Stress wave superposition effect and crack initiation mechanism between two adjacent boreholes

In rock blasting, the effect that stress wave superposition between boreholes has on rock fragmentation remains controversial. Here, we experimentally study the stress wave superposition effect between two adjacent boreholes by combining the model experiment method and the high-speed digital image correlation experimental system. Numerical simulations based on the continuous-discontinuous element method are also used to analyze the crack initiation mechanism between two adjacent boreholes. The model experiment results show that, in the stress wave superposition area between boreholes, the stress component in the direction of the connection line of the two boreholes is mainly compressive, while that in the direction perpendicular to the connection line is mainly tensile. Superposition of the blasting stress waves between the boreholes strengthens both stress components, but the strengthening effect on the stress component in the direction perpendicular to the connection line (mainly tensile) is significantly less than that in the direction of the connection line (mainly compressive). Moreover, these stress enhancements are not sufficient to induce crack initiation in the stress wave superposition area between boreholes. Numerical simulation analysis further shows that crack initiation in the stress wave superposition area has relatively stringent requirements on the explosive parameters, rock properties and borehole spacing, which are difficult to observe in engineering practice and model experiments