Non-axisymmetric and/or non-elementary response of anisotropic tuff in axisymmetric, elementary triaxial test

Specimens of triaxial tests ordinarily response as element in the axisymmetric condition, and it is theoretically correct assumption. However, for anisotropic rocks, the axisymmetric condition is not always satisfied because incremental relationships between stresses and strains are not coaxial. In addition, such rock specimen often shows non-uniform deformation behaviors due to end frictions. As the reason, the influence of end restraints on deformation behaviors of anisotropic rocks during triaxial compression is much greater than that of isotropic one. In this study, the variations in the stress-strain relationships of anisotropic tuff due to the condition of end restraints are investigated. The results of four consolidated drained triaxial tests with measuring the strain tensor demonstrated that the axial and volumetric strains were not influenced by whether sliding mechanism and Teflon sheets are installed at the end of specimens or not; meanwhile, the shear components of the strain tensor and the inclinations of principal strain orientations are widely varied owing to the end restraints.