A novel hybrid finite-discrete element modeling approach to assess the impact of drilling-induced core damage on laboratory properties of hard brittle rocks

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The Unconfined Compressive Strength (UCS) and Young's modulus (E) of intact rocks are two fundamental parameters required for the design of deep underground excavations. These parameters are usually determined from laboratory unconfined compression tests on cored samples. It is known that the process of core drilling from deep and high-stress environments may induce damage (micro-cracks) to the cored samples due to complex stress paths and high tensile stresses experienced by the core during drilling. Core damage may affect the laboratory properties of rock specimens (e.g., UCS and E). Therefore, research is needed to better understand and predict the impact of core damage on laboratory properties of brittle rocks for a more reliable design of deep underground excavations. The proposed research aims to develop a novel methodology in a commercial numerical modelling program based on the hybrid Finite-Discrete Element Method (FDEM), known as Irazu, to investigate the influence of coring stress path on brittle damage and associated changes to the properties of hard, brittle rocks. The objectives of this research are: a) to determine the most suitable boundary conditions to apply 3D coring stress paths to simulate core damage in 2D FDEM models; b) to develop a systematic methodology to calibrate the FDEM model to the laboratory properties and behaviour of undamaged and damaged rock specimens with one set of input parameters; and c) to investigate the influence of heterogeneities (pre-existing microcracks and mineral grains of various Young's moduli) on density and characteristics of unloading-induced microcracks. This research will be completed by making recommendations on the impact of borehole orientation and drilling depth on the level of core damage. This work is anticipated to develop new methodologies and tools in the Irazu software to predict drilling-induced core damage and reliable estimate the in situ rock strength and deformation properties.