Abstract: Based on triaxial compressive experiments of hard rock simulated by numerical method, the influence of intermediate principal stress on the fracturing mechanism of homogeneous and heterogeneous rocks is analyzed with four constitutive models, i.e. Mohr-Coulomb, Drucker-Prager and strain-softening considering deformation modulus degradation or not. The results show that the intermediate principal stress has a larger effect on the strength of rock using Drucker-Prager model than that using other models, whether the rock is homogeneous or heterogeneous. And it has a large impact on the failure process and mode of heterogeneous rock using strain-softening model. For the example in this paper, the strength of homogeneous or heterogeneous rock varies considerably with different constitutive models. Although the rock uses the same constitutive model, the strength of homogeneous rock is much larger than that of heterogeneous rock except for Drucker-Prager model. Because the responses of engineering rock masses to the intermediate principal stress are different, proper constitutive model should be chosen based on the characteristics of rock masses in order to guarantee engineering safety during the design process of underground structure.

Key words: rock mechanics, intermediate principal stress, hard rock, fracture mechanism, rock strength, constitutive model, heterogeneity