# Analysis of Shield Tunnels Undercrossing an Existing Building and Tunnel Reinforcement Measures
## 4 Model Validation
### Effect of Successive Excavation of Double Shield Tunnels on Mechanical Behaviors of Building  
Using excavation distance as the horizontal coordinate, the effects of double shield tunnel excavation on the mechanical properties of the building were studied. Figure 20 shows the variation of building subsidence and lateral displacement of piles (in the direction of shield excavation) with excavation distance, while Figure 21 shows the variation of the basement tensile stress and pile shear with excavation distance. The left side of the vertical dotted line in the Figures 20 and 21 represented the excavation of the left line tunnel, while the right side represented the excavation of the right line tunnel. From Figure 20, it can be found that the successive excavation of double shield tunnels had a significant nonlinear effect on the lateral displacement of the pile along the excavation direction and the subsidence of the building. Building subsidence increases with the increase of shield tunneling distance, and the building subsidence increases from 0.09 mm at the beginning to 7.22 mm at the end of the excavation. When the excavation distance of the left (right) tunnel was less than 50 m, the subsidence of the building increased sharply with the increase of shield tunneling distance. When the excavation distance was greater than 50 m, the subsidence of the building increased slowly with the shield tunneling distance. This phenomenon was similar to the conclusions obtained in reference [31]. Due to the accumulation of subsidence and the secondary disturbance to the soil of the right tunnel excavation, the subsidence of the building caused by the excavation of the right line tunnel was always greater than the subsidence of the building caused by the excavation of the left line tunnel. The lateral displacement of the pile increased from 0.09 mm at the beginning to 3.82 mm during the excavation of the right tunnel. In addition, from Figure 20, it can be found that when the left (right) line excavation distance was less than 50 m, the  
Figure 20: Variations of building subsidence and lateral displacement of pile with excavation distance. lateral displacement of the pile increased sharply with the increase of shield tunneling distance. When the excavation distance was greater than 50 m, the lateral displacement of the pile reduced slowly with the excavation of the shield tunnel. From Figure 21, it can be found that with the construction of shield tunnels, the tensile stress in the basement varied from 7902.7 kPa to 7958.2 kPa, with a variation of 0.70%. The shear force of the pile varied from 111.8 kN to 113.2 kN, with a variation of 1.25%. It can be seen that the effect of the successive excavation of the shield tunnels on the tensile stress of the basement and the shear force of the pile can be ignored. From Figure 22, combined with the variation of the subsidence of the building with the excavation distance, it can be found that the shield tunneling caused uneven subsidence of the building. When the excavation of the shield tunnel started, subsidence would occur in front of the building along the shield excavation direction but not yet behind the building, causing the building to tilt and leading to lateral displacement of the pile. When the shield tunneling reached the rear part of the building, the rear part of the building also gradually started to settle, which made the uneven subsidence of the building balanced. Therefore the tilt of the building gradually reduced, and the lateral displacement of the pile also slowly reduced. In addition, the excavation of the double shield tunnels would result in lateral displacement of the soil around the tunnel. Lateral displacement of the pile would also occur due to the interaction between the piles and the soil.