Effect of in-situ stress on fracture formation process of rock mass in presplit blasting

The evolution and distribution characteristics of cracks in presplit blasting can be significantly affected by the in-situ stress, leading to problems such as over/under excavation in deep rock masses. In this investigation, a theoretical model for rock presplit blasting under initial stress was developed based on elastic mechanics. The propagation and attenuation process of explosion stress waves were analyzed by the combination of Laplace transforms and numerical inversion. Then, the influence of initial static stress on the blasting dynamic stress field distribution in presplitting was analyzed. In addition, the explicit dynamic numerical approach was employed to simulate the failure process in presplit blasting under both hydrostatic pressure and anisotropy pressure conditions, and the effects of static and dynamic stresses on cracking behavior and pressure evolution are reproduced and discussed. Moreover, the distribution characteristics of blasting cracks are quantitatively characterized by the Hough transform method. The results showed that the crack coalescence difficulty in deep rock presplitting is primarily attributed to the reduction of tangential tensile stress induced by the in-situ stress. The rock particles between boreholes fail to form tensile fracture planes due to restricted tangential displacements, which was demonstrated by the evolution of circumferential tensile stress and particle displacement vectors. Furthermore, the crack coalescence criterion in presplit blasting was proposed to predict whether inter-borehole cracks penetrate based on the theory of stress wave interference damage, and the relationship between charge diameter and hole spacing under various in-situ stress can guide the arrangement of boreholes, thus improving the presplit blasting effectiveness for deep rock masses.