Introduction: It is well recognized that soil behavior is dependent on the initial stress state and stress path during shear. The complex loading conditions in-situ are not reproduced in typical laboratory tests, which normally simulate plane strain or axisymmetric loading conditions. For example, the deformation characteristics of the soils in a slope depends on the magnitude and direction of the principal stresses, and stress fields beneath foundations include a range of principal stress magnitudes and directions.

Cyclic loading, such as earthquake or wave loading, not only implies a change in the principal stress magnitudes but often also includes a change in the direction of principal stresses. It has been demonstrated that principal stress rotation (PSR) alone at constant deviatoric stress may lead to large plastic deformation and soil liquefaction. But, the influence of principal stress rotation on soil response has rarely been considered in the literature, even though most problems associate with soil liquefaction involves loading that causes principal stress rotation or deformation along with different principal stress directions. Therefore, it is essential to characterize the undrained behavior of soil under such loading conditions for a safe design of geotechnical structures.

Methods and Results: An experimental study of the undrained behavior of sand consolidated to representative initial stress states, and sheared along different loading paths is presented. The behavior of sands along specific principal stress, or principal strain directions with respect to the deposition axis is evaluated under generalized loading conditions using hollow cylinder torsional shear tests. A series of undrained monotonic tests were carried out in water pluviated Fraser river sand using stress or displacement controlled loading. The initial state of the specimen was characterized by stress ratio and static shear. Sand at a wide range of initial stress states was sheared under constant intermediate principal stress or strain, constant principal stress or strain direction, and at constant volume.

Conclusion: The experimental observations indicated that the tendency of strain hardening decreases as the major principal strain aligns towards the bedding (horizontal) plane. The potential flow deformation is strongly dependent on the initial stress state and principal strain direction.

Keywords: hollow cylinder torsion test, principal stress direction, static shear