Mechanism of iron ore blasting fracture using axial uncoupled charges

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.