Acoustic Methods to Detect Anomalies in an Embankment Dam – A Comparison With Other Geophysical Methods

In Sweden, the majority of the large dams were constructed in the 1950s to the 1970s. With an ever-ageing population of dams, it has become increasingly important to be able to detect and locate anomalies. During 2020, increased seepage was detected in the automated monitoring system in a roughly 1600m long embankment dam. The dam and the downstream area were inspected and data from the monitoring equipment were evaluated. To investigate the conditions, the drainage pipes were filmed from the inside. Also, the seepage path was traced via temperature measurements in an optical cable embedded under the dam toe. To identify the seepage path, in a first step the dam was investigated with ground-penetrating radar. Further investigation was needed to get more information. Since strong winter conditions prevented several investigation methods, it was decided to try passive acoustic imaging (Ambient Noise Interferometry), using an optical fiber on the dam crest (Distributed Acoustic Sensing). This is a recently introduced method and it has only been tried on a handful of dams. Initial findings have been positive, and this case offered a possibility to compare the acoustic data output with the radar image, temperature, and resistivity measurements.