Imaging and monitoring tailings dam walls with ambient seismic noise

Abstract

This paper was originally published in the Proceedings of the 9th International Symposium on Rockbursts and Seismicity in Mines (RaSiM9). Acknowledgement is given to the University of Chile for their permission to republish this paper. Tailings dams are massive structures that are designed to contain the waste slurry remaining after processing ore at open pit and underground mines. These structures fail far more regularly than normal water storage dams, and in recent years catastrophic tailings dam failures have occurred, causing significant damage to the environment and even loss of life. To mitigate these catastrophic events in the future, there is an urgent need to develop costeffective methods to monitor the structural stability of these constructions over time. The lack of current costeffective subsurface imaging and monitoring methods prompted us to investigate whether ambient seismic noise can be used to image and detect internal changes in a tailings dam wall during a period of heavy rainfall. We recorded three weeks of continuous seismic data with 10 short-period geophones at a tailings dam in Tasmania, Australia. Seismic interferometry was used on ambient noise to create virtual seismic sources. With these virtual source signals, small changes in seismic velocity were measured daily and compared to rainfall, seepage flow rates and fluid pore pressure. The observed velocity changes were driven by fluid saturation, groundwater level, increased loading from increased dam water level and a sudden increase in fluid pore pressure in a section of the dam wall. A further experiment was performed at a tailings dam in South Africa, where ambient noise surface wave tomography was used to image an area where seepage was identified. The results suggest that these relatively inexpensive methods can be used to monitor and locate small changes in the interior of tailings dam walls, providing a valuable tool for remotely monitoring the structural stability of tailings dam walls over time.