Influence of the applied pressure waveform on the dynamic fracture processes in rock

Dynamic fracture process analyses for different waveforms of borehole pressure are conducted using a proposed numerical simulation method in order to verify the dynamic fracture mechanism related to blast-induced borehole breakdown. The fracture processes are affected more by the rise time increases than by the decay time. A higher stress-loading rate increases the number of radial cracks and leads to intense stress release around running cracks. The stress release caused by adjacent cracks interferes with crack extension and results in shorter crack propagation. At lower stress-loading rates, the number of cracks and the crack arrest caused by the stress released at adjacent cracks are reduced, leading to longer crack extension. These analyses reveal that the earlier preferential crack development occurs the greater the extension of the crack. The dynamic fracture process analyses are extended to investigate the influence of the waveform of applied pressure on the dynamic fracture process in a free face model. These fracture processes reveal that crack extension increases with the rise time increase, and that when the rise time is sufficiently long, crack extension depends, predominantly, on the rise time and the peak value of applied pressure. Crack arrest occurs after the peak phase of the stress wave in all cases. The effects of rock inhomogeneity on fracture pattern are discussed. (C) 2004 Elsevier Ltd. All rights reserved.