The interaction mechanism of oppositely propagating cracks is an important basis for the study of rock fracture under dynamic loading. In this article, the stress field superposition and crack tip stress evolution are deeply investigated during the interaction of oppositely propagating cracks by using dynamic photoelastic experiment method and numerical simulation analysis. Obtained results indicate that the cracks interaction process is accompanied by the deflection of the crack, and the deflection of the cracks is mainly affected by the shear stress field at the crack tip. According to the difference of the crack deflection characteristics, the interaction process of the oppositely propagating cracks can be divided into two stages. The Stage I: the non-interlaced stage and Stage II: the interaction stage after the mutual staggered. It includes the period of Stage I that the oppositely propagating cracks are not interlaced with each other; the Stage II is the interaction period after the oppositely propagating cracks are interlaced with each other. The effects of stress intensity factor K_I, stress intensity factor K_II and far-field T stress on crack propagation process should be comprehensively considered when predicting the crack growth trajectory. The interaction of the stress field between cracks is the main factor determining the crack propagation trajectory. In addition, the vertical spacing between cracks also has a significant effect on the fracture behavior of oppositely propagating cracks. When the vertical distance between the two cracks is large, the local stress fields at the crack tip cannot overlap and interfere with each other, and the oppositely propagating cracks will expand independently of each other.

The dynamic fracture process of iron ore under blast loading is an important manifestation of ore fragmentation. To investigate the dynamic fracturing process of iron ore, Hopkinson bar experiments were conducted under different impact loads. The results indicate that under low strain rates, the dynamic stress–strain curve of iron ore exhibits compaction, elastic, and failure stages. However, as the strain rate increases, the compaction stage becomes less distinct, while the elastic modulus decreases and the failure strength increases, indicating the material toughness was enhanced at high strain rate. Moreover, under high strain rates, a significant increase in shear strain promotes the formation of tensile–shear cracks in the ore. In addition, based on the fragmentation of iron ore at different impact pressure, there exists a certain impact pressure, at which the proportion of large fragments decreases only slightly, while the amount of small fragments increases markedly. These findings provide important insights for optimizing fragmentation and improving blasting effectiveness.

To solve the problems of high explosive consumption, coarse fragmentation, and low energy utilization efficiency in open-pit blasting of layered rock masses, an axial staggered charging technology is proposed. The core idea of this new technology is to adjust the explosive structure according to the thickness of layered rock mass by setting ‘in-hole axial spacing charge and inter-hole staggering space’. By inserting air decks within boreholes and alternately offsetting the explosive sections between adjacent holes, the spatial distribution and timing of energy release are effectively regulated, leading to a more uniform stress field and improved utilization of explosive energy. An on-site field experiment was conducted at the western-262 region of the Yanshan Iron Mine. Both the rock fragmentation process, the vibration velocity and the distribution of rock fragment size were analyzed. The results show that, when compared with the ordinary continuous blasting technology, the axial staggered charging technique can effectively reduce the flyrock distance and produce a more compact muckpile, while peak vibration velocity is reduced by approximately 8.7% and explosive consumption is decreased from 0.19 kg/t to 0.17 kg/t, representing a decrease of about 10.5%. Moreover, the rock fragments exhibited a more uniform fragmentation size under the axial staggered charging technique, and the rock fragment size beyond 0.5 m decreased significantly. This study indicates that the axial staggered charging technology can reduce both the explosive consumption and rock fragments size in layered rock masses, providing a practical and technically feasible approach for optimizing deep-hole blasting design in such strata.