Abstract: A strain-softening model with broad applicability is proposed with respect to the Hoek-Brown (H-B) criterion based on forty triaxial test results of different hard and soft rocks. Firstly, based on the test results, the three-parameter power-type confining pressure function is verified to be correct for describing the relationship between the post-peak critical plastic stain and confining pressure for different types of rocks, and is introduced into the definition expression of the plastic internal variable. Then, the rationality of the different parameters for describing the softening parameters of the strain-softening model based on H-B criterion is compared and analyzed. It is found that the parameter GSI is best suited for the description. Moreover, the evolution of GSI with the plastic internal variable in the post-peak stage is studied, and a widely applicable nonlinear model is established. By comparing it with the other existing models, it shows that the proposed model can describe the nonlinear evolution of strength parameters of H-B criterion in the post-peak stage more correctly with fewer parameters. The model is applied in the software ABAQUS by adopting the non-associate flow rule. Finally, by simulating the different laboratory tests of rocks, it is proved that, with good applicability, the proposed model can correctly characterize the strain-softening and dilation behavior in post-peak stage of hard and soft rocks under different confining pressures. By comparing it with the models of constant critical plastic strain or constant dilation angle, respectively, it is found that the simulated stress-strain curves by the proposed model are more closely in line with the test results.

Key words: rock mechanics, Hoek-Brown criterion, plastic internal variable, strain-softening, dilation