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    Effect of anisotropy on fracture toughness and fracturing of rocks
    (American Rock Mechanics Association (ARMA), 2015) Ghamgosar, Morteza; Williams, David J.; Erarslan, Nazife
    Elastic parameters of rocks are typically used for design purposes in open pit and underground mining, underground spaces and rock-cutting projects. However, the ultimate strength of rocks is strongly influenced by their micro-fractures, preexisting cracks, and anisotropy due to inhomogeneity, discontinuities, and differing particle sizes or shapes and orientations. Since the fracture behaviour of rocks is important to geotechnical engineers concerned with the design of excavations and underground spaces, it is obvious that laboratory investigations of their anisotropic parameters are necessary for safe designs. The main objective of this paper is to investigate the effect of different orientations of the anisotropy of Brisbane sandstone specimens subjected to diametral compressive (indirect tensile) loading that influences their fracture toughness. To obtain the fracture toughness values of anisotropic Brisbane sandstone, Cracked Chevron Notch Brazilian Disc (CCNBD) specimens were prepared and tested according to International Society for Rock Mechanics (ISRM) standards. The fracture toughness of Brisbane sandstone was found to increase with increasing angle of anisotropy. Based on the experimental results, a statistical regression analysis was conducted to obtain the optimum orientation angle to obtain the highest strength under indirect tensile loading. Statistical analysis showed anisotropy orientations of 45° gave the highest fracture toughness value. Copyright 2015 ARMA, American Rock Mechanics Associa.
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    Investigation the effect of cyclic loading on fracture propagation in rocks by using Computed Tomography (CT) techniques
    (American Rock Mechanics Association (ARMA), 2015) Ghamgosar, Morteza; Stewart, Penny; Erarslan, Nazife
    In Brazilian test, applied diametrical compression stress induces indirect tensile stresses normal to the vertical plane crossing through the rock disc and the ultimate failure occurs at the place where the maximum tensile stress is concentrated. The mechanical behaviour of rock with pre-existing cracks under static loading has been studied widely. In this study, the fracturing behaviour of Brisbane Tuff, under static and cyclic loading has been analysed applying an ISRM standard Cracked Chevron Notched Brazilian Disc (CCNBD) geometry. Specifically, X-ray Computed Tomography (CT) techniques have been used to investigate the fracturing behaviour of rocks under static and cyclic loading. The fracturing behaviour of rocks technically depends on the nature of loading, strength of mineral and text of rocks. Laboratory observations demonstrated that there is a distinct difference in fracturing between the static and cyclic loading. It was found that the cyclic loading had an important effect on micro-fracture propagation through the Fracture Propagation Zone (FPZ). Copyright 2015 ARMA, American Rock Mechanics Association.
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    Progressive damages in hard rock by utilising an oscillating undercut technology
    (CRC Press/Balkema, 2018) Ghamgosar, Morteza; Duffield, Stephen; Erarslan, Nazife
    Rock cutting is a complex phenomenon that requires advanced and sophisticated techniques to predict fracture initiation and propagation under applied or induced mechanical forces. While conventional cutters apply compressive or impact forces to break a rock body, the idea of applying cyclic forces to rock has led to a novel system to break rocks under tension and fatigue mechanisms. Experimental and numerical models have shown that the oscillating disc cutter (ODC), as a new technology in rock cutting industries, can potentially enable more than 30% increase damage in hard rocks, which offers a profitable, safer and cheaper method to underground rock cutting operations. The various physical properties of the rock influence fracturing behaviour in the cutting process, including water content, dry density, porosity and temperature. In addition to the environmental and physical effects, the roles of microfractures and micro-damaging are deterministic, such as structural anisotropy, grain sizes, different mineral compositions, crack size, amplitude and frequency. A noticeable difference in the fracturing behaviour of monzonite specimens was observed under static and cyclic loading. Symmetrical fracture surfaces were seen under static failure, while excessive dust and crushed particles with no evidence of symmetrical fractures were determined under cyclic test. As the main mechanism in ODC is cyclic action at the cutter disc, therefore; this paper discusses laboratory and numerical results of microfractures propagation in Fracture Process Zone (FPZ) under the cyclic loading in order to utilise and optimise for the ODC technology. © 2018 Taylor & Francis Group, London.