Located in the heart of the Ashanti belt, our project starts at an open-cut gold mine with two active pits. Both geologically complex, characterised by competent rock intersected by repetitive shear zones – a phenomenon that creates significant highwall instability risk.

One of these pits has a particularly sensitive history, having experienced large-scale slope failures in the early 2000s severe enough to result in a temporary production stoppage. These recurring shear zones and the site’s structural complexity make wall control blasting a critical operational discipline in managing this risk.

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For the longest time, like many mines, the operation relied on pre-split blasting as there go-to strategy for high-wall protection. Which they would implement religiously ahead of production blasts. By creating a stress relief crack, pre-splits would isolate the wall from the production shot, minimising damage. This however was not the case here where pre-split energy itself was causing back-break rather than preventing it.

The frequency and severity of the back-break was so significant that in some cases entire berms where removed. In others, localised slope failure and minor slips were also noted.

These conditions created ongoing concerns around safe pit access for personnel and equipment. Exposure of shear zones further increased geotechnical risk, requiring continuous monitoring and remediation where possible.

In addition, steeper wall profiles regularly required berm widening, placing additional pressure on hauling productivity due to the increased volume of waste material needing to be moved. The resulting wall profiles also prevented the operation from consistently achieving the designed bench face angles, creating non-compliant pit geometry and negatively impacting the overall economics of the mine.

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To support the operation in addressing these issues, SRK was engaged as a technical advisor. Together, an initial wall control design was developed incorporating trim blasting into the existing methodology, using trim shots fired behind a pre-split with a shortened buffer row. Initial blasts using this method did show some improvements, but with trim holes still requiring up to 6 metres of emulsion charge in a 9-metre bench, this design was abandoned (in its current form) as it introduced too much energy into the final wall.

Having shown some promising signs, the consulting team then identifed trim blasting with airdecks, as offering the perfect solution. By replacing the upper emulsion column with an airdeck, the total explosive energy in each hole would be significantly reduced,concentrating the remaining charge at the toe and controlling the energy distribution along the column. Limiting the blast energy reaching the final wall. This approach would allow trim shots to be fired without pre-splitting, reducing both complexity and cost.

Lead by Chief Geotechnical Engineer, Solomon Quaye, Blastbags were incorporated into the trim blast design across all three trim rows at both pits. With a hole diameter of 102 mm, Blastbag sizes were selected accordingly. Explosive charge weights were adjusted based on UCS (Uniaxial Compressive Strength) and rock density to ensure appropriate energy levels for effective rock breakage at each row position.

With two separate blast contractors operating at the respective pits, the solution would be introduced to both locations at the same time.

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At Pit A, the improvement was visible immediately. Crest lines became clearly and cleanly defined – even without pre-split blasting. Back-break beyond the design crest was effectively eliminated in the majority of blast blocks, and where overmine did occur it presented as a widened berm rather than damage extending back into the wall. Berm retention improved to approximately 85–90%, with bench face angles now consistently achieved at 65° and minimum 5-metre berm widths maintained. This steeper achievable angle directly reduces the strip ratio, improving the economics of the pit. No significant geotechnical incidents or wall instability events have been recorded since consistent Blastbag application began.

At Pit B, wall face profiles have also improved – cleaner faces, fewer overhangs – but results have been less consistent due to contractor compliance variation rather than any limitation of the solution itself. This however, through an ongoing programme to improve contractor consistency, is showing steady improvements.

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