TSF Failure Analysis | Jagersfontein post-failure investigation

TSF FAILURE ANALYSIS | JAGERSFONTEIN POST-FAILURE INVESTIGATION
By M. van der Spuy (GeoGroup CPT Manager) and S. Prinsloo (Terra Monitoring Operations Manager)

Our technical team recently attended the Jagersfontein Tailings Dam Failure Investigation and Dam Break Analysis, hosted by the University of Pretoria. Our teams gained some valuable insights from this investigation. The failure at Jagersfontein remains one of the most important lessons for the tailings industry in South Africa. The official investigation published by the Department of Water and Sanitation and led by Prof. S.W. Jacobs made it clear that tailings storage facilities (TSFs) cannot rely on design alone. Continuous understanding of how a dam behaves in real time is essential to manage not only TSF’s, but the risks thereof too.

Key takeaways from the lecture and report include the value of satellite imagery and monitoring of pore pressures and embankment settlement or movement. As seen in this case study, a tailings dam does not fail overnight. It usually shows subtle movement first. The challenge is that these movements can be extremely small, often millimetres. Luckily, modern systems can detect this early such as GNSS load-sensing technology which measures precise surface displacement. Paired with Inclinometers or ShapeArrays which measure lateral movement inside the embankment. Possible failure zones could be identified, and in cases of settlement, settlement cells can measure vertical compression within the dam. All this paired with Satellite-based InSAR imagery, can detect broader, slow-moving deformation over large areas.

Based on the unseen factors which can be monitored continually, tailings behave very differently depending on how much water pressure exists between soil particles. When pore pressures increase, the material can lose strength. In undrained conditions (where water cannot escape quickly), strength can drop rapidly and sometimes suddenly. This is where Vibrating Wire Piezometers (VWPs) play a critical role. They measure water pressure inside the dam. By continuously tracking pore pressure trends, operators can see whether conditions are becoming unstable long before visible signs appear.

While monitoring tells us how a dam is behaving in real time, Geotechnical Investigations tell us more about the tailings foundation and what lies within it. One of the critical technical tools in understanding soft or potentially problematic layers is CPTu testing (Piezocone Penetration Testing). Soft, contractive, or loose saturated layers can behave unpredictably under loading. If such layers exist within the tailings or foundation, they may be prone to strain-softening or liquefaction under certain stress conditions. Thus, this sort of testing and sampling via the use of Mostaps can identify soil properties in the field. This can also be achieved through geotechnical drilling and sampling.

However, in getting a more comprehensive understanding of the soil properties, one must commission in-situ Testing as this greatly broadens the understanding of site properties. Coupled with Electronic Vane Shear tests (eVST) and Dilatometer Tests (DMT), a better understanding can be gained regarding the stiffness of specific soil types. Effectively, if done right, the test data will better indicate how much the soil will settle and if the soil is competent enough for purpose. Combining geotechnical understanding, real-time monitoring, and disciplined operational control would proactively identify, quantify, and mitigate potential failure mechanisms.

In closing, risk management through Trigger Action Response Plans (TARPs) and clearly defined procedural responsibilities must be implemented in practice to manage monitoring controls actively. When paired with robust early warning systems linked to actionable technical thresholds, these protocols ensure that data is not just collected, but used to support safer, more informed decision-making. This includes involving potentially affected communities nearby and advocating a realistic and effective evacuation procedure.

The technical complexities of TSF management require a data-driven approach to safety. In response, GeoGroup and Terra Monitoring, provides a turnkey solution that integrates advanced geotechnical investigations—such as CPTu and eVST—with a comprehensive suite of geotechnical instrumentation. By combining equipment supply and installation with high-level technical expertise, we support mine managers in identifying and mitigating potential failure mechanisms through precise data and continuous monitoring.