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, often leading to issues such as over or under excavation in deep rock masses. In this paper, a theoretical model for presplit blasting under in-situ stress in rock engineering was developed based on the assumption of plane-strain problem of elastic mechanics. The propagation and attenuation of explosion stress waves were analyzed using a combination of Laplace transforms and numerical inversion. Furthermore, the impact of initial static stress on the blasting-induced dynamic stress field distribution in presplitting was examined and discussed. The Riedel-Hiermaier-Thoma (RHT) model in LS-DYNA code was employed to investigate the dynamic mechanical behavior of rock mass, and its material parameters were calibrated by comparing blasting crack patterns and the explosion pressure attenuation curves. Then, the validated model was used to simulate the damage features of rock presplit blasting under both hydrostatic and anisotropy pressure conditions, thereby analyzing the effects of the static stress and the dynamic pressure on the crack extension behavior. In addition, the distribution characteristics of blasting cracks are quantitatively characterized by the Hough transform method. The results indicate that the difficulty in crack coalescence for deep rock presplit blasting is primarily attributed to the reduction of tangential tensile stress caused by the in-situ stress. This prevents the formation of tensile fracture planes between boreholes due to restricted tangential displacements, which was demonstrated by the evolution of circumferential tensile stress and particle displacement vectors. Moreover, a crack coalescence criterion in presplit blasting was proposed to predict whether inter-borehole cracks penetrate based on the damage theory of stress wave superposition, 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.