Investigation of blast-induced rock fragmentation and fracture characteristics with different decoupled charge structures

Decoupled charge structure is widely employed in profile and production blasting of rock engineering, and its breakage effectiveness is closely linked to the utilization rate of explosion energy. In this investigation, the failure patterns and damage extent of cubic red sandstone specimens induced by blasting with various decoupled charge modes were examined through two groups of laboratory tests, and a three-parameter generalized extreme value (GEV) function was introduced to quantify the rock fragmentation size distribution (FSD) characteristics. Moreover, the Riedel-Hiermaier-Thoma (RHT) model parameters were calibrated based on the blasting test result of the R1 sample. Building upon this validated model, dynamic fracture behavior and pressure attenuation process in a dual-hole blasting finite element model with radial and axial decoupled charge structures were reproduced. Notably, the effects of delay time and initiation mode as well as coupling medium on the effectiveness of rock breakage were discussed. The results demonstrated that the three-parameter GEV function offers a more accurate characterization of the FSD features after rock blasting. Additionally, it is observed that the average fragment size decreases linearly with a reduction in the decoupling ratio, leading to a tendency for finer fragments and more uniform FSDs. Besides, through a comparative analysis of energy distribution characteristics and the volume of destruction in various coupling mediums for rock blasting, it is found that water, as a coupling medium, exhibits the highest energy transfer efficiency, followed by wet sand and dry sand, while air shows the least energy efficiency. Furthermore, the theoretical result of the stress transmission coefficient computed using the equivalent wave impedance method can proficiently reflect the extent of rock fragmentation in decoupled charge blasting.