Numerical study on blasting crack propagation and coalescence in granite rock

Blasting-induced crack networks considerably impact the extent of rock fragmentation and the evaluative construction qualities of deep underground facilities. Based on the Hoek-Brown criterion, an integrated strategy of the Johnson-Holmquist (JH-2) model, failure criterion, and crack softening failure model was used to numerically explore the influences of borehole distance, time interval, and confining pressure on blasting crack propagation and coalescence. First, one-borehole blasting was used to reproduce the crack propagation results under free and non-reflecting boundaries, and the good results provided compelling evidence of the reliability of this strategy. For the two- and three-borehole blasting, it was discovered that high confining pressure paired with the large time interval was not favorable for crack coalescence. Therefore, simultaneous initiation is an optimal plan, which is not dependent on time interval and confining pressure. Simultaneously, if the borehole distance remains unvaried, the predominant influence on crack coalescence transitions from the time interval to the confining pressure as these two factors increase. Moreover, crack coalescence takes place when the tensile stress field of one crack is not converted into the compressive stress field of another crack, and crack coalescence has two key mechanisms: mutual and indirect modes. In addition, the dependence of controlling parameter on coalescence mode has been discussed.