Key Takeaways & Executive Findings
- •• Continuous charging yields the most extensive rock damage, while an axial uncoupling coefficient of 1.50 results in the least damage. • Moderate air deck lengths enhance blasting effectiveness and rock fragmentation, but increasing air deck length reduces explosion shock wave peak pressure by 37.8% to 66.3%. • Advanced 3D reconstruction and fractal analysis enable quantitative assessment of fracture networks and damage extent in blasted rock. • LS-DYNA numerical simulations accurately predict cumulative rock damage, validating laboratory findings and supporting practical design optimization.
Abstract
The axial uncoupling coefficient and air deck effect in blasting significantly influence the effectiveness of rock fragmentation. This study employs a passive confinement device to conduct continuous charge and five different axial uncoupling coefficient blasting experiments on cylindrical iron ore samples to explain the rock-breaking mechanisms associated with various axial uncoupling coefficients and air deck effects. It utilizes advanced techniques such as computer tomography (CT) scanning, deep learning, and three dimensional (3D) model reconstruction, to generate a 3D reconstruction model of “rock explosion cracks” under varying axial uncoupling coefficients. This model illustrates the spatial distribution and configurations of explosion cracks. Integrating box-counting dimension and fractal dimension theories enables the quantitative analysis of the three-dimensional fracture field and the extent of damage in rocks subjected to explosive forces. Laboratory 3D experimental results indicate that continuous charging produces the most extensive damage, while a uncoupling coefficient of 1.50 (case 1) results in the least. A moderate air deck length enhances blasting effectiveness and rock fragmentation. For identical charge quantities. In contrast, increasing the charge amount with a constant air deck length further augments rock fragmentation. A rock blasting calculation model was developed using LS-DYNA numerical simulation software under various axial uncoupling coefficients. This model depicts the dynamic damage evolution characteristics of the rocks and variations in hole wall pressure. The numerical simulation results of cumulative rock damage align with the laboratory findings. In addition, increasing the air deck length reduces the peak of the explosion shock wave, decreasing the peak pressure in the charge and air sections by 37.8% to 66.3%. These research outcomes provide valuable theoretical support for designing and optimizing axial uncoupling coefficients in practical applications.
1. Introduction
Due to their economic efficiency and effectiveness, drilling and blasting are widely utilized in excavating engineering rock for transportation, water conservancy, hydropower, underground mines, and other construction projects. This technology harnesses the energy produced during an explosion to deform, fracture, displace, and eject the blasted material [1–4]. Air uncoupled charging structures are frequently employed in tunnel smooth blasting and open-pit presplitting blasting. The radial air uncoupled charging structure can mitigate the peak of the explosion shock wave and reduce the pressure peak, minimizing the crushing zone near the borehole and effectively improving the energy utilization rate of explosives. In contrast, the axial uncoupled charge structure can extend the duration of the explosive gas’s effects, distributing the explosive stress field uniformly along the entire borehole length, thus enhancing rock fragmentation. Therefore, studying uncoupling charge structure blasting is essential for enhancing the energy utilization rate of blasting and achieving optimal blasting effects.
Numerous blasting engineers and rock dynamics researchers have conducted extensive theoretical analyses, laboratory experiments, and numerical simulations to understand the mechanism of rock blasting under air uncoupled charge structures [5]. The initial pressure exerted on the borehole wall during rock blasting is pivotal in rock fragmentation. Utilizing the isentropic and adiabatic expansion models, Chen et al. [6] determined that in uncoupled charge blasting, the increase in borehole wall pressure following the blast shock wave’s impact collides with the borehole wall is related to the type of explosive and the radial uncoupling coefficient. The peak pressure on the borehole wall from the axial uncoupling charge structure is approximately proportional to the axial uncoupling coefficient. As the uncoupling coefficient increases, the crushing area near the borehole diminishes, and the interaction between explosive-induced cracks leads to effective rock fragmentation. Thus, the uncoupling coefficient significantly affects the size and distribution of blasting rock fragments [7–8]. Dynamic caustics explosion loading experiments and digital image correlation testing methods are employed to capture the intrinsic mechanism of rock breaking under explosion loads. These methods measure the dynamic propagation and interaction of cracks, and the physical characteristics of cracks, under an uncoupled charge structure [9–11]. They also visualize the evolution and ...
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Yuanyuan You, Renshu Yang, Jinjing Zuo, Zhen Yang, Jin Li, Yong Zhao, Haibao Yi (2025). Mechanism of iron ore blasting fracture using axial uncoupled charges. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3038-x
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Frequently Asked Questions
What is the axial uncoupling coefficient in blasting?
The axial uncoupling coefficient is the ratio of the borehole diameter to the charge diameter in the axial direction. It influences the distribution of explosive energy and the effectiveness of rock fragmentation.
How does the air deck length affect blasting results?
A moderate air deck length enhances blasting effectiveness by allowing explosive gases to act over a longer duration and distribute stress more uniformly. However, increasing air deck length reduces the peak pressure of the explosion shock wave, which can decrease fragmentation efficiency.
What methods were used to analyze rock damage in this study?
The study used CT scanning, deep learning, 3D model reconstruction, and fractal dimension analysis (box-counting dimension) to quantitatively assess the three-dimensional fracture field and damage extent in blasted rock samples.
What is the practical significance of this research?
The findings provide theoretical support for designing and optimizing axial uncoupling coefficients in practical blasting operations, helping to improve energy utilization and achieve better rock fragmentation.
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