The deformation of clay is controlled by the contact between grains which is classified as perfect contact and sliding contact in this paper. In the elastic deformation phase

the contact between grains is regarded as perfect contact. With the increase in shear stress

there are gradual conversions from perfect contacts to sliding contacts which are viewed as damages in this paper. Based on Mohr-Coulomb law

a calculation method for the damage ratio is given according to the relative distance of the stress point to the initial damage line and failure line. On this basis

a damage constitutive model is proposed. The model properties can be simply obtained through the conventional triaxial compression test. Consolidated-undrained test results indicate that the model is capable of predicting the shear deformation behavior of clay under various conditions

including varying hydrostatic stresses and stress paths.