## 4 Vibration Data Analysis
### Peak Acceleration Analysis  
In adjacent two-way tunnels, a common issue arises: there is typically a distance be-tween the two tunnels. In the underground section of the Taizhou Municipal Railway, this distance is nearly 30 m, differing from the usual scenario where adjacent surface tracks are nearby. Consequently, this discrepancy inevitably affects the vibration propagation patterns of train operation. To explore how the interaction between tunnels affects the propagation of vibrations, we will analyze the attenuation patterns of the vibration acceleration caused by train operation at different measurement points. In Figure 8, in the X direction, the attenuation amplitude from P3 to P4 is considerably smaller than that observed from P2 to P3 and P4 to P5. Similarly, in the Y direction, the attenuation amplitude from point P2 to point P3 is notably smaller than from point P1 to point P2 and from point P4 to point P3. The attenuation amplitude from P2 to measuring point P1 in the Z direction is smaller than that from measuring point P2 to measuring point P3. This phenomenon occurs because the presence of adjacent tunnels mitigates energy dissipation during vibration propagation. Additionally, the acceleration in each direction exhibits a decreasing trend as the distance from the tunnel centerline increases, aligning with the research findings of [PERSON] et al. [32] and [PERSON] et al. [33]. Figure 7: Maximum displacement diagram of each measuring point. Figure 8 shows the peak accelerations in the Z and X directions at measuring point P2. In contrast, the minimum acceleration was recorded at measuring point P6, which is the farthest from the centerline of the tunnel traversed by the vehicle. Furthermore, the peak acceleration in the Y direction was recorded at measuring point P1, while the minimum acceleration was observed at measuring point P2, situated above the adjacent tunnel. Comparing the displacement map with the peak acceleration map, it is evident that the minimum peak acceleration and maximum displacement in the X direction occurred at measuring point P6. Similarly, the maximum peak value and displacement in the Y direction were observed at measuring point P1. In contrast, the minimum displacement in the upward Z direction and the maximum peak acceleration occurred at measuring point P2. These observations suggest a correlation between displacement and peak acceleration across the data image. The distribution of displacement and acceleration is not only correlated in the time domain, but is also closely related to spatial location. By comparing data from the measurement points, it is observed that the peak values of displacement and acceleration in the X, Y, and Z directions were concentrated at different measurement points, indicating that the vibration intensity and directionality were strongly linked to each specific point. The analysis of the relationship between displacement and acceleration can inform the optimization of vibration isolation design. For example, at measurement points where peak acceleration and displacement are higher, appropriate isolation pile spacing, materials, or structural designs can be implemented to effectively mitigate vibration propagation and reduce its impact on building structures. High acceleration levels often result in strong vibration sensations, which can negatively affect the living comfort of residents, particularly in residential areas. By analyzing the displacement and acceleration at various measurement points, it is possible to predict the impact of vibrations on nearby residential areas and implement necessary mitigation measures. Comparing the vibration acceleration level data with the peak acceleration data, it was observed that the vibration acceleration level at measuring point P6 in the 6.3 Hz-25 Hz frequency band coincided with the minimum value in the peak acceleration data. Additionally, the locations where the maximum peak acceleration in the Z directions occurred align with the positions of the maximum vibration acceleration level measurements.