A statistical bonded particle model study on the effects of rock heterogeneity and cement strength on dynamic rock fracture

Abstract

Numerical modelling and simulation can be used to gain insight about rock excavation processes such as rock drilling. Since rock materials are heterogeneous by nature due to varying mechanical and geometrical properties of constituent minerals, laboratory observations exhibit a certain degree of unpredictability, e.g. with regard to measured strength and crack propagation. In this work, a recently published heterogeneous bonded particle model is further developed and used to investigate dynamic rock fracture in a Brazilian disc test. The rock heterogeneities are introduced in two steps—a geometrical heterogeneity due to statistically distributed grain sizes and shapes, and a mechanical heterogeneity by distributing mechanical properties using three Weibull distributions. The first distribution is used for assigning average bond properties of the grains, the second one for the intragranular bond properties and the third one for the bond properties of the intergranular cementing. The model is calibrated for Kuru black diorite using previously published experimental data from high-deformation rate tests of Brazilian discs in a split-Hopkinson pressure bar device, where high-speed imaging was used to detect initiations of cracks and their growth. A parametric study is conducted on the Weibull heterogeneity index of the average bond properties and the grain cement strength and evaluated in terms of crack initiation and propagation, indirect tensile stress, strain and strain rate. The results show that this modelling approach is able to reproduce key phenomena of the dynamic rock fracture, such as stochastic crack initiation and propagation, as well as the magnitude and variations of measured quantities. Furthermore, the cement strength is found to be a key parameter for crack propagation path and time, overloading magnitudes and indirect tensile strain rate.