The Effect of Stress Wave Interaction and Delay Timing on Blast-Induced Rock Damage and Fragmentation

Rock fragmentation by blasting is the most efficient way of rock breakage in hard rock mining applications. Fragmentation, as well as the properties of the fragments generated by the explosion, are of significant concern as the energy consumption at the mill is greatly affected by them. Dynamic loading of blasting generates a countless number of microcracks in the host rock, which despite the major cracks forming the fragments could not get enough time to coalesce and create macrocracks. These microstructures eventually impact the integrity of the intact rock and reduce its strength. Damage is considered as a scalar parameter, which accounts for the creation of flaws and microstructures in the rock, deteriorating its elasticity modulus. The stress waves and their interactions are the parameters that control damage around blastholes. In this study, using LS-DYNA numerical code, the effect of initiation timing on blast-induced rock damage and fragmentation is investigated. The results of the numerical models reveal the importance of the delays in damage as well as fragment size distribution. Delayed initiation provides enough timing for the cracks to grow, which preconditions the surrounding rock for the neighboring blasthole. The interaction between the stress waves resulting from the detonation of neighboring blastholes plays an important role in damage and fragmentation analysis. The optimum delay time can be obtained by considering the rise time and the duration of the stress pulse, the P and S wave travel times in the host rock, and the crack propagation time within the rock burden.