Research on evolution law of coupled macro-micro damage release rate of fractured limestone under uniaxial compression test
摘要
Limestone region is characterized by a complex and extensive karst network, featuring a variety of fracture shapes that can be categorized into four primary types: cracks, elliptical holes, mushroom-like holes, and dumbbell-like holes. Compared with intact limestone, the presence of fissures significantly influences the mechanical properties, energy characteristics and the mechanism of microcracks in limestone. Furthermore, energy release rate, which is the core of the Griffith fracture criterion, effectively characterizes the crack propagation process of rock mass. To investigate energy characteristics and the mechanism of micro-crack initiation and propagation evolution during the deformation and failure of fractured limestone, a formula for the coupled micro-macro damage energy release rate is derived, based on nonlinear dynamic theory, Lemaitre strain equivalent hypothesis, and energy theory. This was followed by the determination of the micro-crack propagation law under Unconfined Compressive Strength (UCS) testing conditions. The results indicate that, according to the energy dissipation theory, the order of energy accumulation is as follows: mushroom-like hole, fissure, elliptic hole, intact limestone, and dumbbell-like hole. Based on energy dissipation characteristics, coupled macro-micro damage energy release rate and stress-strain curve, the deformation and failure stages of fractured limestone and intact limestone can be divided into five stages: stress adjustment stage (Stage Ⅰ), stable closing of micro-cracks or micro-pores (Stage Ⅱ), low-speed propagation of micro-cracks (Stage Ⅲ), rapid propagation of micro-cracks (Stage Ⅳ), and the formation of main macroscopic fractures (Stage Ⅴ). The mutation point of energy release rate in Stage Ⅳ prior to the peak can serve as an identification point of failure precursor of rock samples. The research results can provide theoretical guidance for analyzing geological hazards in karst areas.