CASE STUDY

Tracking Tailings Wall Movement in South Africa Remotely with InSAR

Ground Engineering Awards 2026 Finalist in the Technical Excellence Category

PROJECT IMPACT

Monitoring for over 5 years: Sentinel-1 SBAS-DInSAR analysis assessed ground deformation at a Tailings Storage Facility (TSF) from February 2021 to June 2026, providing a continuous long-term record of ground displacement behaviour.
Identified up to 100 mm of cumulative Line-of-Sight (LOS) displacement, with the highest displacement recorded along the facility’s central wall and approximately 80 mm observed along the facility’s northern wall.
Clear transition from acceleration to stabilisation: Monitoring captured a distinct shift in ground behaviour, with deformation accelerating from around September 2024, slowing significantly from February 2025, and progressing toward stabilisation at selected locations by early 2026.
Assessed movement patterns via continuous spatial monitoring. DInSAR provided spatially distributed deformation measurements across the TSF, enabling assessment of movement patterns across individual embankment zones alongside a detailed point-based time-series analysis.
Evaluated differences in deformation magnitude and temporal behaviour, analysing selected scattered points across the western, northern, central, eastern, and southern walls of the tailings facility.
Detailed wall-by-wall assessment: Selected scatterer points were analysed across the western, northern, central, eastern and southern walls, enabling assessment of localised variations in deformation magnitude and temporal behaviour.

Project overview

Understanding the long-term behaviour of the ground and infrastructure is critical to assessing ongoing performance and supporting risk-informed management of tailings storage facilities.

Geofem was commissioned by TSF Risk Solutions to undertake a satellite-based ground displacement assessment of a Tailings Storage Facility using Differential Interferometric Synthetic Aperture Radar (DInSAR).

"The objective was to assess historical and ongoing deformation, identify areas exhibiting persistent or changing movement behaviour, and improve understanding of spatially variable settlement across the facility."

Geofem’s for·see Mining assessment utilised Sentinel-1 satellite observations from February 2021 to June 2026. The monitoring period was divided into two processing segments—MP1 (February 2021–April 2023) and MP2 (May 2023–June 2026) — with the resulting datasets subsequently combined into a single, continuous LOS displacement time series.

The challenge

Understanding the performance of a large TSF requires more than identifying whether movement is occurring at a single location.

Deformation can vary substantially across different sections of an embankment, and movement behaviour evolves over time.

"This inevitably required a monitoring approach capable of evaluating both the spatial distribution and temporal evolution of ground deformation across the entire facility."

The study area is characterised by complex topography, with elevation ranging from 1,580 to 1,639 m along the west–east transect and 1,592 to 1,644 m along the north–south transect.

The assessment therefore needed to capture spatial variations in deformation across the engineered structure, by distinguishing these from ongoing tailings wall consolidation settlements.

Understanding how displacement behaviour evolved over time was also crucial. Rather than relying on a single average velocity measurement, the analysis needed to identify persistent deformation trends, changes in movement rates, periods of acceleration and indications of stabilisation, drawing on a long-term, multi-temporal satellite dataset.

Figure 1: Cumulative Line-of-Sight (LOS) displacement on the central wall of the Tailings Storage Facility from February 2021 to June 2026, showing spatially variable deformation concentrated around the TSF embankment.

The Geofem approach

Using the capabilities of for·see Mining, Geofem applied Differential Interferometric Synthetic Aperture Radar (DInSAR) using the Small Baseline Subset (SBAS) methodology.

"Sentinel-1 ascending-orbit SAR data were processed over the 5.5-year period from February 2021 to June 2026 to establish a consistent Line-of-Sight (LOS) displacement record."

To optimise coherence and increase scatterer density, the dataset was split into two monitoring periods: MP1 (February 2021–April 2023) and MP2 (May 2023–June 2026). The processing results were subsequently integrated to form uninterrupted LOS displacement time series for representative target locations.

The evaluation was structured along individual TSF embankments. DInSAR investigation was implemented across the western, northern, central, eastern, and southern walls.

This wall-by-wall spatial segmentation enabled identification of differences in deformation magnitude and temporal behaviour, characterised and tracked over time.

The results presented in this case study focus on observations from the central wall, providing a detailed view of deformation behaviour at this section of the facility.

Geofem analysed the resulting time series to identify persistent trends, changes in movement rates and periods of increased deformation.

"Spatial deformation mapping complemented this temporal analysis, placing observed movement directly into the context of TSF geometry."

The combined spatial and temporal analysis provided an area-wide view of deformation, while also enabling detailed assessment of individual monitoring locations. This approach allowed changes in ground movement behaviour to be identified, characterised and tracked across different sections of the TSF throughout the monitoring period.

Figure 2: A selected DInSAR scatterer point in the central wall of the TSF.

Figure 3: LOS displacement time series for monitoring point P7 on the central wall of the TSF from February 2021 to June 2026, showing changes in displacement behaviour during the monitoring period.

Results

Geofem’s analysis revealed spatially variable deformation across the TSF. The highest displacement magnitudes were concentrated along the embankment zones, while the surrounding ground remained relatively stable.

Central Wall: Exhibited the highest cumulative displacement, with the selected monitoring location on the central wall (Figure 2) reaching approximately 100 mm of cumulative LOS displacement over the 5.5-year monitoring period (Figure 3).
Northern Wall: Showed substantial ground movement, with cumulative displacement reaching approximately 80 mm at selected locations along the wall.
Western Wall: Experienced movement exceeding 70 mm at selected locations by June 2026, with a mean annual velocity of approximately 17.1 mm/year during MP2.
Eastern Wall: Remained relatively stable during MP1 and early MP2, before developing a downward displacement trend from approximately September 2024. By the end of the monitoring period, continued downward movement was observed along parts of the eastern wall, while other locations exhibited an upward trend.
Southern Wall: Displayed complex deformation behaviour, with selected locations developing sustained downward movement after early 2022. Cumulative displacement exceeded 80 mm at one location, while other sections exhibited lower-magnitude movement and changes in displacement direction during the monitoring period.
Temporal Kinematics: Along the northern and central walls, higher displacement rates were observed from approximately September 2024, followed by a reduction in movement rates from around February 2025.

Geofem Insights

Operational TSFs are evolving structures. It is common to have movement along the entire lengths of tailings dams throughout their operation. This is normal and is due to the ongoing consolidation of tailings and underlying foundation soils as dams are raised and tailings deposited.

Precursor movements indicative of an impending collapse may be masked by these ongoing consolidation settlements. This makes careful interpretation of the movement data by experienced geotechnical engineers crucial to the success of a monitoring campaign. This can identify the tell-tale signs of potential collapse among the general movement.