A Combined Theoretical-Experimental-Numerical Approach to Characterization and Modelling of Rock Fracture and Rock Burst

Abstract

Rock burst is a violent failure of rock in deep underground conditions, which often has severe consequences. Nevertheless, its underlying mechanism is not well understood, let alone being accurately predicted. Existing research studies do indicate the significance of strain energy storage in rock, but questions like, what material properties control strain energy characteristics? How to determine and link it with bursting? How to utilize such a framework further to unveil rock-bursting? Have always been at the center and thus formed our motivational base as well. This research presents a systematic approach to combine theoretical, experimental, and numerical developments towards a size-dependent energy-based rockburst criterion. Along this line, this research develops a new indirect tensile testing methodology named as ‘AUSBIT’ to control the dynamics due to excess strain energy storage in disc cracking under diametric compression. It allows capturing ‘Snap-Back’ behavior and determining inherent fracture, elastic, strength (tensile), and brittleness properties, all from one simple experiment. The devised methodology is patented in Australia as an Innovation Patent. A theoretical framework delineating the snap-back magnitude, which can be considered as a simple bursting indicator, is also developed. Advanced instrumentations such as Digital Image Correlation (DIC) and Acoustic Emission (AE) techniques are utilized to explore the benefits of controlled diametrical cracking and obtain further details on failure mechanism and its evolutions. This thesis also develops a hybrid numerical modeling approach based on Discrete and Finite Element Methods (3DEC, by Itasca). It incorporates a new cohesive contact model with elastoplastic-damage coupling. Laboratory experiments, including uniaxial compressive strength (UCS) and conventional Brazilian disc (BD) test, are conducted with DIC and AE applications to calibrate, validate and demonstrate the competency of the developed numerical modeling approach. At last, this research develops a size-dependent energy-based rockburst criterion linking strength, fracture energies, and specimen size effect with stress state due to changes in boundary conditions. It results in the proposal of a bursting index (₽) to quantify the bursting scale. Experimental data of Bluestone rock obtained from AUSBIT and UCS tests are utilized to illustrate the capability of the proposed theoretical framework. Virtual strain-burst experiments are conducted using the developed numerical modeling approach for verification purposes. This research also provides the links between the conclusions and results from the proposed theoretical framework with the evaluation of in-situ bursting potential in rock masses around underground openings.