Topographical correction – visualising beyond the surface for safety

By Sharyn Macnamara | All images supplied by Reutech

Reutech Mining, an engineering company globally known for its innovative mining solutions, is seeking to mitigate Falls of Ground (FOG) risk through rapid development using off-the-shelf technology in a revolutionary way. Rock hazard identification and the monitoring thereof is the company’s specialty.

The work environment underground is dark, hot, damp and restricted, and miners must enter an excavation after a blast to examine it and make it safe. This task becomes the responsibility of two miners at the beginning of each shift, clad in heavy PPE and equipped with two cap lamp spotlights to provide the only illumination. They tap the excavated walls with a pinch bar to identify and remove loose rock before bolting and netting is installed to prevent FOG. This is a risky business. Advances in technology are urgently needed to improve these conditions.

In February 2023, the Reutech team won the local Rock Hazard Identification and Safe Removal Innovation Challenge run by the Mandela Mining Precinct, the Minerals Council of South Africa, and champion mines – Sibanye-Stillwater and Impala Platinum – in a quest to better detect and monitor FOG – historically one of the biggest causes of fatalities on South African mines.¹ Reutech’s geotechnical engineer, Heinrich Greeff took African Mining through the company’s proposed innovation and its potential development path.

Making the invisible visible

Greeff explained that after a blast, fracturing and rock hazards can sometimes be located in the skin of the excavation, where they are visible. These hazards are typically addressed through conventional visual inspection, followed by barring to attempt to remove loose rocks that pose a FOG hazard.² However, it is within the scope of unseen structures – one to multiple metres deep within the rock mass – where Reutech’s current ground penetrating radar (GPR) enables the identification of structures to be managed to prevent potential unidentified, beyond surface, FOG issues caused by structures not observed easily on the surface of the excavation.³

GPR works by sending a waveform into the rock mass, which is then reflected back by structural changes in the rock. The company currently uses GPR tech and RF (Radio Frequency) in a patented hand-held device they already supply to the industry – the SSP (Sub Surface Profiler) designed specifically for underground mining operations. Its light-weight design enables one-handed operation by one person in much the same way as a paint roller, said Greeff. The data collected is wirelessly transmitted and processed in real-time, giving instant feedback on rock structures to a second operator underground, reading the feedback digitally on a tablet while scanning is taking place. The objective is to enable directives following the scanning to achieve optimal utilisation of roof support mechanisms in an environment where every second counts.

“The current tech allows us to pick up structures deeper within the rock mass to alert the team to these, as it relates to the possibility for instability, such as gravity falls and excavation drift, which may ultimately be exacerbated by seismic energy,” Greeff explained. “A solid dark mass is nothing to worry about, while the red highlights the area of issue.”

Tech challenge and solution

However, traditional GPR has two practical challenges. One is that data interpretation can be tricky for the untrained eye, and two, an uneven rock surface, which is the reality most of the time, distorts the scanned image, making identification and therefore assessment more difficult.  Easy data interpretation is therefore the new end goal, as typically, distortion of the scanned structure occurs because while the SSP scans across the rock surface, the distance that the GPR is away from the structure being scanned changes over time, thus warping the image.

Reutech has proposed ‘topographical correction’ as an add-on to the current SSP technology to enable a clearer picture with the objective of making data interpretation easier and decision-making faster by the user. In mapping the topography of the rock mass, as one scans with the SSP, one assumes it is scanning a single line, and that line should resemble the topography scanned, which is not the case because of the reality of an uneven rock surface. The idea is to map the vertical movement of the SSP and, on the back-end, record the inertia and movement of the SSP. The result will be in an inertia measurement unit (IMU) to record the movement of the platform while combining it with data received from a scanning GPR  antenna. This allows the position of the platform, versus the object it is observing, to be plotted in parallel.

Direct and immediate benefit

The direct and immediate benefit of the SSP is the ability to identify rock hazards beyond the excavation skin that are not visible to the naked eye. This is achieved through the production of a graph that depicts the roller as it is dragged across the rock surface, with the x-axis recording the distance scanned and the y-axis recording the depth into the rock mass of the structure. The red in the image indicates a reflected structure, which is interpreted as a typical fault or crack in the rock.

“The structure identified in this particular image supplied could create a wedge that falls out or a plane where the rock face could dislodge. Depending on the width of the excavation, this could create a fairly large FOG. Now that the mining team is aware of the deeper structures, not observable on the excavation skin, but observed with the help of the SSP and topographical correction, the structure detected can be fully assessed and understood. Action can then follow to stabilise the area with required support, like bolting. In such a case, the SSP would be used to enable the assessment of structures beyond the supported beam. It becomes a design verification tool used to assess whether or not the support design is sufficient.”

Greeff explained that there are further developments planned for the SSP, such as 3D imaging, which will build on the foundation of getting the ‘zero line’ – the bottom of the scan – correct with compensation for the movement across an uneven surface. “The idea is to give miners doing visual inspections a powerful but light, fully portable, connected, stand-alone tool and system, which allows them to observe beyond the rock surface to identify rock hazards,” said Greeff.

Because Reutech innovates using off-the-shelf technologies, they are able to rapidly innovate. The SSP has two distinct categories in which it can be further developed – data acquisition and data analysis. Topographical Correction makes it easier to interpret the data, and further developments in data interpretation will involve factors such as automatic settings, calibrating permittivity, location and structure identification through machine learning.

Herewith a direct comparison of two SSP scans overlain onto a photo of the area scanned – three benches. Scan 1 – with a flat top-edge finish – shows the result without topographical correction; while Scan 2 ­– staggered at the top with topographical correction applied – indicates the same scan path and red areas showing geological structures, which are clearer and connected now, making the holistic analysis of these structures less complex and easier to understand.

The proposed topographical correction concept promises ground-breaking visualisation of rock hazards at depth, enabling dynamic decision-making and immediate risk reduction, which could save lives. Going forward, this could involve automated alerting with additional functions based on operator input, such as the length of bolts. The software will then indicate if the support structure will be sufficient to pre-empt any FOG due to possible insufficient support.

Overall, the SSP promises to be a game-changer for the mining industry, providing a powerful tool for identifying rock hazards and reducing risks in real-time.

References:

1. For more detail, go to https://www.africanmining.co.za/2023/02/24/sa-industry-collaboration-supports-tech-innovation-in-rock-hazard-identification-safe-removal/
   The Rock Hazard Identification and Safe Removal Innovation Challenge was undertaken as part of the Fall of Ground Action Plan (FOGAP), a programme developed and approved by the Minerals Council’s CEO Zero Harm Forum, in conjunction with the Mandela Mining Precinct’s Advanced Orebody Knowledge (AOK) programme. The FOGAP’s objective is to eliminate fall-of-ground fatalities, while the AOK programme seeks to improve geological confidence at and beyond the rockface.
2. Scaling, also known as barring down is the art and function of making the ground safe using a scaling bar to locate and remove loose rock from the walls, face and backs of the workplace.  In manual scaling, loose or potentially unstable rock is prised off the rock surface with an appropriate scaling bar.  The ability to correctly “read the ground”, or assess the ground conditions, is essential to all people carrying out scaling, no matter how small the area to be scaled.  Manual scaling is potentially one of the more hazardous activities in underground mining.
   https://www.dmp.wa.gov.au/Documents/Safety/MSH_G_UGBarringDownAndScaling.pdf
3. The SSP has been commercially available since 2016. The company currently trains users on how to use the SSP unit and customises training on how to interpret the data, per mine and the prevalent hazard-type experienced in that particular mine’s topography. The mine ground control or rock engineers with the knowledge base within the mine’s design specifactions manage the process and the Reutech team is sometimes required to assist with troubleshooting after training has taken place.

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