Study on mechanical properties and elasto-brittle-plastic constitutive model of hard brittle rock based on conventional triaxial test

Due to the degradation of the elastic modulus and Poisson’s ratio, hard brittle rock is characterized as non-linear mechanical properties. Elastic modulus, Poisson’s ratio, and strength parameters show non-linear characteristics with increase of confining pressure, due to the microcracks in hard brittle. The pre-peak deformation process of rock is divided into four stages based on the variation of microcracks to characterize the asymptotic deformation process of rock. The variation of elastic modulus, Poisson’s ratio, and strength parameters with confining pressure are acquired in different stages. The results show that the elastic modulus E is not only related to the confining pressure, but also related to the deformation and damage state of the rock; in addition, the deformation and damage state of the rock depends on the activity state of the microcracks. The elastic modulus at each stage increased significantly with the increase of the confining pressure. The Poisson’s ratio v\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v$$\end{document} of the rock samples under different confining pressures at the same deformation stage is relatively close and approximately constant. On this basis, an elasto-brittle-plastic constitutive model reflecting the non-linear mechanical characteristics of hard brittle rock before the peak is established. The model is composed of non-linear elastic stage, strain softening stage, and plastic flow ones, which is applied to numerically simulate hard brittle rocks under different confining pressures, and the obtained stress–strain curves are consistent with the test curves, reflecting the pre-peak nonlinear mechanical behavior of hard brittle rocks. This study will be conducive to deformation, stability analysis, and engineering design of deep roadway and tunnel under high in-situ stress.