A constitutive model for rock interfaces and joints

A constitutive model based on limit concept is proposed to predict the behavior of rock interfaces and joints. For the limit case of an interface with thickness approaching zero, an ellipse yield function is adopted and associated flow rule is recommended. This yield function is not of proportional type, and its motion in stress space is governed by its center position and the hardening rule of yield function. The shear anisotropy is described by a shape function that incorporates the elastic shear stiffness, yield function and hardening rule. An equivalent relative displacement is obtained based on normalized plastic work and limit concept. This equivalent relative displacement yields a hardening rule from which the dilatancy is directly associated with the asperity of the interface. The validity of the proposed constitutive model is verified using data obtained from several existing experimental studies on natural and artificial rock joints.