Abstract:
Rockwall excavated at great depth often experiences largeductile deformation and may be failure due to high compressive in-situstresses. Such phenomena are closely related to anisotropic distribution ofjoints in rock masses and mechanical response of the rock block and thejoint. To take into account the shear resistance of joint surface andanisotropic inelastic deformation related to secondary joints formation, acoupled elasto-plastic microplane damage model for jointed rock masses isdeveloped in the framework of microplane model and damage mechanics. Eachmicroplane of a jointed rock mass is regarded as a binary medium, which iscomposed of rock and joint. Joint connectivity on the microplane isintroduced as the damage variable to characterize area damage of the rockmass on that orientation due to presence of the joints. By adoptingdifferent yield function and damage evolution law for the microplane undertensile and compressive normal stress respectively, the coupled mechanismsof inelastic deformation and damage evolution are modeled. Rate formconstitutive relation of stresses and strains on microplanes is developedbased on classical plastic theory. According to the kinematic constraintcondition of microplane model, macroscopic constitutive relation is obtainedthrough directional integration along all microplanes. The presentelasto-plastic microplane damage model is implemented to the commercial FEMsoftware MARC through a user subroutine. Simulations with respect to theuniaxial tension and compression of jointed rock masses and problem ofwellbore stability under inner mud pressure are presented respectively. Ithas demonstrated that the coupled effect between anisotropic inelasticdeformation and damage evolution of jointed rock masses can be characterizedefficiently with the model.
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