Geomech Africa was appointed to conduct an extensive in-situ testing campaign at a tailings storage facility. This appointment followed the success of a previous investigation completed at this site where Geomech Africa demonstrated both strong technical capabilities and reliable project execution.
The scope of work consisted of six linear lined out positions around the TSF, with each line containing three test points requiring: Seismic CPTu testing with dissipation measurements; MOSTAP sampling; and electronic vane shear testing (eVST). The testing was executed using a 20-ton track-mounted rig with a 150kN Pagani mast mounted to the bed of the rig. The 20-ton rig was specifically chosen for this task as its mass alone provided the required reaction force without the need for anchoring, ensuring uninterrupted testing.
The seismic CPTu investigation progressed efficiently and without significant operational difficulties, which is scarce in fine, saturated tailings. In total, 506 metres were probed, with termination depths ranging from 31,65 metres in the basin to 3,25 metres on the surrounding benches. Dissipation testing amounted to 6 236 cumulative minutes, and seismic measurements were successfully taken at one-metre intervals throughout. The consistent performance of the CPTu rig facilitated rapid and high-quality data collection across all test positions.
MOSTAP sampling was equally successful. A total of 54 samples were recovered with an average recovery rate of 93 percent, with several positions requiring up to six samples. The deepest sample was retrieved from 30 metres below ground level. The resulting suite of samples provided high-quality material for further laboratory testing and complemented the CPTu data set well.
The eVSTs proved to be the most challenging element of the project. Although GeoGroup had prior experience with eVSTs, they had never carried them out directly from a CPT platform. The initial protected‑housing setup recommended by the manufacturer did not work as planned because the tailings compacted inside the sleeve, preventing proper vane deployment. After discussions between the client’s geotechnical team and GeoGroup’s on‑site Geotechnician, the team adopted a practical solution: pre‑punching holes, which eliminated the need for a drilling rig. Early tests showed that the holes stayed open and stable, enabling a return to the standard eVST method — a process the team was already highly familiar with. This change greatly increased productivity and reduced the testing time by about half. In total, 24 eVSTs were conducted across nine locations of which 20 of them yielded reliable, high‑quality data.
Throughout the project, all activities were carried out safely, and no accidents or incidents were recorded. The investigation ultimately produced a comprehensive set of CPTu, seismic, MOSTAP, and vane shear data, providing the client with a robust geotechnical basis for evaluating the TSF. The successful adaptation of the eVST methodology highlights Geomech Africa’s ability to respond and adapt to technical challenges quickly and effectively. This project further complements Geomech Africa’s reputation for delivering reliable, technically sound in-situ investigations on complex tailings storage facilities.