Abstract: For the analysis of the rock engineering concerned with rock discontinuities which should be taken into consideration separately; it is of great importance to adopt the valid constitutive model for rock discontinuities which can account for the major observed mechanical properties of rock discontinuities. Due to the limitation of available constitutive models for rock discontinuities within the framework of classical continuum mechanics, a new constitutive model for rock discontinuities is presented by taking use of the direct methodology based on the strength and deformation behaviors of rock discontinuities. In the presented model, the tangential stress and deformation curve and dilatancy curve are divided into linear part before peak point, nonlinear part before peak point, and softening part after peak point; and the mathematical models which can accurately characterize the major mechanical behaviors of rock discontinuities are given. Then, based on the above-mentioned, the incremental constitutive model for rock discontinuities is developed. Finally, two classical direct shear tests of rock discontinuities are simulated by the developed model and the Plesha’s model which is used widely The results show that the major mechanical behaviors of rock discontinuities can be reasonably described by the presented model. The simulation ability of the presented model is better than the Plesha’s model.

Key words: rock discontinuities, constitutive model, dilatancy, plastic softening, rock mechanics