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Tailings dam monitoring: In-ground and above-ground technologies
One of the key challenges currently facing the mining sector is the industry-wide initiative to implement the most effective and efficient methods for monitoring tailings dams. While tailings storage facilities (TSF) are a necessary component of virtually all major mining operations, these facilities carry a significant amount of risk. The rupture of tailings dams and the leakage of mining by-products can result in serious consequences for mining firms, surrounding communities, and the environment. Tailings dams must be monitored carefully and continuously to minimize the risk of costly failures.
The initiative to implement better methods for monitoring tailings dams has become more urgent following the 2020 launch of the new Global Industry Standard on Tailings Management. This standard is designed to prevent major failures and improve the overall safety of tailings facilities across the globe, with a target of zero harm to people and the environment. Meeting this objective will require a technology-driven effort to utilize the most robust methods for monitoring tailings dams.
Mining companies can access a suite of monitoring technologies designed to detect and warn of changes in key geotechnical parameters, including ground displacement, pore pressure, and dam seepage. A monitoring system must be tailored to the specific characteristics of a tailings dam. As there is no single “one size fits all” method, mining operators must understand the advantages and disadvantages of the available technologies in order to build robust monitoring systems that comply with evolving regulatory standards.
The following is a description of the roles that various technologies and methods will perform in effective TSF monitoring systems going forward:
Interferometric Synthetic Aperture Radar (InSAR) is a technology that identifies displacement over time by comparing multiple pairs of satellite radar (SAR) images. Specialists use the phase information of these images to create interferograms that reveal the degree of displacement that occurs between image acquisition dates. Displacement data results are shown visually over satellite imagery, allowing clients to readily identify the precise areas where movement is detected. Results also reveal the extent of movement in addition to indicating when it occurred. Depending on which radar satellites are used, new images are acquired every two to twelve days. As a highly complex technology, InSAR relies on experienced specialists to produce actionable information from satellite radar images. These specialists generate timely, trusted data that allow clients to make risk-informed decisions.
One significant advantage of InSAR over optical satellites is that radar cuts through rain and clouds while remaining effective at night. Although the atmosphere can be a data contaminant, advanced processing techniques allow specialists to remove atmospheric signals and other contaminants from the data. Due to these strengths, InSAR has 98% image acquisition reliability. Data collected by InSAR is highly precise; it can detect displacement as small as 1 to 2 mm over a year. InSAR images can cover large locations, analyzing areas over 1,500 square kilometres. Another advantage of InSAR is that its sensing is performed remotely without requiring in-person inspections. However, a tailings dam monitoring system based on InSAR is most effective when combined with ground instruments.
Pore pressure monitoring
As pore pressure has a direct relationship with the subsurface movement behaviour in soil, Piezometers are one of the most important instruments for monitoring the field performance of TSFs. Piezometers installed into the TSF slopes can highlight perched water level tables and areas of trapped water. This is important as the increase in pore pressure reduces the shear strength of the soil and is a precursor to failure. This data can give an early indication of problems before they can be seen even by InSAR.
TSF designers and operators can use piezometer data to help plot flow lines that can inform and guide the site’s monitoring strategy and safety risk assessment. Determining the TSF’s phreatic line and seepage pressure is essential to analyze slope stability.
Read Piezometers: A Guide to learn more.
Automated remote in-ground deformation monitoring
SAAV Extend—Measurand’s latest innovation addresses the challenges of continual deformation monitoring during the raising of tailings dams. Inspired by direct feedback from clients in the tailings and mine waste sectors, SAAV Extend provides a continual deformation profile throughout multiple dam raises with unparalleled ease of installation and data interpretation.
These sensors can be configured to perform readings with a data acquisition system that collects deformation data according to scheduled intervals. This allows for the communication of timely sub-surface measurements without having to rely on manual collection, which can be time-intensive and prone to human error.
Total Earth Pressure Cells
Total earth pressure cells are designed to measure stress acting on plane surfaces. These devices can be used to monitor total pressure in tailings dams. They are built from two circular stainless-steel plates that are welded together at their peripheries. De-aired glycol fills the annular space between these plates. A closed hydraulic system is formed by connecting the cell to a transducer with a stainless-steel tube. Stress acting on this system produces a signal that can be read remotely on data loggers or portable readouts units.
These devices have the advantage of monitoring pressure, which is often the source of displacement in tailings dam embankments. By identifying areas that may be prone to future movement before displacement occurs, total earth pressure cells are an integral part of a robust tailings dam monitoring system.
GAA Slope Monitoring System
Geo-Acoustic Aware (GAA) sensors are designed to detect acoustic emission stress waves, indicating slope displacement. These sensors can be used at shallow depths to provide data on the spatial infill of ground movement. In this role, GAA provides a reliable and low-cost alternative to traditional instrumentation, but it can also be used in conjunction with devices such as inclinometers, weather sensors, and piezometers to monitor slow to moderate slope movement rates in tailings dams.
The installation of this system is straightforward and GAA sensors can provide real-time monitoring data when connected to a GAA2820 Data Logger. These sensors, like other in-ground instrumentation, can also be set up to communicate wirelessly over a network, allowing GAA data to be combined with other data sets.
Earthquakes pose a significant risk to tailings dams. Seismic sensors can monitor earthquake hazards by effectively detecting seismic activity. It is possible to engineer these sensors to provide real-time data. Sensors equipped with magnetometers and accelerometers can also warn of movement in the walls of tailings dams.
A disadvantage of these sensors is that they can produce false positives when used near active mine sites since they will also register the movement of heavy equipment and activity caused by blasting operations. Effective use of seismic sensors in a monitoring system at an active site requires taking false positives into account when analyzing data sets. These sensors are more efficient when used to monitor tailings dams that are not in proximity to sites with heavy plant movement or blasting.
Achieving zero harm
To achieve the objective of zero harm set by the Global Industry Standard on Tailings Management, the mining industry must utilize the latest technological solutions to build monitoring systems that are effective at identifying potential risks before the event of failure. The most robust systems take a holistic full-site approach to monitoring. These systems integrate remote radar detection with real-time data obtained from sensors installed at the site.
A Platform Approach to Monitoring TSF
3vGeomatics is a company that specializes in InSAR monitoring. 3vG, along with RST Instruments, Measurand, and Syscom Instruments make up a platform of companies that lead the way in providing solutions for geotechnical data and instrumentation needs. Combined, this platform is an industry-first surface and sub-surface data monitoring and analysis solution with a full global reach through underground sensors, cloud-based data and satellite technology.
3vG offers clients rich intelligence that assesses the stability of tailings dams, communicates the occurrence of movement, and produces displacement histories. Rapid reports from 3vG provide near real-time information to clients who require immediate hazard warnings, delivered within 24 hours of each new satellite radar image acquisition. 3vG also offers comprehensive reports derived from the analysis of a complete set of SAR images over a specific area of interest. These reports provide actionable information on displacement trends based on tens of millions of data points.
Contact us to learn more about how InSAR can be combined with ground-based technology to produce the most effective methods for monitoring tailings dams and tailings facilities.
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I’m very happy with the quality of the instrumentation and technical support from RST, as always. They worked with us from the initial stages of the project to ensure that we were fully prepared and equipped to use the RSTAR network for the first time. They delivered everything within the tight project time frame to ensure that there were no delays on site, and the submersible tilt meters looked like new even after over twelve months of being submerged in Thames water!
-Richard Lipscombe, BEng (Hons), Director & Principle Consultant - RL Geotechnical Ltd