Dynamic evolution mechanism of cracks in eccentric decoupled charge blasting under high in-situ stress in rock mass

As a core technology for deep rock mass excavation, the blasting performance of the drilling-and-blasting method is profoundly governed by the coupling effect between charge configuration and in-situ stress fields. However, existing literature has not fully elucidated the mechanism of eccentric decoupled charge (EDC) induced by gravitational forces during field charging operations, nor its coupling dynamics with in-situ stresses. This study first establishes a theoretical model of the coupled stress field through mechanistic analysis to decode the stress superposition principle. Laboratory single-hole blasting experiments are then conducted to validate the numerical model and calibration parameters. Using numerical simulations, crack propagation patterns are systematically investigated under both stress-free and in-situ stress conditions. Hough transform-based image processing techniques are employed to quantitatively analyze the influence of the radial decoupling coefficient (M) on blasting crack distributions in stress-free environments. Fractal dimension theory and fractal damage mechanics are integrated to characterize crack propagation in isotropic/anisotropic stress fields and quantify stress-induced rock damage. Results indicate that the frequency of crack initiation on the coupled side exceeds that on the decoupled side by 5.67%–36.82%. In-situ stress exerts bidirectional control over crack evolution: the maximum principal stress dictates the direction of crack extension while reducing fractal damage by 9.3%–12.5%. Notably, EDC significantly alters dynamic stress evolution, with the peak disparity between tensile and compressive hoop stresses identified as the critical factor driving divergent crack patterns. The research findings clarify the coupling mechanism between EDC and in-situ stress. When applied to blasting engineering in deep surrounding rock, this mechanism can significantly improve the semi-perforation rate and reduce overbreak. The study provides a theoretical basis and technical support for smooth blasting in deep surrounding rock engineering.