Influence of filled joints with different inclination angles on rock blasting fragmentation

The presence of joints significantly influences the performance of rock blasting. The impact of different joint inclination on blasting fragmentation was studied through a combination of experiments and numerical simulations. In this study, a group of concrete model specimens containing joints with different angles was used to carry out blasting experiments to investigate the effect of joint inclination on blast fragmentation. During experiments, detonators were placed in vertical boreholes in the specimens and detonated, while high-speed camera was used to capture the fragmentation process. The dynamic responses of joint surfaces at different time intervals after detonation was observed, and blasting fragmentation distribution was extracted using image processing techniques. The effect of joint inclination on blasting fragmentation was analyzed. Then LS-DYNA finite element numerical simulations were developed to obtain the propagation of stress waves and the evolution of strain fields within the specimens. Experimental and numerical results indicated that the joints have a significant influence on the distribution of blasting fragmentation and the propagation of stress waves, and the impact of the joints on the blasting performance was mainly attributed to the reflection of blasting waves from the joints, which was related to the deformation characteristics of the joints. With the increase of joint inclination, the blasting fragmentation initially decreased followed by an increase. The effective stress and peak particle velocity (PPV) transmission in the joints decreased overall with the increase of joint inclination but showed a rebound between 45° and 60°, which identified approximately 45° as the most favorable condition for rock fragmentation under blasting. Moreover, the results obtained from numerical crack network reconstruction and image processing revealed that there was an upsurge in the occurrence of vertical cracks in the specimen as the joint inclination increased, while a decline was observed in the presence of horizontal cracks. These study results help in understanding the interaction between joints and blasting stresses and optimizing blasting parameters in jointed rock.