Abstract:The constitutive models for rock interfaces and joints under cyclic normal loading are reviewed. From many tests it is concluded that the joint loading,unloading and reloading follow hyperbolic responses,and result in irrecoverable closure deformation with hardening of the joints. Based on the hyperbolic constitutive models,it is supposed that the unloading and reloading curves have the same asymptote which represents the maximal closure of the joint. For every loading step curve,the initial normal stiffness,which is defined as the normal stiffness at the zero normal stress point on the curve,is calculated from the initial normal stiffness of the previous loading and unloading curves. New parameters are introduced to represent the convergence velocity of constitutive curves and the irrecoverable closures,with their values depending on the rock types,the geometric characters and on the infill mineralogy of the rock interfaces and joints. With different values of the parameters,this model can be made equivalent to other models reviewed. Comparison with normal cyclic loading tests on natural clean joints and filled joints shows that this model could describe the constitutive relations of rock interfaces and joints with higher accuracy.