## 3 Measured Analysis of Stratum Deformation
### Analysis of Vertical Displacement of Stratum
(2) When the cutter approaches section B, under the joint action of thrust force and chamber earth pressure, the soil in front of the shield is extruded and deformed. The surface begins to rise, and the amount of heave increases gradually (about 0-1.5 mm). (3) When the cutter passes through section B, the soil layer above the shield machine is no longer affected by thrust force and the chamber earth pressure. Due to the influence of shield posture and the existence of shield tail clearance, the monitoring section has a settlement. As the shield moves forward, the section soil layer  
Figure 8: Vertical displacement of stratum soil in Section A: (**a**) SIIP-S-1; (**b**) SIIP-S-2; and (**c**) SIIP-S-3. rises again due to the excessive grouting pressure at the tail of the shield. This phenomenon shows that 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 in front. (4) When the shield tail is about to pass section B, and due to the existence of a gap at the shield tail and the fact that the shield crossing layer is a round gravel layer, the porosity is large. After the gap is generated, the soil above falls rapidly and causes a large settlement (about 1-1.5 mm). (5) After the shield tail passes through section B, the consolidation settlement (about 0.7 mm) of the surface soil occurs with the gradual dissipation of pore water pressure. Figure 10 shows the vertical displacement of soil mass on section B. The field monitoring results show that the development law of stratum deformation at 2 m, 4 m, 6 m, 8 m, and 10 m below the surface with the advance of the shield is basically consistent with the surface deformation, and large stratum deformation occurs at 6 m below the surface (located in the middle and lower part of the silt-silty clay layer) and 10 m below the surface (the interface between round gravel layer and silty clay layer, closest to the top of the tunnel). In Figure 10a, the cumulative maximum heave at 6 m below the surface is 1.71 mm and the cumulative maximum settlement is 7.37 mm; the cumulative maximum heave at 10 m below the surface is 2.78 mm and the cumulative maximum settlement is 6.9 mm. In Figure 10b, the cumulative maximum heave at 6 m below the surface is 1.03 mm and the cumulative maximum settlement is 5.51 mm. The cumulative maximum heave at 10 m below the surface is 1.44 mm and the cumulative maximum settlement is 5.34 mm. In Figure 10c, the cumulative maximum heave at 6 m below the surface is 2.57 mm and the cumulative maximum settlement is 6.43 mm. The cumulative maximum heave at 10 m below the surface is 3.85 mm and the cumulative maximum settlement is 6.23 mm. In summary, the maximum heave deformation occurs at the stage before the shield cutter reaches the monitoring section. Due to the extrusion disturbance of shield tunneling on the soil in front, the heave deformation of the soil increases. The maximum settlement is at a long distance after the shield tail passes through the monitoring section. Due to the shield tail passing section, the existence of a gap at the shield tail will produce a corresponding settlement. In addition, the dissipation of excess pore water pressure after crossing leads to consolidation settlement of the soil, which further increases the settlement of the soil. Figure 9: Time history curve of surface vertical displacement of section B.