Earthen dam monitoring using passive seismic: a forward modeling study

Abstract

Internal erosion caused by infiltration and piping is the main cause of earthen dams’ failures. Traditional methods of inspection are not representative and are unable to cover the entire structure. The seismic interferometry emerges as an alternative for continuous monitoring earthen dams from the detection of variations in seismic velocities caused by water saturation. The objective of this study is the geophysical investigation of the Paranoá’s dam (Brasília, DF, Brazil) in hypothetical infiltration scenarios. To obtain a geological model that represents the expected structure, we performed an acquisition with active sources in the region and applied inversion techniques to retrieve the seismic velocities. We simulated acquisitions in a simple geological model of two horizontal layers for better understanding the behavior of the retrieved seismograms. The results show that more recording time and a wide receiver coverage improves the signal-to-noise ratio. We simulated a layer saturation by varying the velocities and noticed that the method was able to detect such variations. We noticed alterations in the reflection hyperbola asymptotes and in the first arrival time through the seismograms. The method also verified velocity changes in a more complex geological model. Our results suggest that the traffic energy is sufficient to image the dam’s structure, even not satisfying the theoretical diffuse wave field condition. Furthermore, we implemented a technique to monitor velocity variations using the semblance calculation. The method detected variations in the structure Vp in the order of 10%.