A numerical study of brittle failure in rocks with distinct microcrack characteristics

Abstract

A numerical model is presented to reproduce the stress induced fracturing process of brittle rocks. Material heterogeneity at the zone level of the model is considered, and distinct initial microcrack lengths and orientations are also included. The rock material is prescribed with a Weibull distribution, and the microcrack lengths and orientations are defined by distinct distribution functions. Stress intensity factor approach is adopted to characterize the stress condition of the microcracks, and is used as a failure criterion for the zones of the model. The mechanical response of rock specimens is investigated on models under different external loading conditions. Obvious nonlinear characteristics before the peak strength can be observed in models under uniaxial compression. Consistency can be found between simulation results and lab test data. The influence of microcrack conditions and heterogeneity levels on the simulation result is also investigated. The macroscopic failure modes of models are studied with different distributions of initial microcracks, and correlations are found between the microcrack conditions and fracturing processes. Especially, scattered zones and obscure fracture patterns are produced in the model defined by exponential and uniform distribution, compared with clear shapes of macroscopic fractures observed in models defined by normal or lognormal distributions. The simulations also show that the differences in the mean value of microcrack orientations obeying certain distribution result in distinct macroscopic fracture patterns, from shear bands at lower mean orientations to tensile fractures at higher mean orientations. Typical fracture patterns observed in laboratory are successfully reproduced in the model, which demonstrates the capability of the model in reproducing faithful rock behaviors through prescribing specific microscopic characteristics.