Effect of loading rate on the brittleness index of granite: An experimental investigation

Abstract

In deep underground engineering, rock brittleness is closely associated with rockburst and feasibility of hydraulic fracturing. The loading rate plays a crucial role in determining the severity of rockburst and cuttability. By conducting uniaxial compression tests and single-cycle loading-unloading experiments, the brittle evolution of four types of granite under different loading rates was investigated. During the uniaxial compression process, acoustic emission parameters were used to characterize the crack evolution patterns. Additionally, the macroscopic failure process of the specimens and the post-failure rock fragments were recorded with a high-speed camera, providing multi-scale validation. This study proposes a quantitative brittleness index based on rock fracture energy, and its validity is verified by analyzing the rock failure process and the macroscopic characteristics of rock fragments.: This work contributes to advancing research on rock brittleness indices considering the coupling between energy evolution and kinematic mechanisms. The research results indicate that as the loading rate increases from 0.1 mm/min to 5 mm/min, the quantitative evaluation index (B_s) for brittleness increases from 0.17 to 0.28, while the qualitative evaluation indices M_F (projectile mass ratio) and $\overline{l}$ (average lumpiness) increase from 0.3261 to 0.4184 and from 32.96 mm to 38.12 mm, respectively. With increasing loading rates, the brittleness of the rock increases significantly. A series of qualitative and quantitative results, including fractal characteristics and acoustic emission parameters, reveal the crack evolution patterns of granite under different loading rates and confirm the rationality of the brittleness index. This study provides theoretical guidance for practical deep underground engineering applications.

Keywords

linear energy storage law / brittleness index / fracture mechanism / projectile mass ratio / average lumpiness

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