Blast-induced fracture of rock plates with polygonal boreholes

To achieve controllable release of explosion energy in rock and to induce directional damage and fracture, this study investigates the dynamic fracture characteristics of rock plates containing polygonal boreholes under coupled charging conditions. Rock plates with regular triangular, square, regular hexagonal, and circular boreholes were used for blasting model experiments, and numerical simulations were carried out using our self-developed damage constitutive model. By comparing the near-field failure patterns and the spalling ring diameters in experimental and simulated results, the numerical simulations were verified. Based on this, the numerical damage variation reproduced the near-field failure processes, which were not observed in the experiments due to the escape of gaseous detonation products. The results show that the regular triangular and square boreholes induce more pronounced directional damage in the near-field, and the damage intensity along the borehole sides is stronger than that at the corners. Analysing the three-dimensional stress state near the borehole sides and corners in conjunction with the maximum shear stress criterion, it is found that stress superposition at the borehole corner weakens its directional damage capacity. Additionally, the nearly circular spalling rings formed in all specimens indicate that far-field fractures were not affected by the borehole shape. This phenomenon is consistent with the dynamic Saint-Venant's principle, which states that geometric singularities at the loading end have an effect within a limited range. These findings provide a basis for the future application of non-circular boreholes in mining blasting, particularly for borehole shape selection, directional design, and borehole spacing optimization.