Mechanical properties of saturated and unsaturated cohesive soils with stress-induced anisotropy

When anisotropic stress is applied to a soil, stress-induced anisotropy of mechanical properties develops. Using a hollow, cylindrical torsional shear apparatus, this study examined the effects of stress-induced anisotropy on the mechanical properties of saturated and unsaturated cohesive soils under different drainage conditions. Although strength anisotropy did not appear under a drained condition, it developed under undrained conditions in both saturated and unsaturated cohesive soils. The secant shear modulus exhibited a trend of becoming smaller as the angle between K consolidation and shearing became larger under both drained and undrained conditions. With regard to strength, the experimentally obtained results elucidated that the changes of excess pore water pressure and suction during shearing generated strength anisotropy. Using suction at the failure point reveals that the shear strength follows the failure criterion proposed by Fredlund and co-workers in 1978, even in a specimen with anisotropy of strength.