Abstract: An elastoplastic fracture model for jointed rock mass under compressive loading is presented. In order to account for the mixed mode plastic zone model of wing crack tip of jointed rock under small scale yielding, the dimensionless function of the plastic zone diameter based on the Drucker-Prager (D-P) criterion is derived. The plastic zone models of mode I, mode II and mixed-mode (I+II) are compared with plastic zones obtained by Mises criterion and the influences of different Poisson's ratios for mixed-mode plastic zones of wing crack tip are studied. It is shown that the mode I and mixed-mode plastic zones of D-P criterion are larger than that of Mises criterion; and its mode II and mixed-mode plastic zones are not continuous between the upper and lower surfaces of wing crack. Moreover, plastic yield criterion is employed simultaneously with the fracture softening to describe the behaviors of jointed rock based on D-P criterion. The conception of fracture softening factor is introduced to characterize the softening feature of crack propagation. Regarding the strain energy density of wing cracks at joint-tip is responsible for the evolution of fracture softening of jointed rock. Thus, the behavior of fracture softening can be developed by proposed function of strain energy density. Borja’s strain hardening/softening function is employed as the plastic yield function, regarding the plastic inner variables and stress as two impact factors of the hardening function. The elastoplastic fracture model with its numerical algorithm is proposed; and the code of elastoplastic fracture model is implemented by using return mapping implicit integration algorithm. The influences of friction coefficients, initial joints orientation and stress intensity factor on the constitutive response under uniaxial compression are studied. The results are generally in good agreement with experimental data of uniaxial compression tests of jointed marble.

Key words: jointed rock mass, strain energy density, plastic softening, fracture softening factor, implicit integration algorithm, D-P criterion, crack tip plastic zone