Influence of End Restraints on Strain Responses of Anisotropic Tuff During Triaxial Compression

In triaxial tests, the rock specimen is often assumed to have an axisymmetric elementary response. However, the axisymmetric condition of deformation is not always satisfied for anisotropic rocks, because the incremental relationships between stresses and strains are not necessarily coaxial. Furthermore, rock specimens often exhibit non-uniform deformation owing to the effect of end restraints. The influence of end restraints on the deformation behavior is significant in anisotropic rocks when compared with that in isotropic rocks. In this study, four types of consolidated drained triaxial tests were conducted on anisotropic tuff under different conditions involving end restraints. All components of the strain tensor were measured using multiple strain gauges attached to the side of the specimen. Although the normal strains were not considerably influenced by the presence or absence of the cap and Teflon sheets at the top end of the specimens, the shear strains and orientations of the principal strains were significantly influenced by the end restraints. These results indicate that anisotropic elastic parameters determined using shear strains vary widely owing to end restraints.