Scanners & Trackers-->Red Dog Ground Penetrating Radar

Use of Ground Penetrating Radar in South African Mines

Ground Penetrating Radar (GPR) systems have been in use for over 30 years, most commonly in geophysical applications and for locating and mapping buried utilities.

A typical GPR system consists of a control unit and antenna. The control unit creates pulses of radar energy and projects them, via an antenna, into the ground (no borehole needs to be drilled).   As the transmitted radar waves encounter dielectric/permittivity changes in the rock (related to chemical or physical changes), energy is reflected back to the antenna and is recorded and displayed as a radargram by the control unit.

Antenna frequency is related to the physical size of the antenna and is a major factor in depth penetration and target resolution.  A small, high frequency antenna will locate smaller targets, but will not penetrate as far into the surface. Conversely, a larger, lower frequency antenna will penetrate much deeper, but offers lower resolution.

Above: A GSSI SIR-3000 GPR console (foreground) and 400MHz antenna (background). The SIR-3000 is slightly larger than an A4 page and weighs only 4.1kg, whilst the antenna is only 30x30x20cm and weighs 4.6kg.

GPR in mining
Due to advances in electronics and software, GPR has rapidly evolved into a valuable investigative and safety tool for mapping potential loss-of-ground structures and unmapped workings within the underground mining environment. In addition, since modern GPR systems are relatively compact, they can be used without disruption of mining production.

Although early GPR systems were complex and required a highly skilled and experienced operator to collect and interpret data, current systems employ advanced analysis software and improved user-interfaces, making them significantly easier to operate. With a few hours of training and a couple of shifts of hands-on experience, GPR data can now be collected by relatively unskilled operators.

Above: GSSI SIR-3000 GPR console

The radargrams produced by GPR look much like the seismic sections so familiar to most mining geologists and geophysicists and, since GPR data is displayed in real time on the console, critical decisions can (in many cases) be made immediately. More detailed, quantitative analysis can be made in the office using the radar processing & interpretation software supplied.
The radargram below is of the hanging wall at a Bushveld mine, showing structure to approx 5m depth (the image has been flipped so that surface of the hanging wall is at the bottom of the radargram). Data was collected using a GSSI SIR-3000 console and a 400MHz antenna.

Penetration can vary from a few centimeters, to tens of meters, however in the underground mining environment, where there are constraints on the physical size of the antenna that can be deployed, depths of 5-8m are typically obtained. In an opencast mine, where it is feasible to use the larger, lower frequency antennas, depths down to approximately 30m can be obtained.

Currently a number of SIR-3000/400MHz systems are being used in prominent Bushveld mines for the purpose of scanning the hanging wall for potential instability. This application has been very successful and, at the time of writing, there have been no reports of fatalities related to loss-of-ground in mine areas which have been scanned using the GSSI SIR-3000 GPR.

Radar is no longer just a tool for researchers. Now that it’s readily available in South Africa it is a practical tool for underground and opencast mining, and for any other applications where an accurate depth image of the subsurface is required.