To model rocks＇ deformations and failures at high compressive stresses, a composite yield function was proposed in an elastic and brittle constitutive model with damage, which includes a linear shear yield function with tension-off（ i. e. , the Mohr-Coulomb criterion）and a nonlinear shear yield function （i. e. , the Hoek-Brown criterion）. A damage factor was introduced into the model to take the decrease of elastic modulus into account in the stress drop process of brittle rocks. The factor describes the damage extent. The influence of confining pressure on the elastic modulus was considered. The failure process of a rectangular specimen in plane strain compression was modeled. The obtained results were compared with those of the quite brittle strain-softening Mohr-Coulomb model with tension-off. Apparent difference was found. A plane strain model after a circular tunnel was excavated in hydrostatic pressure was modeled and the distribution of failed elements, slight rockburst regions due to shear and tensile failures and bulk modulus was presented. It is found that when the influence of confining pressure on the elastic modulus is considered, there exists higher bulk modulus at tips of V-shaped notches. In notches, the damage extent of rock elements is increased with an increase of the damage factor. If the elastic modulus is independent of the confining pressure, then blunt V-shaped notches with larger sizes are expected. The present results show that the one reason for the difference in pattern of V-shaped notches of different rocks is the different damage extent in the brittle failure process and the different influence extent of confining pressure on the elastic modulus.
Journal of Basic Science and Engineering
non- linear yield criterion