Insight into Rock Fragmentation and Damage Affected by Temporal Characteristics of Blast Loading

Focussing on the effect of the temporal characteristics of blast loading on rock fragmentation and damage, a self-developed constitutive model considering equivalent stress history is adopted for numerical simulation studies. Fitting and statistics of published test data on rock dynamic strength indicate that the incubation characteristic time that reflects the dynamic sensitivity of rock strength is distributed in the range of 10 ~ 110 μs. For the single-hole loading model, as the incubation characteristic time increases, the average damage value of rock elements decreases in a power law, which indicates that the increased dynamic sensitivity of rock strength is unfavourable for blasting damage. However, a short rise time of blasthole pressure corresponds to a high loading rate that encourages the rock at a high dynamic strength, which favours more explosive energy transmitted through the crushed zone and promotes cumulative damage to the mid- and far-field rock. The spalling crack width and maximum radial crack length at the typical moment show an “N”-shaped trend with the incubation characteristic time. This results from the asynchrony between the two effects of promoting the explosion energy transmitted through the crushed zone and suppressing the dynamic damage in the mid- and far-field rock, when the incubation characteristic time (dynamic sensitivity of rock strength) is increased. For the multi-hole loading model with a delay time ≤ 800 μs, the fitting and statistical result of the median fragment sizes show a dispersion with no obvious trends. However, the average damage value of rock elements is affected by short delay time in an approximately “N”-shaped trend. This suggests that the average damage value seems to be more suitable for evaluating the effect of delay time on blasting result than fragment size distribution. Therefore, for both field and laboratory blasting experiments, we suggest that the energy consumption of post-blast fragment crushing and grinding can be attempted as an indicator for selecting the optimal short delay time.