Ambient seismic noise imaging of a tailings dam internal structure

Abstract

Several tailings dam failures have been reported over the past few decades, raising questions about the stability of these structures. Over the past 30 years, there have been more severe failures of tailings dams, which have resulted in damage to the environment, fatalities and severe socio-economic issues. It is often impossible to predict when tailings dams could fail, so there is an urgent need to develop cost-effective methods for monitoring their stability and preventing such catastrophic events. Recent advancements in techniques related to ambient seismic noise have the potential to introduce new approaches to subsurface imaging and monitoring. In this study, we investigated the potential of using ambient seismic noise to monitor the interior wall of a tailings dam. We used 20 3C short-period geophones to record ambient noise over 3 days continuously. We set up the geophones at the Harmony Gold Mine tailings dam in Welkom, South Africa, along a survey profile approximately 100 m long. Seismic interferometry was used from the recorded data to retrieve empirical Green’s functions. We computed the dispersion curves’ inversion to determine the dam wall’s shear wave velocity at different depths. The calculated shear wave velocity cross-sections revealed a region of reduced velocity within the dam wall, situated between 2 m and 10 m beneath the surface. This zone of low velocity can be a sign of water-saturated material or other subsurface anomalies, which might jeopardise the dam’s structure. Significance: Tailings dams have a long history of ruptures and collapse. The results from this study indicate that passive seismic interferometry can be a cost-effective tool for imaging and identifying minor changes within the interior of the tailings dam wall. This technique could prove valuable in detecting potential instabilities before they reach a critical stage. This can allow for early intervention and remedial measures, such as reinforcing the dam wall or adjusting the water levels in the tailings dam.

Keywords

• tailings
• seismic interferometry
• ambient seismic noise
• Green’s function
• imaging