An improved elastoplastic model for rocks and application to cyclic loading and unloading triaxial compression tests

The recoverable strain of rock is completely classified as elastic strain in the conventional elastic-plastic theory, which often results in poor agreement between theoretical and experimental curves. This work proposes an improved elastoplastic model of rock materials considering the evolutions of crack deformation and elastic modulus to better characterize the nonlinear mechanical behavior of rock in the post-peak stage. In this model, the recoverable strain is assumed to be a combination of elastic and crack strain, and the constitutive relationship between crack strain and rock stress is deduced. Based on the proposed assumption, the evolutions of the mechanical parameters including strength parameters, elastic, plastic, and crack deformation parameters versus the plastic strain and confining stress were investigated. The developed elastoplastic model was validated by comparing the theoretical values with the results of the triaxial cyclic loading and unloading test. The theoretical calculation results show a good agreement with the laboratory test, which indicates that the improved elastoplastic model can effectively reflect the nonlinear mechanical behavior of the rock materials. The research results are expected to provide a valuable reference for further understanding the evolution of rock crack deformation.