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

Tailings dams go through different phases regarding monitoring with radar:

1. Construction – initial dropping of materials, which look chaotic, and it is evidenced by loss of coherence. Deformation readings during this period are not reliable with radar. This is just the phase in which the dropped materials are looking for their angle of repose. This 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 readings from the radars. 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 at the beginning, it could still be coherent, but ambiguous. Movement away from the radar very early is likely to be false.?
3. Secondary Settlement – in this period the tailings dam undergoes through a densification process. It will loose volume, contract, while it gains density. As a result of this process, the surface of the tailings dam will slowly increase the distance to the radar, as 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 hydro-electrical dams. These are typically related to the push of the water head upstream during rainy seasons, and the subsequent reduction of pressures during drier seasons and reduced water levels upstream. It is important to get to understand the noise base level of the structure to avoid unnecessary concerns (alarms).

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