Behaviour of coarse grained soil with rotation path of stress Lode’s angle

In this study, the behaviour of coarse grained soil following the rotation path of stress Lode’s angle is studied under the constant mean stress p and the constant deviatoric stress q in stress space. A large-scale true triaxial apparatus with special friction-reduction technique is used to conduct rotation stress path tests in the deviatoric plane. In each test, the stress Lode’s angle is increased and then decreased between -30° and 30° twice, which covers one-sixth deviatoric plane and represents the whole deviatoric plane due to its symmetry. Under different stress ratios, the volumetric strain, deviatoric strain, strain Lode’s angle and strain path are analyzed together with the rotation stress path. The conclusions are drawn as follows: firstly, soil deforms together with the variation of stress Lode’s angle under the constant mean stress and deviator stress. In the first increasing process of stress Lode’s angle both the elastic and the plastic strains occur. In the following processes, hysteresis can be observed for the deviator strain, volumetric strain, and strain Lode’s angle, the last of which necessarily determines a certain point in strain space. Secondly, the slope of the initial deviatoric strain still increases with the deviatoric stress following the current stress paths. Thirdly, the soil can achieve failure with the increasing stress Lode’s angle, which is affected by the initial stress ratio. Finally, an equation reflecting the variation of strain Lode’s angle is proposed, which should be included in the constitutive model for soil.