Blast-induced fracture mechanisms and fragmentation characteristics of brittle materials under anisotropic stress fields

In deep rock blasting excavation, in-situ stress significantly influences the fragmentation effect. Even at the same burial depth, complex tectonic movements result in uneven horizontal stress fields, subjecting the rock being excavated to anisotropic stress conditions. In this study, blasting tests are conducted with various lateral pressure coefficients, using a self-designed experimental system. A point-cloud–based method for three-dimensional (3D) blast-crater reconstruction and parameter calculation is proposed, facilitating visual modeling of craters and precise volume measurement. 3D numerical models are established to investigate the damage-zone evolution and stress distribution during the failure process of concrete. Finally, field blasting tests are conducted in an underground mine. The experimental results show that the optimized triangulated irregular network and contour models effectively depict the 3D morphological characteristics of the blast crater, with the combined crater from double-borehole blasting exhibiting a double-cone flattened shape. With the increase in the disparity between the horizontal and vertical stresses, the area, diameter, and volume of the crater, as well as fragment size and number, decrease, whereas the opening angle gradually increases. The numerical results indicate that there exists a threshold value for the lateral pressure coefficient (0.5< γ < 0.8) at which the resulting single-sided crater becomes circular. The parameters and morphology of blast craters are determined by the flaky failure zones, which are significantly influenced by static stresses. Short delays alter the blasting effect of the later-detonated borehole, inhibiting the formation of circumferential cracks and promoting the propagation of radial cracks. Field-test results indicate that an increase in the horizontal stress leads to a significant rise in the quantity of large-sized fragments generated by blasting, validating the reliability of the model tests and numerical simulations.