Key Takeaways & Executive Findings
- •• • Layered in-hole charge increased rock fragment horizontal velocity from 2.0 m·s⁻¹ (continuous) to 7.0 m·s⁻¹, indicating more efficient energy transfer to the upper bench section, which is critical for reducing oversized boulders in production blasting. • • Maximum block size in the top specimen section dropped from 9.0 cm (continuous) to below 5.0 cm (layered), directly addressing the common problem of oversized rocks in the upper part of bench blasts, thereby reducing downstream crushing costs. • • DEM-PBM simulations closely matched experiments, predicting a maximum block size of 8.8 cm for continuous and <5.0 cm for layered charge, with velocity of 6.8 m·s⁻¹, validating the numerical model as a reliable tool for blast design optimization. • • Field-scale application in open-pit coal mine overburden reduced boulder yield from 48.1% to 5.6%, demonstrating that layered charge can dramatically improve fragmentation efficiency and operational productivity in real-world deep-hole blasting.
Abstract
To improve rock fragmentation in open-pit deep-hole blasting, an in-hole layered column charge configuration was designed. Small-scale blasting tests on sandstone specimens were conducted under continuous and layered column charges to capture the failure process and final fragmentation. DEM-PBM coupled simulations visualized the dynamic fracture evolution and validated the experimental observations. Results show that under continuous charge, the top quarter of the specimen developed only a single blast-induced crack, splitting it into two parts, with horizontal fragment velocity of 2.0 m·s⁻¹ and a maximum block size of 9.0 cm. In contrast, layered charge produced multiple cracks in the top quarter, fragmenting it into smaller pieces, increasing horizontal velocity to 7.0 m·s⁻¹, and eliminating blocks larger than 5.0 cm. Simulations confirmed these trends, with maximum block size reduced from 8.8 cm to below 5.0 cm and velocity reaching 6.8 m·s⁻¹, closely matching experiments. Field trials in an open-pit coal mine overburden blasting demonstrated that layered charge reduced the boulder yield from 48.1% to 5.6%, significantly improving fragmentation. The findings confirm the practical effectiveness of in-hole layered column charge in enhancing rock breakage in deep-hole bench blasting.
1. Introduction
Conventional deep-hole bench blasting in open-pit mines relies on continuous column charges, which concentrate explosive energy near the bottom of the blast hole. This often leaves the upper, uncharged section of the bench inadequately fractured, producing oversized boulders that require secondary blasting or mechanical breaking, thereby increasing operational costs and delays. The challenge is particularly acute in overburden removal where rock mass is often massive and jointing is sparse.
To address this bottleneck, the present study introduces an in-hole layered column charge design that distributes explosive energy along the hole axis in discrete segments. By creating multiple initiation points, the design aims to enhance crack propagation in the upper rock column, improving fragmentation uniformity. This paper systematically evaluates the technique through small-scale blasting tests, DEM-PBM simulations, and field trials, providing quantitative evidence of its effectiveness in reducing boulder yield and improving overall blast performance.
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CHENG Bing, YE Fu, WANG Quan, CHENG Yangfan, ZONG Qi, XU Ying, WANG Mengxiang, LI Junhao (2026). Blasting Failure Characteristics of Rock Specimens under In-Hole Layered Column Charge. Chinese Journal of Energetic Materials (含能材料). https://doi.org/10.11943/CJEM2026001
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Frequently Asked Questions
What is the mechanism by which layered charge improves fragmentation in the upper part of the blast hole compared to continuous charge?
Layered charge creates multiple explosion sources along the hole, generating stress waves that interact and reflect more effectively with the free surface and existing cracks, leading to multiple crack initiation and propagation in the upper rock section. This results in a higher horizontal fragment velocity (7.0 m·s⁻¹ vs. 2.0 m·s⁻¹) and smaller maximum block size (<5.0 cm vs. 9.0 cm) as observed in experiments.
How does the DEM-PBM simulation compare with experimental results in terms of predicting fragment size and velocity?
The DEM-PBM simulation predicted a maximum block size of 8.8 cm for continuous charge and <5.0 cm for layered charge, closely matching experimental values of 9.0 cm and <5.0 cm, respectively. The simulated horizontal velocity for layered charge was 6.8 m·s⁻¹, which is within 3% of the experimental value of 7.0 m·s⁻¹, confirming the model's accuracy.
What are the practical implications of reducing boulder yield from 48.1% to 5.6% in terms of operational efficiency and cost?
Reducing boulder yield from 48.1% to 5.6% significantly decreases the need for secondary blasting or mechanical breaking, which are time-consuming and costly. This improvement can lead to substantial savings in drilling, explosives, and equipment wear, as well as increased productivity in the mining cycle.
Are there any limitations or potential issues with implementing layered charge in production blasting, such as increased complexity or cost?
Layered charge requires more careful loading procedures and possibly specialized equipment to place multiple explosive decks with stemming between them. This may increase loading time and labor costs. However, the significant improvement in fragmentation and reduction in boulder yield likely outweigh these additional costs, as evidenced by the field trial success.
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