Elastoplastic damage behavior of quasi-brittle rocks considering crack closure evolution

Crack closure evolution in compaction stage of quasi-brittle rocks is a very common phenomenon. A distinct feature of quasi-brittle rocks is that, under compression, presence of microcracks can increase nonlinear mechanical response of rock under low confining pressure, while gradually decrease nonlinear behavior of rock under high confining pressure. Previous studies have mainly focused on modelling the damage evolution caused by plastic strain, with few attempts to describe nonlinear behavior of compaction stage and reveal elastic damage dissipation mechanism triggered by the crack closure evolution. This paper presents a coupled elastoplastic damage model, which incorporates crack closure to describe the distinct behavior of rock based on the frame-work of continuum thermodynamics. Comparison between the model predictions and test results of three rock specimens shows that the model can capture whole process mechanical behavior of quasi-brittle rocks over a wide range of confining pressure using a set of model parameters. Parametric studies are carried out to quantify the effects of crack closure evolution and dissipation mechanism of elastic damage and plastic flow of the rock. The proposed model based on an implicit return mapping algorithm has been used to simulate the plastic damage response of rock specimen under displacement control.