# Investigation into the Construction Response of Tunnels through Fault: Model Test
## 4 Results' Analyses  
### Analyses of Surrounding Rock Pressure  
During the model tunnel excavation process, the surrounding rock pressure was measured at each step in the SL area, as shown in the line diagram presented in Figure 10. The tunnel was excavated using the CD method with three different fault dip angles: 45\({}^{\circ}\), 60\({}^{\circ}\), and 75\({}^{\circ}\). Analysis of the collected data revealed that the surrounding rock pressure increased as the fault dip angle increased. Specifically, the surrounding rock pressure was highest for the 75\({}^{\circ}\) fault dip angle, followed by the 60\({}^{\circ}\) fault dip angle, and then the 45\({}^{\circ}\) fault dip angle.  
Point 3 at the circumferential 1.5 D measuring line displayed a stable variation range in the measured pressure. The most significant increase occurred at the left-side wall (SL1, Point 3) under the 60\({}^{\circ}\) fault dip angle condition. The initial surrounding rock pressure was 6.65 kPa and the final stable surrounding rock pressure was 7.02 kPa, representing a growth factor of 1.055 times. Additionally, the surrounding rock pressure at the vault exhibited a slight decrease, with the most significant drop occurring at the vault (SL3, Point 3) under the 45\({}^{\circ}\) fault dip angle condition. The initial surrounding rock pressure was 6.188 kPa and the final surrounding rock pressure was 6.931 kPa, representing a reduction factor of 0.875 times.  
Figure 10: _Cont._The measured surrounding rock pressure of Point 2 at the circumferential 1.0 D measuring line has a relatively small range of variation. The position with the highest increase in pressure is the right-side wall (SL5, Point 2) under the condition of 45\({}^{\circ}\) fault dip angle. The initial surrounding rock pressure is 6.188 kPa and the final stable surrounding rock pressure is 6.931 kPa, resulting in an increase factor of 1.12 times. Conversely, under the 75\({}^{\circ}\) fault dip angle, the most significant decrease in pressure is observed at the vault (SL3, Point 2). The initial surrounding rock pressure is 8.19 kPa and the final stable surrounding rock pressure is 7.26 kPa, resulting in a reduction factor of 0.887 times.  
The measured surrounding rock pressure at the circumferential 0.5 D (0.5 times the tunnel diameter) measuring line exhibits significant changes. The left spandrel (SL2, Point 1) under the 45\({}^{\circ}\) fault dip angle has the highest increase in surrounding rock pressure. The initial surrounding rock pressure is 11.6 kPa and the final surrounding rock pressure is 37.63 kPa, resulting in an increase factor of 3.24 times. In contrast, the vault (SL3, Point 1) under the 75\({}^{\circ}\) fault dip angle has the greatest decrease in surrounding rock pressure. The initial surrounding rock pressure is 11.32 kPa and the final stable surrounding rock pressure is 7.09 kPa. The reduction factor is 0.63 times.  
Moreover, the surrounding rock pressure at the spandrel (SL2, SL4) exhibits significant changes at the 0.5 D measuring line, with the pressure reaching 3.11-3.24 times the initial pressure. However, at the 1.0 D measuring line and 1.5 D measuring line, the surrounding rock pressure is generally stable, with a variation range of 0.98-1.02 times the initial pressure.  
Based on the analysis presented, several conclusions can be drawn:  
1. A steeper fault dip angle is associated with greater radial surrounding rock pressure.
2. Following tunnel excavation, the surrounding rock pressure at the vault decreases, while pressure at other locations increases.
3. The radial pressure at the vault experiences a significant reduction, with the influence depth of the surrounding rock pressure reduction extending up to 1.5 D.
4. The pressure at the spandrel displays a higher amplitude compared with that at the vault, with the influence depth limited to 0.5 D.
5. The radial pressure at the arch waist exhibits only slight changes, and the influence depth is less than 0.5 D.