Dynamic strength and fragmentation of selected rocks under impact loading

Understanding the fracture process in rock under high strain rate loading is essential to quantifying the blasting process and predicting the degree offragmentation in rock blasting. However, compared to our knowledge base on the detonation properties of commercial explosives, the properties of rock that control the fracture process are relatively poorly known. In this study, a set of twelve rock types covering a wide range in mineralogy, texture and homogeneity were investigated for their compressive strength under high strain rate loading. The corresponding static compressive strengths were also measure in the same rock types and in identical dimensions tor comparison. The resulting fragments after each test were analysed for size distribution. A Split Hopkinson Bar apparatus was used to generate the required high strain rate loading. The dynamic compressive strength at a strain rate of 10³ Isec was found to range between 2.5 and 4.6 times the corresponding static strength. The resulting particle size distribution under dynamic fracture process was also found to be much smaller than that of the static case, and correlated well, unlike the hitter, with the dynamic compressive strength.