Effect of strength anisotropy on undrained slope stability in clay

The influence of strength anisotropy on the two-dimensional undrained slope stability analysis in soft clay is evaluated herein. Because of the inherent anisotropy of clay, the mobilized undrained shear strength tends to vary as the inclination of the failure surface changes. To deal with this problem, the limit state analysis and a total stress strength criterion, which represents the anisotropic undrained shear strength along the slip surface, are used to calculate the anisotropic factor of safety against sliding (F_s,A). However, since it is too complicated in practice for engineers to directly apply the anisotropic shear strength to the slope stability analysis, a method is proposed here to calculate the anisotropic factor of safety in terms of the location of the slip surface and the soil strength anisotropy ratio (A_r = S_ue/S_uc) obtained from the CK₀U triaxial extension and compression tests, respectively. For any given slip surface, its F_s,A can be calculated from the F_s,A/F_s,I ratio determined with the proposed method, where the isotropic factor of safety (F_s,I) can be determined from the routine isotropic slope stability analysis. However, it should be borne in mind that the slip surface with the lowest F_s,I may not necessarily be the same slip surface with the lowest F_s,A. Therefore, the methods used to determine the slip surface of the lowest F_s,I should be adopted to locate the slip surface with the lowest F_s,A. Finally, the influences of slip surface location and strength anisotropy ratio on the F_s,A are also evaluated.