Experimental and Numerical Investigations into Fracturing Process of Brittle Rocks

Tensile strength plays a vital role in the efficient design of underground openings and support system in rock engineering practice. Among various approaches developed for estimating this property, Brazilian testing has received considerable attention in analytical, numerical, and experimental studies. The test has been deployed for various materials such as rock and concrete; however, its fracturing process at micro and macro scales has not yet been thoroughly characterized. In this study, a coupled experimental-numerical technique was used to characterize the failure process of granite to better understand the fracturing process of brittle rocks under indirect tensile loading. In the experimental part, two independent monitoring techniques, Acoustic Emission (AE) and high-speed imaging, were deployed to investigate micro and macro cracking processes. The sample's behaviour was then simulated using a Distinct Element Method (DEM) code through Trigon logic to further compare the brittle failure characteristics with the experimental results. The collective results revealed that the tensile microcracks are the first to initiate during the failure with higher intensity compared to shear microcracks, resulting in a dominant tensile failure at macro scale. Also, it was noted that the sample's failure started from the center, which keeps the Brazilian results valid for brittle rocks while some overestimations may be added due to following shearing and the lack of enough stiffness in the testing machine. 1. INTRODUCTION The initiation of fractures in brittle rocks can occur through tensile events, highlighting the significant role of tensile strength in the design of rock engineering projects (Griffith, 1921, Tapponnier and Brace, 1976, Stacey, 1981, Diederichs and Kaiser, 1999, Perras and Diederichs, 2014, Khadivi et al., 2023). Therefore, accurate assessment of tensile strength and cracking mechanism is essential for better understanding the mechanical behavior of brittle rocks. The convenience of sample preparation and straightforward testing operation have made the Brazilian test the most popular approach to estimate the tensile strength across a wide range of materials (Hobbs, 1964, Barla and Innaurato, 1973, Jonsén et al., 2007, Bahaaddini et al., 2019). Valid testing results are obtained by inducing a tensile fracture at the center, splitting the sample along the compressive diameter into two halves (Colback, 1966, Carmona and Aguado, 2012).