Monitoring of tailings dam stability using cross-spectral-density-based passive HVSR measurement

There is an increasing need for effective tools to assess the structural condition and damage evolution of tailings dams, given their high risk of catastrophic failure and associated secondary disasters. In this study, we present a novel cross-spectral-density-based horizontal-to-vertical spectral ratio (CSD-HVSR) method that enables monitoring of the resonant frequency of tailings dams. Taking advantage of the full cross-terms of three-component passive ambient seismic recordings, this method offers improved stability and reliability over conventional HVSR techniques. We apply the method to examine seismic data collected over 1 year at the XiaoDongGou tailings dam in Chengde, China. The resulting daily fundamental resonant frequency exhibits clear, reversible fluctuations in response to external weather conditions, revealing dynamic changes in water and stress states within the tailings dam. We attribute these fluctuations primarily to variations in the seismic velocity of the top tailings layers and/or perturbations in the phreatic surface, which links resonant frequency behaviors to key metrics of tailings dam stability. These results highlight the strong potential of the CSD-HVSR method for future structural health monitoring.