Tailings storage facilities (TSFs) are an essential infrastructure of mineral processing, but they represent a significant physical, chemical and biological hazard and must, therefore, be strictly and responsibly sited, managed and closed. Tailings can, for example, be dispersed by many processes (such as sinkholes, earthquakes, intense rainfall and flood events, and wind), substandard design and construction, and seepage. The stability and behaviour of TSFs needs to be continuously monitored and one highly effective way of doing this is through satellite Earth observation (EO). The EO industry is witnessing a technological revolution. Large and long-lifespan satellite sensors that have been the staple of national space agencies and commercial satellite manufacturers are now being complemented by constellations of low-cost, short-lifespan cube sats by companies with the ambition to image the whole earth daily. Satellites with synthetic aperture radar (SAR) sensors are also collecting high volumes of data, with the added benefit of being able to do so day or night and in different weather conditions. The range of data options and capabilities these provide open opportunities for novel data analysis techniques for TSFs. One of these is satellite InSAR (interferometric SAR; a technique used to map millimetric-precision changes in ground height over time), which is already used by mining companies to reduce risk in and of their operations. From monitoring the stability of TSFs, through to assessments of impacts of natural hazards, InSAR allows rapid and accurate targeting of high-risk areas and structures to identify those that require subsequent investigation through ground-based methods. To demonstrate the application of EO data and InSAR in identifying pre- and post-failure mine activities and TSF deformation, the authors will present a case study across Cadia mine, New South Wales, Australia, which had a localised TSF failure on 9 March 2018. The InSAR results presented show that low-magnitude subsidence signals were observed across the TSF dam during the year preceding the collapse. In January 2018 a notable change in behaviour was observed, with a concentrated area of subsidence focused on the region which initially failed on 9 March 2018. Furthermore, post-collapse InSAR measurements show an increased rate of subsidence for regions either side of the failure zone. Review of medium- and high-resolution satellite images show that the failure was phased, with an initial failure and then a subsequent failure at least two days after 9 March 2018. It also highlights what might be construction activity associated with a dam raise prior to failure.
Ground motion over mine sites, while an everyday occurrence, may represent hazards that need to be identified and monitored over time. An accurate and regularly updated overview of surface movement over mining operations is therefore critical as part of an ongoing risk assessment program. By having a complete picture of ground stability, movement patterns which represent potential geotechnical hazards to safety and mine operations can be identified and tracked over time. From routine monitoring to highfrequency updates, interferometric synthetic aperture radar (InSAR) technology is increasingly being used to identify a wide range of movement patterns which may be of concern to mine operators and geotechnical engineers. Recent advances in radar image processing algorithms, combined with an increase in the number of satellite systems launched into orbit, have resulted in improvements in the ability of this technology to capture complex and rapid displacement. In particular, the ability to characterise rapid and sudden motion (metres of movement) has increased the utility of InSAR from a practical standpoint in characterising geotechnical hazards. Further exploitation of 2D monitoring approaches in capturing vertical and horizontal movement, particularly for producing displacement vectors along cross sections, can also provide additional insights into hazard characterisation. Key differences between the ability of highresolution imagery to capture complex and rapid deformation in comparison to low-resolution (but freely available) Sentinel imagery are also touched upon. This paper will focus on the practical application of InSAR technology to monitor mine sites around the world, illustrating how new processing approaches and data sources are used in the identification of geomechanical risks that are typically of greatest concern from both an operational and safety standpoint. Examples of results over an active mine site will be shared and a particular emphasis will be placed on selecting the right InSAR tool for helping geotechnical engineers best manage risk due to movement.
Topics include the physics of remote sensing, data sources, image processing, and preparation of data for inclusion in a geographic information system (GIS) for further analyses. A summary of former and current Denver Office remote sensing studies is appended to show the variety of possible topics.