Abstract: Based on a large number of experimental data, the evolution law of strength parameters and dilation angle in hard rock elasto-plastic deformation and failure process is studied to establish their evolving models. Firstly, by analyzing the relationship between critical plastic strain and confining pressure of twenty-six types of hard rocks, a widely suitable three-parameter power-type confining pressure function is proposed and introduced into the definition of the plastic internal variable. The evolution law of strength parameters and dilation angle with the plastic internal variable in the plastic strain hardening-softening process is studied with respect to the Mohr-Coulomb criterion. The Gaussian model for describing the nonlinear evolution of strength parameters is then proposed, and the evolving model of dilation angle considering the influence of both confining stress and plastic internal variable is established. And then, considering that the pre-peak stress-strain relationship of hard rocks is usually simplified as linear in practical engineering, the strength parameters and dilation angle evolving models specifically in the post-peak process are studied. Finally, by comparing the simulated and experimental results of multiple sets of hard rocks, it is found that the models of strength parameters and dilation angle in the plastic strain hardening-softening process can correctly reproduce the axial and circumferential deformation under different confining pressures. The proposed evolving models can also reasonably describe the post-peak deformation in the plastic strain-softening process under different confining pressures. The proposed models are applicable and showing good prospect for different types of hard rocks.

Key words: rock mechanics, hard rock, strength parameters, dilation angle, evolving model