![]() ![]() The cracking mode is dominated by tension failure, with a small proportion in shear (between 3.5% and 1.5%). Cracks can be induced in mineral grains and along the grain interfaces. It is found that hydraulic fracturing of crystalline rock involves many unique behaviours on grain-scale such as non-symmetrical propagation, "zipper mode" initiation time order, generations of isolated and branching cracks, and re-closure of the cracks earlier initiated. Next, sensitivity analysis of in-situ stress conditions is carried out. First, typical micro behaviour and hydro/hydro-mechanical responses are presented and interpreted. Three laboratory-scale fracturing cases over granite under different in-situ stresses are simulated. The micro-heterogeneity of the rock is represented by a grain-based model. To fill the gap, this paper proposes a coupled hydro-grain-based discrete element model and explores the fluid-driven micro-cracking of crystalline rock. However, the heterogeneity has been insufficiently considered in hydraulic fracturing. The grain-scale heterogeneity of rock has been found to greatly affect the cracking behaviour in mechanical tests.
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