Directional fracture behavior and stress evolution process of the multi-slit charge blasting

The multi-slit charge developed from the traditional double-slit charge has more and more engineering applications in roadway blasting and excavation. In this paper, numerical simulation and model experiments are used to compare the dynamic behaviors of double-slit/three-slit charge blasting in crack propagation, stress evolution and blasting vibration. The research results show that the directional fracture effect at the borehole middle and borehole bottom in the slit charge blasting is the best, followed by the directional fracture effect at the borehole orifice, and the length of the directional crack formed along the slit direction at the borehole middle is the largest. Compared with the double-slit charge blasting, the dynamic stress intensity factor of the directional crack at initiation stage and early propagation stage in the three-slit charge blasting is smaller, and the directional cracks formed are shorter. In addition, the effective stress evolution and blasting vibration attenuation of the gauging points along the slit direction are affected by slit number and cross-section position. The effective stress and blasting vibration of gauging points at the borehole bottom in the slit charge blasting are significantly larger than those of gauging points at the borehole orifice. For the three-slit charge blasting, the model experiment finds that the directional crack deflected to the side of protected rock mass during the propagation process. The occurrence of such deflection phenomenon is likely to cause overbreak of rock mass, which is not conducive to the formation of a straight profile surface in the rock roadway excavation.