An experimental investigation and mechanical modeling of the combined action of confining stress and plastic strain in a rock mass

A series of nonlinear characteristics, such as strain softening, elastic-plastic coupling, and plastic deformation failure, have focused attention on postpeak deep rock masses. However, one-dimensional models, such as the Mohr-Coulomb (M-C) and strain-softening (SS) models, do not consider the influence of confining pressure, which can increase inaccuracies when used for simulating rock deformation in deep underground engineering. In this study, the composite effect of plastic damage accumulation on the mechanical properties of surrounding rock under different confining pressures was investigated through triaxial cyclic loading-unloading tests. A two-dimensional mechanical model for the cohesion, friction angle, elastic modulus, and dilatancy angle was developed by considering the combined effect of the confining pressure and plastic shear strain. The results showed that the cohesion and friction angle could be determined using an exponential function and a line function, respectively, with plastic deformation and confining pressure. The correlation coefficient of the two-dimensional function reached 95%. The elastic modulus increased with the confining pressure as a negative exponential function but decreased with the plastic deformation as a linear function. The dilation angle linearly decreased with the confining pressure and first increased and then decreased with the plastic deformation, which could be determined by the difference between two exponential functions. Through the use of FLAC3D software, the strain-softening model developed in this study was used to simulate a triaxial rock compression test, and the result demonstrated that the modified model was accurate and reasonable.

Automated summary

This study investigates the composite effect of plastic damage accumulation on the mechanical properties of surrounding rock under different confining pressures through triaxial cyclic loading-unloading tests. A two-dimensional mechanical model is developed to describe the cohesion, friction angle, elastic modulus, and dilatancy angle by considering the combined effect of confining pressure and plastic shear strain. The modified model is proven to be accurate and reasonable through simulation using FLAC3D software.