Evolution models of the strength parameters and shear dilation angle of rocks considering the plastic internal variable defined by a confining pressure function.

Based on the triaxial test results of 30 types of rocks, by analysing the confining pressure function and defining a new plastic internal variable, the evolution laws of the strength parameters and shear dilation angle with a defined plastic internal variable are studied, and the corresponding evolution models are established. First, the complete stress-strain curves of 30 types of rocks are collected from published literature; from these curves, the critical equivalent plastic strains under different confining pressures are extracted. With the confining pressure and critical equivalent plastic strain data of the 30 types of rocks, fitting is performed for 23 different functions. The results demonstrate that the three-parameter allometric power-type function is the best to serve as the confining pressure function to define the plastic internal variable. Second, the strength and plastic strain data of the 30 types of rocks are extracted and transformed into the strength and plastic internal variable data. By analysing the evolution laws of the strength parameters considering the plastic internal variable, the Gaussian function is adopted to uniformly characterise the variation in the strength parameters with the plastic internal variable. Third, the shear dilation angle, confining pressure and plastic strain data of the 30 types of rocks are extracted and transformed into shear dilation angle, confining pressure and plastic internal variable data. By analysing the evolution law of the shear dilation angle considering the confining pressure and the plastic internal variable, a negative exponential function is adopted to uniformly characterise the nonlinear evolution of the shear dilation angle. Finally, the proposed evolution models of the strength parameters and the shear dilation angle are integrated into ABAQUS. By comparing the simulated complete stress-strain curves with the experimental curves of the different rock types, it is verified that the proposed models can be used to correctly simulate the nonlinear deformation and failure of different rock types. This research overcomes the shortcomings of the existing models and has wide application prospective. [ABSTRACT FROM AUTHOR]