# Model Test on Effect of Ground Fissure on the Behavior of Oblique Two-Section Subway Tunnel
## 3 Results and Discussion
### Dynamic Response of Earth Pressure  
Figures 16-18 show the additional earth pressure at different depths under the 10 Hz excitation. Here, the additional earth pressure implies the difference in earth pressure before and after the application of the excitation load. Positive earth pressure is observed in all the survey lines when the ground fissure is inactive, and the earth pressure increases with the embedded depth. According to the test results, the main reasons for such a phenomenon can be deduced as: (1) the static earth pressure increases with the buried depth and (2) the distance of the three layers (from bottom to top) to the vibration exciter increases in sequence, and, thus, the impact of vibration decreases in sequence. Furthermore, in the longitudinal direction of the tunnel, the additional earth pressure on the same side as the vibration exciter is greater than that on the other side as the earth pressure significantly decreases when crossing the ground fissure, while the maximum additional earth pressure in the vertical direction is identified near the tunnel axis. Figure 14: Acceleration time series under the combined impact of hanging wall descending (1 cm) and 10 Hz excitation: (**a**) vibration exciter at 60 cm; (**b**) vibration exciter at 100 cm. Figure 15: Peak acceleration curves under the combined impact of hanging wall descending (1 cm) and 10 Hz excitation: (**a**) vibration exciter at 60 cm; (**b**) vibration exciter at 100 cm. Figure 19-21 depict the additional earth pressure at different depths due to the descending of the ground fissure hanging wall (1 cm). The additional earth pressure at the height of 15 cm (10 cm below the tunnel) in the hanging wall is basically 0 because of the generated voids between the tunnel and the underlying soil. The additional earth pressure  
Figure 16: Additional earth pressure at 15 cm height under the scenario of inactive ground fissure: (**a**) vibration exciter at 60 cm; (**b**) vibration exciter at 100 cm. Figure 17: Additional earth pressure at 50 cm height under the scenario of inactive ground fissure: (**a**) vibration exciter at 60 cm; (**b**) vibration exciter at 100 cm. Figure 18: Additional earth pressure at 85 cm height under the scenario of inactive ground fissure: (**a**) vibration exciter at 60 cm; (**b**) vibration exciter at 100 cm. in the footwall increases compared with the condition of the inactive ground fissure, and the largest additional earth pressure is identified at the axis of the tunnel. This phenomenon is caused by the compaction between the tunnel (in the footwall) and the underlying soil under the action of vibration. Furthermore, when the working vibration exciter varies from 60 cm (in the footwall) to 100 cm (in the hanging wall), the additional earth pressure in the footwall is reduced because of the larger distance from the excitation point. The test results of the two survey lines with a height of 50 cm show a huge difference in earth pressure between the hanging wall and footwall. Negative values are observed in the hanging wall, indicating the slight decreasing earth pressure caused by vibration in this region. Additionally, the additional earth pressure in the footwall shows a larger value, yet it decreases when the vibration exciter moves from the footwall to the hanging wall. Figure 19: Additional earth pressure at 15 cm height under the scenario of hanging wall descending (1 cm): (**a**) vibration exciter at 60 cm; (**b**) vibration exciter at 100 cm. Figure 20: Additional earth pressure at 50 cm height under the scenario of hanging wall descending (1 cm): (**a**) vibration exciter at 60 cm; (**b**) vibration exciter at 100 cm. The test results of additional earth pressure at 85 cm (\(\sim\)12 cm above the tunnel) indicate a quite different variation from the upper two layers. The measured additional earth pressure at survey line P3-2 shows a positive value in the hanging wall while showing a negative value in the footwall.