Numerical study on rock blasting assisted by in-situ stress redistribution

Abstract

During tunnel blasting at deep depths, the rock mass is frequently subjected to high in-situ stress. Except for explosive detonation, the in-situ stress itself, particularly the stress concentration due to stress redistribution, also possesses the potential to cause rock fracture. Then there is a possibility of utilizing the stress redistribution to assist rock fragmentation during blasting. However, this concept has not garnered sufficient attention and systematic research in the field of tunnel blasting. The present study numerically investigated the rock fracture resulting from blasting with assistance of stress redistribution under various in-situ stress conditions with a focus on the full-face blasting of a deep circular tunnel. Based on the numerical modeling, the blasting parameter change required to maximize the auxiliary effect of in-situ stress redistribution was discussed. The results show that blasting of the previous round of blastholes creates a temporary cavity that induces in-situ stress redistribution. The redistributed stress generates cracks in the rock mass assigned to blasting of the current round of blastholes, particularly under high and anisotropic in-situ stress as well as large cavity conditions. The presence of these pre-generated cracks, together with their enhanced reflection of explosion stress waves, contributes to an increase in the degree of rock fragmentation during blasting. By utilizing the auxiliary effect of in-situ stress redistribution, there is a significant reduction in the amount of explosive required, with a saving of up to 30% demonstrated in the used computation example. The assistance of in-situ stress redistribution on rock blasting is particularly pronounced in the rock mass aligned along the orientation of minor principal stress and with larger cavities. As a result, increasing the blasthole burden in the orientation of minor principal stress and equipping the blastholes in the outer rounds with a larger burden contribute to maximize the auxiliary contribution of in-situ stress redistribution and expand the scope of rock fragmentation during blasting.