The Darker side of real-time monitoring instrument in slope stability

Radar technology used widely in a variety of fields for several decades and has been found also suitable for mining applications. In the early 90s, it has been modified as per the requirement of mining to detect ground movement. And now it is very much effective to detect as well as predicting slope failure. This technology has been proven distinctive advantages over conventional methods in its ability to cover large areas on the surface for true two-dimensional monitoring day and night in almost any weather and atmospheric dust. Further, the adoption of modern wireless communication devices has resulted in practical integrated circuits for electromagnetic frequencies which are used in Radar for continuous monitoring of pit and dump slopes.

Although it has many advantages over the conventional method of monitoring, it has a few critical disadvantages also—

1. This radar technology only detects surface movement.

As the fundamental of radar technology depends on the reflection of the magnetic wave from the slope surface wall. As per the magnetic wave theory and radar technology-the phase difference in between the waves of two consecutive scans is the deformation of the slope wall. Hence it has nothing to do with the movement or events inside the slope surface. That’s why it never detects any event or deformation of subsurface. There are many instruments in the mining industry- i.e. Digital bored Inclinometer which can detect subsurface movement (obviously these instruments have also some limitations).

• It measures only the ‘line of sight (LOS)’ movement.

The radar only detects the line of sight movement, how much the slope wall is moving towards radar or away from the radar that radar can detect. It can not determine 3D movement. On the other hand prism technology can detect 3D movement in 5 different directions, X, Y, Z, Horizontal Direction (HD) and Slope Direction (SD).

• If the slope is covered with vegetation then it cannot determine any movement

Radar signal required a solid surface to reflect the wave properly. And the movement of plants, leaves, and vegetation will be read by the Radar as the slope deformation. In the mining industry, government and statutory guidelines are there to cover every matured slope with plantation. So if mine management follow the statutory rules perfectly then Radar technology is of no use for dump slopes. Active slope can not be monitored because of machinery activity and matured slope can not be monitored because of vegetation.