In this article, we suggest a new type of seismic source for surveying both structure state and foundation soil conditions regardless of the level of seismic noise. In our opinion, powerful industrial equipment can be treated as seismic sources. We describe the results of a survey conducted on the Song Tranh-2 hydropower dam located in Central Vietnam. After a М = 4.7 earthquake, the dam visual inspection revealed zones of the excessive durability loss: cracks and areas with an elevated infiltration of water into the dam galleries. Powerful industrial equipment generates continuous quasi-harmonic mechanical oscillations (seismic waves) that travel through layers of rocks. These seismic oscillations are recorded by receivers in different measurement points such as the dam body, abutments, and the foundation soils. Anomalous amplitudes of these oscillations indicate the presence of weakened zones in the structure or in foundation soil. We coupled passive and active seismic methods to more precisely find such zones. In this case, active seismic methods allowed us to investigate dam abutment zones, and passive seismic methods were used to localize weakened zones in the dam-foundation soil system. We assumed that the joint contribution of two factors was the cause of the dam weakening. One of them was caused by increased water infiltration through the rock mass and its contact zones, and the other was reservoir-induced seismicity contributing to the deterioration of the foundation soils, which was possibly the reason for a shift in the dam in the contact zone with the rock mass foundation. It is necessary to perform computer modelling, which was not included in our research. The developed method can be used for the safety control of the hydropower station dams.
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