Principal strain rotation of anisotropic tuff due to continuous water-content variation

Abstract

Although it is essential for tunnel construction to evaluate the deformation behavior of sedimentary rock due to drying, the reasons for differences in the mechanical properties between dry and wet rock have not yet been clarified. A previous study on Neogene-period anisotropic tuff states that the magnitude correlation of the stiffness in the bedding orientation and its perpendicular one are reversed in the dry and wet states. Although this indicates the rotation of the principal orientation of the anisotropy, the mechanism is unclear. This phenomenon can clarify the stiffness differences between the dry and wet conditions if the deformation characteristics due to drying can be continuously obtained, in detail. In this study, drying tests on Japanese tuff are conducted, and the deformation behavior due to continuous moisture-content variation involving isotropic matric suction are investigated, in detail. The results of two specimens sampled in the bedding orientation and its perpendicular one show anisotropic deformations due to moisture variation. Normal strain in the orientation perpendicular to the bedding plane is dominant and shear strain occurs. Furthermore, principal strain rotation due to moisture variation is detected for the first time. The maximum and minimum principal strain orientations are rotated by approximately 90° from the wet state to dry state. It is determined that the hardest and softest orientations of tuff continuously alternate due to moisture variation.