## 3 Measured Analysis of Stratum Deformation
### Analysis of Vertical Displacement of Stratum  
Figure 7 is the time history curve of the surface vertical displacement of monitoring section A. The horizontal axis represents the distance between the cutter head and the monitoring section. A positive value indicates that the cutter has passed through the section, whereas a negative value indicates that the cutter has not reached the section. The vertical axis represents the vertical displacement of the ground surface. A positive value is the ground heave, whereas a negative value is the ground settlement. The surface vertical displacement experienced the following four stages during shield tunneling: (1) When the cutter moves gradually close to section A, the vertical displacement of the surface gradually rises (0-3.2 mm) under the joint action of thrust force and chamber earth pressure. When the cutter reaches the section, the heave is close to the maximum. (2) When the cutter passes through section A, the soil above the shield machine is no longer affected by thrust force and chamber earth pressure. Due to the combined influence of shield posture, shield tail void, and grouting pressure, settlement occurs in the monitoring section. With the excessive grouting pressure, the section soil heaved again. The grouting pressure not only affects the vertical displacement of the soil behind the shield tail but also penetrates into the soil in front of the shield tail, resulting in a change in the vertical displacement of the soil. (3) When the shield tail passes section A, the existence of the gap at the shield tail will theoretically produce soil settlement. However, due to the influence of grouting, and a large grouting pressure (0.249 MPa) is applied at this time, the soil continues to rise by about 0.1 mm compared with the previous stage. (4) When the shield tail is far away from section A, the soil deformation of the section is no longer within the radiation range of the grouting effect, and with the dissipation of pore water pressure, the soil still has a consolidation settlement of about 0.6 mm. Figure 8 shows the vertical displacement of stratum soil in monitoring section A. The field monitoring results show that the development law of ground deformation at 2 m, 4 m, 6 m, and 8 m below the surface with the advance of the shield is basically consistent with the ground deformation, and generally experiences the four development stages of  
Figure 7: Development of surface settlement during tunneling in Section A.  
time history change described above. The stratum with large deformation is 6 m below the surface (located in the middle and lower part of the silt-silty clay layer) and 8 m below the surface (at the bottom of the silt-silty clay layer). In Figure 8a, the cumulative maximum heat at 6 m below the surface is 4.21 mm, and the cumulative maximum heat at 8 m below the surface is 4.47 mm. In Figure 8b, the cumulative maximum heat at 6 m below the surface is 3.81 mm, and the cumulative maximum heat at 8 m below the surface is 4.09 mm. In Figure 8c, the cumulative maximum heat at 6 m below the surface is 3.29 mm, and the cumulative maximum heat at 8 m below the surface is 3.64 mm. In summary, major increments in heavy deformation values occur in the stage before the shield cutter reaches the monitoring section. Due to the extrusion disturbance of shield tunneling on the front soil, the heavy deformation of soil increases. When the shield crosses the monitoring section, the shield tail grouting has a great impact on the soil deformation value of the section. Under the joint action of grouting pressure and grouting volume, the shield tail passing the section reaches the maximum value. Figure 9 is the time history curve of the surface vertical displacement of monitoring section B. As shown in Figure 9, the surface vertical displacement experiences the following five stages during tunneling: (1) When the cutter head is far away from section B, the vertical displacement of the ground surface hardly changes.