Some insights on tailings dam monitoring with ground-based interferometric radars

 GroundProbe Global Practice Lead – Geotechnical Advisory, Albert Giovanni Cabrejo Lievano

Tailings dams go through different phases regarding monitoring with radar:

1. Construction—The initial dropping of materials looks chaotic, evidenced by a loss of coherence. Deformation readings during this period are not reliable with radar. This is just the phase in which the dropped materials look for their angle of repose, which is an incoherent movement to the radar.
2. Primary Settlement—Once the angle of repose has been reached, the coherent phase of the deformation process starts, so it will be possible to measure displacements again with regained reliability on the radar readings. These displacements start fast but go into regressive mode as the material is going through a stabilization process. Regressive plots are expected from the radar, but if the displacement happens too fast initially, it could still be coherent but ambiguous. Movement away from the radar very early is likely to be false.
3. Secondary Settlement—During this period, the tailings dam undergoes a densification process. It will lose volume and contract while gaining density. As a result of this process, the surface of the tailings dam will slowly increase its distance to the radar. With every scan, the radar signal has to travel a little longer distance to reach the dam surface in its new densified position. This will look like movement away from the radar. Regressive plots away from the radar are expected.

I have also seen seasonal movements on tailings dams and hydroelectrical dams. These are typically related to the push of the water head upstream during rainy seasons, the subsequent reduction of pressures during drier seasons, and reduced water levels upstream. Understanding the noise base level of the structure is important to avoid unnecessary concerns (alarms).

The radars suffer on vegetated tailings dams due to the vegetation’s interference with the radar signal (loss of coherence). After years of working with tailings dams around the world, we have identified the 24-hour averaging time window for interferometry as a viable methodology to monitor these structures. This has allowed us to detect displacements similar to the displacement rates detected with InSAR.

— Albert

Example of a reinforcement project of an upstream tailings dam monitored with an SSR-SARx by GroundProbe

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