Failure behavior and damage constitutive model of granite under different confining pressure unloading conditions

Abstract

This study conducted triaxial unloading tests on granite specimens under different confining pressures, with real-time acoustic emission (AE) monitoring during the experiment. By analyzing the mechanical responses and AE characteristics, this research aims to elucidate the failure mechanisms and crack propagation in granite under unloading conditions, thereby establishing a link between AE characteristics and mechanical responses to further highlight the research purpose and engineering significance. The results, derived from AE ring-down counts, energy release, and event localization, indicate that lower unloading rates lead to a more gradual and distributed failure process, characterized by the formation of numerous and widely dispersed internal cracks. In contrast, higher unloading rates cause more abrupt failure, with fewer internal fractures and crack propagation primarily along pre-existing failure planes. The rise time-to-amplitude ratio (RA) - average frequency (AF) analysis further reveals that the unloading rate significantly influences the fracture mechanism: while shear failure predominates under all tested conditions, the proportion of tensile failure increases with higher unloading rates. Additionally, based on the experimental data, a refined damage constitutive model for granite is proposed. This study contributes to a better understanding of the failure mechanisms of granite during unloading processes and provides a theoretical reference for underground engineering applications involving granite as the surrounding rock, as well as guidance for stability evaluation and excavation design in deep underground engineering.

Keywords

Granite / Confining pressure unloading rate / Acoustic emission / Damage constitutive model

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