Effect of joint dip angle and inter-hole parameters on blasting crack propagation in layered rock mass

In the construction process of drilling and blasting method for layered rock tunnel, the unbalanced distribution of explosion energy was easy to cause serious over- and under-excavation. The joint dip angle, inter-hole delay, and hole spacing were the main influencing parameters. The simulated rock mass samples with different joint dip angles were prepared by the layered pouring method, and the blasting test of layered rock mass was carried out. Based on the ABAQUS simulation software, the blasting crack propagation and stress wave propagation characteristics of layered rock mass under different joint dip angles were analyzed. The results show that the joint dip angle has a significant guiding effect on the stress wave propagation. By affecting the stress distribution, the peak strain and damage degree at different positions are different, which in turn promotes the crack propagation at the joint surface or around the blast hole. The inter-hole delay plays a key role in regulating the crack propagation path. With the increase of delay time, the stress wave superposition area of the pre-blasting hole and the post-blasting hole gradually shifts from the joint center to the surrounding of the post-blasting hole, resulting in the peak strain and damage value of the joint center increasing first and then decreasing, and the failure area of the rock mass shifts to the post-blasting hole accordingly. However, too long delay weakens the synergistic effect of the double-hole stress wave. The increase of hole spacing weakens the stress superposition in the center of the joint, so that the energy is concentrated around the borehole, and the crack propagation mode changes from joint penetration to radial distribution around the borehole. However, too large a hole spacing is easy to lead to the failure of crack penetration between holes due to insufficient energy attenuation and stress superposition, which significantly reduces the crushing efficiency of rock mass. The research results are helpful to the understanding of blasting crack propagation in layered rock mass.