Abstract: True triaxial tests on clay mixed with gravel were carried out under complex stress state to simulate the loading process of core wall elements under water storage process, and loading was applied from the minor principal stress direction. Under initial state, the major principal stress and the second principal stress were adjusted with constant minor principal stress; initial anisotropic stress state was reached to simulate the stress state of dam elements. The major principal stress and second principal stress were then kept constant. Minor principal stress increment was applied to simulate the stress path that core wall elements go through during the process of water storage. Test results show significant differences compared with the result of conventional triaxial tests and true triaxial tests loading from major principal stress direction. Under different initial stress conditions, the initial tangent modulus and initial Poisson’s ratio of the principal stress direction are very complex, and the stress - strain curve shows obvious anisotropy. In the process of core wall rockfill dam construction and the water storage process, the stress path experienced by the core wall unit is obviously different. The reasonable soil constitutive model should be used to describe the modulus and Poisson’s ratios caused by the different loading paths.

Key words: true triaxial test, minor principal stress, anisotropy, clay mixed with gravel, stress path