Effects of soil structure and anisotropy on undrained shear behavior of natural clays

This paper presents an experimental investigation on the effects of soil structure and anisotropy on the undrained shear behavior of natural clays. A series of laboratory K0-consolidated undrained (CK0U) and isotropically consolidated undrained (CIU) triaxial tests were conducted on both undisturbed and reconstituted clay specimens. Test results showed that the undrained shear strength for both undisturbed and reconstituted specimens obtained from the CK0U test is higher than the CIU test at a given effective global stress (p′). Comparison of the difference in undrained strength showed that the effect of soil structure on undrained shear strength will gradually lose with the increasing consolidation stress while the effect of soil anisotropy will gradually increase with the increase of the consolidation stress. The effect of soil structure and anisotropy on soil cohesion is negligible. The soil structure and anisotropy mainly affect the total friction angle of specimens yet the influence on the effective friction angle is slight. Undrained shear strength of natural undisturbed clay samples consolidated isotropically or anisotropically can be well predicted using the piecewise function proposed in the present study.