Characterization of Brittle Damage in Rock from the Micro to Macro Scale

An Increasing need for mining and constructing underground facilities at a greater depth and under high in-situ stresses have introduced new challenges in the form of brittle rock fracture. Brittle fracture is a complex mechanism comprising different stages of failure including initiation, propagation and coalescence. Brittle fracture studies in rock can be undertaken at a wide range of scales from the micro scale i.e. microcrack/grain scale in laboratory samples through the meso scale (underground excavations) to the macro scale such as in-situ engineered/natural rock slopes or block cave mines. At all these scales the rock/rock mass is subjected to “damage” which influences the engineering performance. Improved understanding of brittle damage at various scales requires development of damage intensity measures to quantify brittle fracture for both pre-existing and stress-induced fractures and the use of advanced numerical modelling approach. In this study, a state-of-the-art numerical modelling approach based on the combined finite/discrete element method (FDEM) is integrated with discrete fracture network engineering, DFNE, in order to evaluate brittle damage at varied scales. The influence of micro-heterogeneity is studied at the laboratory scale by incorporating a micro discrete fracture network (µDFN). A wide range of laboratory testing including Brazilian, uniaxial, biaxial and triaxial compression tests are modeled to investigated the complete 3D fracture process. At the meso scale, mechanisms leading to strain bursting and spalling damage around underground openings are studied focusing on the influence of pre-existing cracks in a massive rock mass. Finally at the macro scale, a finite/discrete element modelling approach coupled with a discrete fracture network (FDEM-DFN) is utilized to analyze the hanging wall surface subsidence associated with sub-level caving. A suite of model data interpretation methods including time-displacement hanging wall deformation characterization, numerical inverse velocity analysis and virtual hanging wall inclinometers is adopted to improve our understanding of the extent and mechanism of hanging wall failure with mine advance.