Progressive damages in hard rock by utilising an oscillating undercut technology

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.