# Analysis of Shield Tunnels Undercrossing an Existing Building and Tunnel Reinforcement Measures
## 6 Effect of Grouting Pressure on Mechanical Behaviors of Soil, Segment, and Building
### Effect of Grouting Pressure on Internal Forces of Segment  
Similar to Section 5.2.1, the ring segment below the center of the building was considered the analysis objective. The numbers at different circumferential positions of the segment were also found in Figure 17. Figures 25 and 26 show the variation curves of the bending moment and circumferential axial force of segments with grouting pressure, respectively. From Figure 25, it can be found that for the same segment, no matter the left tunnel or the right tunnel, the variety rule of the bending moment was the same with different grouting pressures. The maximum positive bending moment of the segments still occurred near the tunnel arch crown and arch bottom, and the maximum negative bending moment occurred near the arch waist. For the segment of the left line tunnel, when the grouting pressure was 150 kPa, the bending moment of the segment was the largest, and its maximum value was 89.73 kN\(\cdot\)m. When the grouting pressure was 550 kPa, the maximum bending moment of the segment was 61.24 kN\(\cdot\)m, which was 31.75% less than the maximum bending moment of the segment for the grouting pressure of 150 kPa. For the segment of the right line tunnel, when the grouting pressure was 150 kPa, the bending moment of the segment  
Figure 26: Relationship between axial force of segments and grouting pressure: (**a**) segment of left tunnel (first tunnel); (**b**) segment of right tunnel (second tunnel). Figure 25: Relationship between bending moment of segments and grouting pressure: (**a**) segment of left tunnel (first tunnel); (**b**) segment of right tunnel (second tunnel). was the largest, and its maximum value was 72.65 kN\(\cdot\)m. While the grouting pressure was 550 kPa, the maximum bending moment of the segment was 57.33 kN\(\cdot\)m, which was 21.09% less than the maximum bending moment of the segment for the grouting pressure of 150 kPa. From Figure 26, it can be found that for the same segment, no matter which tunnel, the variety rule of axial force was the same with different grouting pressures. The axial force everywhere in the segment was still pressure. For the left line tunnel, when the grouting pressure increased, the axial force of the segment also increased. When the grouting pressure was 50 kPa, the maximum axial force of the segment was 810.56 kN; when the grouting pressure was 550 kPa, the maximum axial force of the segment was 1782.71 kN, which was 119.34% higher than that for the grouting pressure of 50 kPa. From Figure 26, it can be found that for the right line tunnel, when the grouting pressures were 50 kPa, 150 kPa, and 250 kPa, the axial forces of the segment directly below the right line tunnel building were basically the same, and the maximum value was 1178.94 kN, while the grouting pressures were within the range of 250-550 kPa, the axial force of the segment of the right line tunnel increased with the increase of the grouting pressure. While the grouting pressure was 550 kPa, the maximum axial force of the segment was 1768.52 kN, which was 50.01% higher than that for the grouting pressures of 50 kPa, 150 kPa, and 250 kPa. For researching the effect of grouting pressure on the extremum of internal force of segment of double shield tunnels, the maximum longitudinal and transverse stresses of all segments of double shield tunnels under each grouting pressure value were extracted. Figure 27 shows the curve of its relationship with grouting pressure. From Figure 27, it can be found that when the grouting pressures were in the range of 50 kPa-250 kPa, the maximum longitudinal and transverse stresses reduced linearly with the increase of grouting pressure. When the grouting pressures were in the range of 250 kPa-550 kPa, the maximum longitudinal and transverse stresses increased linearly with the increase of grouting pressure.