Energy evolution law and multi-scale failure strength criterion of granite under multiaxial compression

High-strength hard rock and its complex stress environment are one of the challenges faced by deep underground engineering. Mastering the strength characteristics, such as deformation and failure of rock under a multiaxial compression environment, is the basis for solving such problems. This paper proposed a strength criterion based on energy evolution and multi-scale failure characteristics to describe the failure behavior of granite under multiaxial compression. Firstly, the multiaxial compression test of granite was carried out to analyze its stress-strain curve, macro-meso failure characteristics, and energy evolution law, and its meso-failure characteristics were quantitatively characterized based on fractal theory. Secondly, the relationship between shape change energy density, confining pressure, and mesoscopic failure fractal dimension is established, and the rock's multi-scale failure strength criterion is proposed. Finally, the calculation results of the multi-scale failure strength criterion are compared with the test results, Mohr-Coulomb criterion, and Hoek-Brown criterion, and the sensitivity analysis of the parameters in the multi-scale failure strength criterion is carried out. The results show that the multi-scale failure strength criterion can accurately reflect the deformation and failure behavior of rock, and it is proven that the failure characteristics of rock significantly influence the accuracy of its strength criterion. The multi-scale failure strength criterion considers the influence of meso-damage on rock failure behavior, which makes up for the deficiency of the traditional strength criterion in considering damage characteristics and meso-mechanical parameters. It provides a new idea for analyzing rock failure mechanisms and a more accurate prediction model for engineering practice.