## 3 Ambient Vibration Analysis
### Research on Pipeline Vibration  
Two measurement points, P5 and P6, were set directly above the diversion pipeline. Previous studies researched the ambient vibration in the ground, and the ground vibration was generated by the vibration of the diversion pipeline via the mountains. Therefore, the extent to which the vibration of the diversion pipeline diminishes after the vibration reaches the ground is significant to study. \begin{table}
\begin{tabular}{c c} \hline \hline
**Conditions** & **Power (MW)** \\ \hline Unit 4\# under pumping conditions & \(-344\) \\ Units 1\# and 4\# under pumping conditions & \(-651\) \\ Units 1\#, 3\#, and 4\# under pumping conditions & \(-980\) \\ Units 1\#, 2\#, 4\#, and 5\# under pumping conditions & \(-1384\) \\ Units 1\#, 2\#, 3\#, 4\#, and 5\# under pumping conditions & \(-1687\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Pumping working conditions. Figure 10: The variation in the root–mean of vibration with power under pumping conditions. Figure 9: Variation in the root–mean of vibration with power under power generation conditions. As depicted in Figure 11, a small section of exposed steel lining in the latter half of the horizontal flat tunnel section of the diversion pipeline of the PSPS facilitated maintenance. This section could be accessed through the construction branch of 3#. Measuring points P5 and P6 within the horizontal flat tunnel were directly connected to diversion pipelines 2# and 3#, experiencing negligible external interference. Additionally, units 1# and 2# shared the same diversion pipeline of 1#, units 3# and 4# shared another diversion pipeline of 2#, and units 5# and 6# shared another diversion pipeline of 3#. The collected data during testing originated solely from vibrations generated by these diversion pipelines while running the units. This section researches the law of vibration acceleration in the diversion pipeline with the increase in the number of units running under different conditions. The working conditions are shown in Table 7.  
As shown in Figure 12, the amplitudes of measuring points P5 and P6 were larger than the others. Under sectional conditions, the amplitude reached 35, indicating that the energy was greatly weakened from the diversion pipeline to the ground compared with the ground vibration. Compared with the other spectrum maps of the working conditions, the energy was predominantly concentrated around 70 Hz and 120 Hz in the majority of working conditions. Based on Figure 13, measurement point P6 in units 1# and 4# generated a root-mean of vibration of approximately 0.68 cm/s\({}^{2}\) while running the diversion pipeline of 2# under power generation conditions. The diversion pipeline of 3# was not running at that time. Based on this phenomenon, mutual interference occurred while running the adjacent pipelines. Moreover, the root-mean of vibration increased with the increasing number of units in operation, with a maximum value of 76 cm/s\({}^{2}\). The presence of mountains significantly attenuated the magnitude of vibrations. The ground vibration was caused by the vibration of the diversion pipeline. Figure 11: Position diagram of measuring points in the horizontal flat tunnel. \begin{table}
\begin{tabular}{l c} \hline \hline
**Conditions** & **Power (MW)** \\ \hline Units 1\# and 4\# under power generation conditions & 350 \\ Units 1\#, 4\#, and 5\# under power generation conditions & 1050 \\ Units 1\#, 3\#, 4\#, and 5\# under pumping conditions & \(-\)1380 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Working conditions. Figure 12: The spectrum maps of units 1# and 4# and units 1#, 4#, and 5# under power generation conditions, and units 1#, 3#, 4#, and 5# in pumping conditions.