Influences of holes on dynamic propagation behaviors of blasting cracks

The influences of different spacings of holes on the pre-crack propagation behaviors of circular sand specimens under blasting loads are investigated. The explosive loading waveform from experiments is obtained as the loading stress of AUTODYN to simulate the crack propagation, and it is embedded in ABAQUS once more to calculate the stress intensity factor (SIF) of the static cracks under dynamic loads. The initiation-propagation time of pre-crack is measured by using CPG in the experiments. According to the CPG data to obtain the universal function, the dynamic initiation-propagation critical SIF is yielded by modifying the static SIF obtained from ABAQUS using the universal function. By comparing and analyzing the dynamic critical SIF, crack propagation velocity and length of crack propagation under different spacings of holes, we can obtain the following conclusions: (1) The holes have an effect on the dynamic propagation behaviors of cracks under blasting loads, and the smaller the spacing, the more remarkable the effect. (2) In general, the crack initiation critical SIF is higher than the propagation one, and the crack propagation velocity has influences on SIF, and their overall trends are inversely propotional. (3) The critical propagation SIF of cracks increases due to the action of the holes when they propagate near the holes, both of whose propagation length and velocity are reduced. In addition, if we take the holes as the auxiliary or surrounding ones in tunnel smooth blasting, the conclusions of this study will provide theoretical support for controlling the crack propagation length to achieve the integrity of surrounding rock.