BME’s Optimisation Initiative Saves Mine Millions

BME – Media Release on Cost Reduction through Pre-splitting and High-Wall Improvement

When a South African coal mine faced high-wall challenges that raised its operating cost, BME’s technical team was able to design and implement a modified pre-split design that cut costs while retaining optimal fragmentation.

The mine had experienced problems with poor blast performance and geological issues at its high walls.

According to BME technical services manager, Tom Dermody, excessive burdens, mechanical over-digging, and poor pre-split performance were factors behind the unfavourable high-wall conditions. He adds that previous attempts to address the issue had added additional face row holes to remove the excessive burden, but this resulted in increased drilling and blasting costs per cubic meter.

A typical blast size on the mine is 540 holes in each 300-metre blast strip, with a bench depth of 23 to 30 metres. Blasting operations follow a methodology of full chevron and half chevron initiation sequence, with pre-splits executed in advance.

“Our technical services team conducted a thorough study of blasting operations and identified key areas for improvement. We focused on pre-splitting and excessive burden management,” he explained.

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Pre-splitting is a technique in mining operations that aims to enhance rock fragmentation and overall blasting efficiency. It involves creating a stable zone along the rock surface before the primary blast, which allows for controlled fracturing and helps to minimise the risk of overbreak.

He emphasised that this technique also contributes to maintaining a more uniform material size, which is of utmost importance in mining operations.

“The pre-split design changes we introduced included adjusting the split factor, changing the pressure curve, and increasing the explosive charge per hole. The split powder factor of the pre-split drill holes was increased from 0.3 kg/m3 to 0.8 kg/m3, resulting in more favourable pre-split outcomes,” explained BME Senior Technician technical engineer Frank Hattingh.

He pointed out that optimised burden relief is crucial for optimal fragmentation during blasting. Excessive burdens will produce poor fragmentation, reduced blast movement and damage to high walls.

“In the past, a common method of trying to manage poor fragmentation was to introduce additional drill holes – to increase the powder factor in the front row of holes. This was an additional 60 holes or 1800 metres of drilling on a typical blast. The modification in the pre-split design allowed the removal of these crest holes, resulting in an 11% reduction in drilling meters per blast,” Hattingh said.

BME’s intervention at the mine highlighted the importance of pre-splitting in mines, which serves as a strategic technique to optimise rock fragmentation and overall blasting efficiency. By creating a stable zone along the rock face before the main blast, pre-splitting allows for controlled fracturing, minimises the risk of overbreak and maintains a more uniform material size.

“Through this modified pre-split technique, we assisted the mine in achieving more precise control of high wall safety and performance. The main cost saving was through removing the crest holes, which saved the mine nearly R8 million in drilling, explosives and accessories over a 12-month period and additionally presented a possible > R230 million in savings across the customer’s value chain,” concluded Dermody.