Experimental test on passive seismic methods for the monitoring of embankments

Earthen embankment are important structures in Alpine regions, their characterization and continuous monitoring is necessary in order to verify their stability and integrity over time. This aspect has such a vital role in these areas, as the economy and social community has a strong dependence on the stability of embankments. Although there are lots of studies conducting with ERT or active seismic monitoring of embankment, there are lack of such studies to continuous monitoring and characterization of earthen embankments particularly in Alpine regions. Henc, the aim of this study is to conduct a continuous monitoring and characterization of an earthen embankment for a short period of time from July 2023 to May 2024 with passive seismic investigation. The selected site is Fourcare embankment located in Aosta Valley northwest of Italy built by Monta rosa company to support water needed for snow production of the Larici ski resort. Passive seismic geophysical method was chosen as it is non-invasive, cost-effective, and allows for continuous data collection. Passive seismic method uses ambient seismic noise without the need to have active source to create artificial wave. In this case, we had the data from four passive seismic monitoring stations at Fourcare embankment along with meteorological data from the nearest meteorological station to the embankment. The method performed Power Spectral Density Analysis verified that the ambient noise falls within the Peterson’s New Noise Model and New High Noise Model. Following that the Ambient Seismic Noise Spectral Analysis was performed which characterized the resonance frequency of the embankment body around 10 Hz which was almost stable over time. Additionally, microseismicity analysis was performed that detect microseismic events with the STA/LTA algorithm. After event detection, classification was done by visual interpretation and two main categories was identified. The first category has the characteristic of low frequency and short time duration which potentially is associated with the propagation of fractures in the embankment structure. And second category has a characteristic of longer frequency around 40 Hz with longer duration which is likely related to water infiltration in shallower layers. Furthermore, the cumulative number of events was shown and analyse its response to temperature which shows that there is when temperature drops around October the number of microseismic events increased. Finally, the scatter plot of frequency of events was done. The peak frequency of events reveals that the microseismic events are mainly scattered around two distinct frequencies. Moreover, it shows that the combination of temperature drop, and precipitation can aggregate the peak of frequencies around these two frequencies. This study shows that there can be done further studies to continuous monitoring of embankments even for longer periods of time.