Abstract: The conventional triaxial tests, triaxial tension (extension) tests and combined compression-tension triaxial tests on core clay materials of Nuozhadu and Shuangjiangkou earth-rockfill dams are carried out by using the developed horizontal triaxial tension-compression apparatus. Based on the test results, the stress-strain behaviors of compacted clay under triaxial compression, triaxial tension and compression-to-tension states are investigated. Furthermore, the applicability of Duncan-Chang’s EB constitutive model is extended, so that it can be used to describe the deformation properties of compacted clay from compression state to tension one. This extended Duncan-Chang model can be used for numerical simulation of tensile crack propagation in soil structure.