Profile
Material: Coal
Bench Height: 6.0 m
Stemming: 3.7 m
Burden: 7.0 m
Spacing: 7.0 m
Bore Diameter: 0.171 m
Explosives: ANFO
Challenge
Known as the land of a thousand rivers, South Kalimantan is one of Indonesia's rich and vast provinces, located in the central part of the archipelago. As home to numerous mines and a thriving industrial sector, the region is a crucial hub for mining operations.
Our client, based here, encountered hard rock formations in various parts of the mine. These proved difficult to fracture, especially at the top of the rock, resulting in poor fragmentation and longer excavation times, resulting in missed targets and overall productivity loss.
To address this, the on-site team initially adapted the blast design, from a 7x7x6m configuration with 45 kg of explosive per hole to a 7x7x7m configuration with 60 kg of explosive. While this adjustment yielded improved results, it was not the ideal choice due to persistent topside size and ejection issues, as well as increased vibrations that posed risks to surrounding buildings and communities. With the limitations on the number of charges per hole, improvements were necessary to limit the current vibrations.
Having collaborated on previous projects, MTi Group and PT. Prima Minechem Indonesia (MTi's local distributor) faced this challenge: solving a hard material problem without increasing drilling and blasting costs, while minimizing ejection and vibration. After a thorough assessment and several site visits, it became clear that a solution was needed to improve stemming efficiency—airdecking.
Solution
It was agreed that trials would be conducted to test the effectiveness of the air deck in increasing fragmentation size.
First, a proof-of-concept phase would be conducted, followed by an optimization phase to refine stemming efficiency and improve fragmentation. This will be tested with several blasts:
BLASTING 1 (POC): Split test (no deck vs. deck) with a 7m x 7m x 6m pattern
BLASTING 2 (POC): Split test (no deck vs. deck) with a 6m x 7m x 6m pattern
BLASTING 3 (Optimization): Full blast with a 6.5m x 8m x 6m pattern using an optimized blast design (faster excavation at lower costs).
To ensure objectivity, a set of KPIs was established considering four key elements:
- Excavation time – Target set at 10 seconds or less
- Powder factor – Target below 0.15 kg/Bcm
- Maximum explosive charge – 45 kgs
- Fragmentation target – Top layer size remains below 500 mm
Results
Overall, there was a significant improvement in the area where BLASTBAG was used in POC blasts (see graph above). There was an 8% reduction in P80 and a 21% reduction in XMAX when comparing BLASTBAG versus non-BLASTBAG blasts (reducing the dig rate by 21%).
From this point, they implemented an optimized blast design, resulting in stronger results. The average dig rate was 16% below current practice benchmarks (although slightly longer than POC 2). This equated to a significant increase in productivity with an 8% reduction in drilling and blasting costs (made possible by a lower Powder Factor and an optimized borehole depth from 6.0m to 7.0m, while maintaining a maximum explosive charge of 45kg).
Furthermore, the amount of rock was reduced, as seen in the blast footage, demonstrating the improved containment achieved with BLASTBAG. This was achieved by the air deck, which allows for reduced upward pressure on the dammed stemming.
Conclusion
By meeting all success criteria, the optimized blast design effectively resolved the challenging excavation issues and provided additional cost savings. The miner has been extremely pleased with the results and technical support received since adopting the air deck for all of their production blasting projects. With the challenges of challenging excavations eliminated, blasting vibration levels maintained, productivity has returned to optimal levels, enabling the efficient extraction of thousands of holes once again.
