pressure of the surrounding rock acting on the tunnel will lead to changes in the deformation of the tunnel and its corresponding internal forces (axial forces and bending moments). The lateral deformation of the existing tunnel during RT and LT excavation showed the same pattern, and the RT excavation caused the lateral deformation of the existing tunnel to be larger. When the new two-lane tunnel passed through the existing tunnel, the three sections of the existing tunnel lining gradually changed back to their original shape. Only two sections of the lining were tilted to the left and right side of the deformation, and the internal forces of the existing tunnel were in the envelope, meaning that the existing tunnel will not experience large torsional deformation. * In contrast to vertical underpasses, double-lane shield tunneling that obliquely underpasses existing tunnels will cause the irrecoverable local torsional deformation of the existing tunnels. The distribution pattern of the existing tunnel rotation index \(\omega\) was similar for RT and LT after excavation completion, and the existing tunnel rotation caused by LT excavation was larger than that caused by RT excavation. The rotation range of the existing tunnel caused by the shield underpass in this paper was \(-0.70\times 10^{-6}\sim 1.80\times 10^{-6}\). * The settlement of the existing tunnel vault and arch bottom caused by the excavation of the new shield tunnel was greatly influenced by the spatial intersection angle \(\beta\). As the spatial intersection angle \(\beta\) increased from 0\({}^{\circ}\) to 90\({}^{\circ}\), the minimum settlement of the existing tunnel vault and arch bottom appeared at \(\beta=90^{\circ}\); the maximum settlement occurred at \(\beta=0^{\circ}\); and the maximum change in settlement at the vault and arch bottom positions was 2.06 mm and 2.44 mm, respectively, showing increase ratios of about 341.4% and 317.5%.