Numerical study on the influence of various external factors on the blasting of rock masses in crushing and fracture zones

This study aims to systematically investigate the coupling effects of in situ stress, joints and free surfaces on rock blasting damage. By determining tuff-specific Riedel‒Hiermaier‒Thoma (RHT) constitutive parameters via split Hopkinson pressure bar (SHPB) tests and employing a smoothed particle hydrodynamics–finite element method (SPH-FEM) model in LS-DYNA, it reveals how these factors collectively control damage zone distribution, crack propagation and ejection behavior. The findings provide a theoretical basis for optimizing blasting design in high in situ stress and jointed rock masses. This research employs an integrated methodology: First, tuff-specific RHT constitutive parameters were determined via SHPB tests and theoretical calibration. Subsequently, a 3D blasting model was developed using the SPH-FEM coupled approach on the LS-DYNA platform. This model systematically simulated the individual and coupled effects of in situ stress, joints and free surfaces. The approach combined experimental parameter determination with advanced numerical modeling to quantitatively analyze damage mechanisms and ejection behavior. This study reveals that in situ stress type dictates blasting damage patterns: hydrostatic fields suppress cracks but enhance crushing, while non-hydrostatic fields cause directional damage. Joints create asymmetric cracks and energy concentration, interacting with in situ stress to expand the crushing zone. Free surfaces control crushing scale via wave reflection, dynamically interacting with in situ stress redistribution. Parameter sensitivity analysis identifies Fs* as most critical for stress and damage. These findings provide mechanisms for precise blasting control in complex geological conditions. (1) Simplified representation of complex joint networks and rock heterogeneity in the model. (2) Assumed linear elastic behavior for intact rock segments prior to failure. Based on the findings, this study proposes targeted blasting strategies: For hydrostatic stress fields, increase charge to overcome confinement; for non-hydrostatic fields, align the minimum resistance line with the maximum principal stress. Implement stress relief holes and directional blasting in jointed rock masses. Apply millisecond initiation to optimize the “free surface-stress-energy” mechanism. These approaches enable precise control of damage and ejection trajectories, providing practical guidance for tunnel blasting in high-stress strata, jointed rock masses and multi-free surface conditions. This research enhances blasting safety and efficiency in underground construction and mining, directly benefiting infrastructure development and resource extraction. By enabling precise damage control, it reduces geological hazards, minimizes support costs and improves operational safety for personnel. The optimized techniques contribute to more sustainable rock excavation by lowering energy consumption and environmental disturbance. Ultimately, the study supports safer, more economical and more environmentally responsible engineering practices in geotechnically complex projects. This study's originality lies in systematically revealing the coupling mechanisms of in situ stress, joints and free surfaces on rock blasting. It provides novel insights into their synergistic control over damage distribution and ejection behavior. The value is demonstrated through determining tuff-specific RHT parameters and establishing a reliable SPH-FEM model. These findings enable precise blasting control in complex geology, offering practical strategies for optimized design in tunneling and mining, ultimately advancing both theoretical understanding and engineering practice in rock blasting mechanics.