15:30 〜 17:00
[HDS05-P04] The variation of seismic frequency during impounding and the seismic signal hysteresis caused by the movement of the riverbed load
キーワード：dam breach, seismic signal, frequency, flood, hysteresis loop
The seismic signals and water level data measured from a large-scale dam breach test were used to analyze the seismic frequency variation of the dam during impounding. Also, the characteristics of the seismic signal generated by flood and riverbed load movement during dam breach were discussed. The Hilbert-Huang transform (HHT), Fourier transform (FT), and Short-time Fourier transform (STFT) were used to analyze the seismic signals. The results show that the seismic frequency of the dam became lower and lower during the impounding. The decrease in the seismic frequency of the dam may be caused by the restriction of water pressure or due to water infiltration into the dam. After water infiltration, the shear strength and stability of the dam should decrease. Therefore, the decrease in the seismic frequency of the dam can be regarded as an early warning that the impounding water level is rising. We also found that there is a clockwise hysteresis loop in the plot of the seismic power spectral density (PSD) versus flood level; i.e., there are high and low PSD values at the same water levels. This is because the bedload was transported by the rising flood, resulting in higher seismic energy; when the flood recedes, it is gradually unable to move the bedload thereby the seismic energy becomes smaller. This study also confirmed that the seismic energy of the dam body is the strongest in the direction parallel to the water flow, which also means that we may apply the outcome to identify the direction of water erosion.