The University of Pretoria (UP), in collaboration with Anglo American, recently established a top-of-the-range mobile soils testing laboratory for the purposes of assessing the strength of samples of mining waste – known as mine tailings or slimes – on site.

The laboratory, housed in an eight-ton truck, will enable sensitive soil samples to be subjected to a range of sophisticated tests in the vicinity of the area they are recovered in. As a result, sample disturbance associated with long-distance transport to laboratories will be avoided through the use of this mobile facility.

The eight-ton truck housing the laboratory is the first time that equipment of this nature has been assembled in a mobile unit.

This mobile laboratory, which was launched on 26 October 2023 at UP’s Engineering 4.0 complex on Hillcrest Campus, marks the first time that equipment of this nature has been assembled in a mobile unit.

“Tailings engineering is a rapidly advancing field of research around the world,” says Professor SW Jacobsz, a lecturer in the Department of Civil Engineering in the Faculty of Engineering, Built Environment and Information Technology. “In addition to existing research facilities, such as the only active geotechnical centrifuge in Africa, this mobile laboratory places UP in a unique position to contribute significantly to advance the state of the art in the important field of tailings engineering.”

Mine tailings (or slimes) refer to a mixture of ground-up ore and water from which precious metal like gold is extracted, thereby leaving vast amounts of this waste product. This sludgy material is disposed of on what is known as tailings (or slimes) dams.

Principal engineer at Anglo American Moseli Motselebane (centre) and other guests look on as the mobile soils testing laboratory is launched.

“This very soft mud is used to build the dam higher and higher,” Prof Jacobsz explains. “However, if you build it too fast without allowing the mud to dry properly, you get stability problems. It is our purpose with this lab to test tailings samples from these dams to determine whether the materials forming these dams are of adequate structural strength.”

Soil testing capability important to the mining industry

Driving a sample of this very soft material many kilometres to Pretoria to a soils laboratory will completely disturb it, he adds.

“It is difficult to transport a soft tailings sample intact, so we’ll drive the truck to the dam, take a sample and carefully walk it into the laboratory without vibrating it. That way, we can test a higher quality sample and will come to know the material’s true properties, which allows for more accurate assessment of the stability of tailings dams.”

The soil testing capability brought about by the new mobile laboratory is especially important to the mining industry, which is under intense international pressure to manage the stability of tailings dams to the highest standards possible. 

Mobile laboratory coordinator Vian Venter shows guests around the facility.

Unstable tailings dams could have grave consequences for the people living nearby and for the environment. The collapse of the Jagersfontein Developments tailings dam in the Free State last year was a devastating case in point, causing fatalities, destroying hundreds of homes and contaminating natural resources.

“In Brazil, in 2015 and 2019, there were massive collapses, with the most recent one killing 270 people,” Prof Jacobsz adds. “It’s absolutely unacceptable and not something that can be tolerated. These dams are often close to where people live, so it’s crucial that stability is adequate.”

The laboratory is equipped with four advanced triaxial test systems, two dynamic cyclic simple shear systems, an automated oedometer system and ancillary equipment. In addition to enabling the state of tailings dams to be assessed from the highest quality samples, the availability of cutting-edge equipment will significantly advance research into tailings behaviour.

UP, Anglo American partnership

Triaxial test systems apply all-round confining stress and downward pressure to a cylindrical sample, Prof Jacobsz explains. When the sample deforms, you’ve reached the strength of a sample. On the other hand, dynamic cyclic simple shear systems deform a sample by forcing it to tilt.

A triaxial test on a soil sample with local strain measurement and bender element testing underway.

“To my knowledge, this is the first time that a laboratory of this quality, with this collection of testing equipment, has been made available to the mining industry,” Prof Jacobsz says. “In Australia, they’ve taken a single triaxial set-up to a mine, but they don’t have a truck. UP has four triaxial devices in the truck and two dynamic cyclic shear apparatus, which are highly sophisticated. It’s the better of the two methods, and very costly, so we were very fortunate that Anglo American was prepared to fund that.”

He worked with Anton Bain, head of Residue Facilities at Anglo American, and his team to establish the facility.

“They funded everything, including the salaries of two full-time technicians who have been employed by UP to run the lab,” Prof Jacobsz says.

He adds that UP will be testing Anglo American dams first, and that once there is a gap in the programme, they may be able to work on dams for other mining groups.