Analysis of the directional fracture capability of slotted cartridges at various slot angles and their practical applications

This study systematically investigated the influence of slot angle on the directional fracture capability and slotting effect of slotted cartridges. Initially, Two-dimensional dynamic caustic experiments were utilized to assess the dynamic behavior of blast-induced cracks under various a configurations. 3D PMMA column model experiments and CT scans were conducted to characterize blasting-induced cracks and assess the directional fracture capability of slotted cartridges. The laboratory findings were validated through field tests. The results indicated that different a could consistently produce directional cracks, and the longest secondary crack was longer when a was below 180°. The magnitude of superimposed stress waves generated during the propagation of the two primary cracks determined the length of the longest secondary crack, while the size of stress waves altered the angle between the longest secondary crack and the primary cracks. The a is inversely proportional to the damage in the non-slot regions. The 3D PMMA column model experiments further validated the findings from the 2D dynamic caustic experiments. An increased a resulted in gradual decreases in the fractal dimension, damage value, and surface area of cracks. Field tests demonstrated that selecting slot angles that match the profile can effectively control over-excavation and under-excavation, thereby substantially improving blast hole utilization efficiency.