Inherent anisotropy of aeolian sand with different bedding angles in true-triaxial tests

True-triaxial experiments were conducted under different stress states with controlled mean principal stress and along various stress paths defined by the intermediate principal stress coefficient to investigate the combined influence of the bedding angle and intermediate principal stress on mechanical behaviour. The experimental results demonstrated that the shear strength and peak internal friction angles varied with the inherent anisotropy regarding the bedding angle. This phenomenon was particularly notable at an intermediate principal stress coefficient of 0.4, under which condition a marked strength reduction occurred due to shear band initiation. Although the influence of the inherent anisotropy was negligible during the initial shear stage, its effects became progressively more pronounced as the shear deformation continued until failure of the specimen occurred, except under axisymmetric conditions. More interestingly, the inherent anisotropy exerted a negligible influence on the critical state of the specimens under axisymmetric conditions, while the combined effect of the intermediate principal stress and bedding angle induced non-uniqueness in the critical state. The experimental results confirm that the manifestation of the effects of the inherent anisotropic on the mechanical behaviour was fundamentally governed by both the existing stress state and the specific stress path applied. The findings of this experimental study provide valuable insights for stability assessments of the common engineering geological issues associated with bedding planes, particularly in complex stress environments.