Profile
Material: Coal
Bench Height: 6.7 m
Initial Stemming: 4.3 m
Burden: 8.0 m
Spacing: 9.0 m
Bore Diameter: 0.200 m
Optimization Method: Water
Krakatau BLASTBAG™ Decking
Challenge
Efficiency at Risk of Hampering Productivity
Before using the air decking method, one of our clients implemented a blasting design with an 8 x 9 m geometry and a PF of 0.14 kg/bcm. Commodity price pressures prompted cost-efficiency efforts in explosives consumption. A 5 kg reduction per hole was implemented in the hope of reducing costs without compromising performance. However, this reduction effort actually resulted in hard digging, a condition where hard material is difficult to excavate, resulting in:
- Decreased productivity.
- Failure to achieve KPI targets for excavation time.
- Suboptimal fragmentation.
These issues significantly hampered productivity in the mining area, despite the targets being achieved, as shown in the attached table. The KPI targets set by our client were:
| PARAMETER | TARGET |
|---|---|
| DIGGING TIME | 9 Second |
| PF | 0.13 - 0.12 kg/bcm |
| FRAGMENTASI | < 500 mm |
This situation highlights the need for a solution that can reduce Powder Factor (PF) without compromising productivity and fragmentation performance.
How can we reduce PF without inducing hard digging, while still meeting fragmentation and productivity KPIs?
Solution
Optimizing Energy, Not Just Reducing Explosives
To address these challenges, blasting was conducted based on energy distribution optimization, while maintaining the existing geometry to allow objective comparison of results. BLASTBAG™ Krakatau was used as an air-decking tool, positioned on the top air deck, replacing some of the stemming material.
This approach aimed to:
- Avoid over-confinement, which could potentially trigger excessive vibration
- Create an air gap for more even energy distribution
- Maintain stable energy confinement with the stemming material
The blasting design changes resulting from the use of BLASTBAG™ Krakatau are shown in the table below.
| PARAMETER | BEFORE MODIFICATION | AFTER MODIFICATION |
|---|---|---|
| STEMMING | 4.3 Meter | 3.8 + 1.0 (Airdeck / BLASTBAG) |
| CHARGE LENGTH | 2.7 Meter | 2.3 Meter |
| POWDER FACTOR | 0.14 (kg/bcm) | 0.12 (kg/bcm) |
Results
Powder Factor Efficiency, Optimal Digging Time, and Fragmentation Achieved KPI Results
- Powder Factor Reduction
The use of BLASTBAG™ Krakatau successfully reduced powder factor by 7–14%, from 0.14 to 0.12 kg/bcm, without compromising blasting performance (see the graph below). - Digging Time Achieved KPI Results
- The average digging time was 8.7–8.9 seconds, meeting the KPI target of 9 seconds.
- There were no hard material issues in all three blasting sessions.
- Average Blast Recovery reached 92% (close to full recovery).
- Fragmentation Remains Optimal
Fragmentation Parameters (see the graph below):-
- Avg D80 256 mm
- Avg Xmax 439 mm
- Avg Passing <500 mm 99%
This demonstrates that reducing powder factor does not reduce fragmentation quality (see the graph below).
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Conclusion
The implementation of Krakatau's Air-Decking BLASTBAG™ at our client's site delivered significant results in blasting cost efficiency without sacrificing blast quality or productivity:
- Reduced PF by up to 14%
- Maintained digging time within KPIs without hard digging
- Fragmentation remained within target limits (<500 mm)
- Improved safety by reducing the risk of vibration and over-confinement
