Seepage contributed by groundwater can pose a major threat to the safe operation of tailings dams, with the potential to compromise stability of containment embankments if left undetected and unmanaged. Visual inspection and intrusive geotechnical investigation are commonly used to characterise such problems, however often prove unreliable in identifying the source and extent of seepage flow paths, and any interaction with groundwater. Early identification is therefore critical to assessing the integrity of dam structures, with the use of geophysical surveys proving effective in achieving this outcome.
Geophysical techniques were utilised at two mine sites in Queensland to investigate areas of known seepage expression at tailings dam embankments. The purpose of the work was to compliment desk study analysis to gain an understanding of the seepage mechanism, which would in turn inform design of suitable groundwater management systems. Electrical resistivity (ER) and time domain electromagnetic (TDEM) methods were selected due to ease of use and rapid turnaround time for results. Both techniques produce a depth electrical profile of the conductivity of soil/rock for geotechnical interpretation, and contrasting groundwater conductivity to signify preferred seepage pathways.
At the case study sites, the key objective was to assess the likely pathways of seepage, either through the embankment or via more permeable zones located within underlying aquifers. These works demonstrated the benefit of using geophysical methods to target known seepage issues, and assisted in the siting and design of effective groundwater management systems for maintaining embankment integrity. It is concluded that for assessment of the post-construction performance of tailings dams, regular geophysical surveys could act as an early warning of any developing groundwater issues.