## 3 Results and Analysis
### Evolution Law of Surface Subspace  
#### 3.1.1 Field Monitoring Results  
Figure 5 is the longitudinal settlement curve of holes 1 # through 3 # monitoring points on the surface. The longitudinal settlement curve of ground surface in the process of shield tunneling can be divided into three stages: shield approaching (\(-\)30-0 m), shield crossing (0\(-\)6 m) and shield tail falling out (6\(-\)30 m). Among them, the shield approaching stage can also be divided into initial deformation stage (\(-\)30\(-\)\(-\)6 m) and micro deformation stage (\(-\)6\(-\)0 m). The former curve changes gently, indicating that the shield tunneling disturbance has little effect on the surface settlement of the monitoring point. In the latter stage, the surface settlement deformation rate gradually increases but the deformation value is relatively small, and the maximum settlement of the approaching stage is reached when the cutterhead reaches the monitoring section. In addition, the surface subsidence increases rapidly from the shield crossing to the shield tail stripping stage, which is intuitively reflected in the increase of the slope of the curve. When the shield tail is separated from the cutterhead and passes through the monitoring section of 18 m (3D), the ground settlement reaches \(-\)11.59 mm, \(-\)12.04 mm and \(-\)11.19 mm, respectively. At this time, the settlement accounts for more than 2/3 of the total settlement, which is the main deformation zone disturbed by shield tunneling, and the subsequent displacement gradually stabilizes. Based  
Figure 4: Numerical simulation monitoring point layout diagram.  
on the above analysis, it can be seen that the influence range of shield tunneling disturbance is about 3.0 times the hole diameter in front of the tunnel face to 1.0 times the hole diameter behind the tunnel face.  
Figure 6 is the lateral displacement curve of the surface site monitoring point. It can be seen that when the shield cutter has just reached the monitoring section, the maximum surface settlement is \(-1.69\) mm, the surface deformation is not obvious, there is no obvious settlement trough; when the cutterhead is 6 m away from the monitoring section, the maximum settlement value of the surface increases sharply, the maximum settlement value reaches \(-10.10\) mm, and the settlement trough begins to appear gradually. When the shield cutterhead is 12 m away from the monitoring section, the lateral settlement of the surface tends to be stable, and the maximum settlement value reaches \(-11.59\) mm. At this time, the shield cutterhead is about twice the outer diameter of the shield from the monitoring section, and the settlement trough is basically formed. In the stage of shield tail disengaging, the increasing amplitude of surface transverse settlement decreases gradually. When the shield cutterhead is 30m away from the monitoring section, the settlement value of transverse monitoring section reaches the peak value \(-12.77\) mm. In addition, in the stage of shield crossing and shield tail disengagement, the surface settlement above the tunnel vault (hole 2 # surface monitoring point) is always the largest. The surface settlement is the most obvious in the range of 1 time the outer diameter of the shield (\(-6\)-\(6\) m) on both sides of the tunnel center, and the influence range of the whole excavation disturbance is 1.5 times the outer diameter of the shield on both sides of the tunnel center (\(-9\)-\(9\) m).  
Figure 5: Variation of ground surface longitudinal settlement with the advancement of tunnel.