Constitutive relation and integration algorithm for rock discontinuities under cyclic loading

The discontinuities distributed in underground structures are the important factors that affect the mechanical characteristics of rock mass, and to study the mechanical behavior of rock discontinuities under cyclic loading is of great engineering significance. In light of the non-associated plastic theory, defining the dilatancy and reduction zones, a constitutive model for rock discontinuities considering the coupling of dilatancy and plasticity is established. Starting from the basic damage mechanism, with regard to the separation of tension and shear, a new damage constitutive model based on the energy theory is proposed. In which the tension and shear plastic Helmholtz free energy and damage energy release rates are determined by using the basic principle of plastic mechanics in the effective stress space, and the tension and shear damage failure criteria for rock discontinuities are proposed. Aiming at the strong nonlinear performance of rock discontinuities under cyclic loading, the operator decomposition method is introduced. The coupling process of dilatancy and plasticity, as well as the damage evolution process, is solved separately, and a mixed integration algorithm for the elastoplastic damage constitutive relation of rock discontinuities is put forward. Some experiments of direct shear and cyclic shear are simulated respectively, and the agreements between the simulated results and the experimental data indicate that the proposed model is reasonable and effective to simulate the complex deformation of discontinuous rock mass.