Effect of strength anisotropy on strain localization in natural clay

Strain localization in soils causes the failure of slopes and foundations. Shear strength is an important factor that affects strain localization in soils. It is well known that the shear strength of natural clay is highly anisotropic due to the internal soil structure. An anisotropic failure criterion for natural clay is presented in which an anisotropic variable is used to describe the relative orientation between the stress directions and soil fabric. The failure criterion is employed in a Drucker–Prager model that considers the strain softening of natural clay. The effect of anisotropic strength on strain localization in clay is analyzed by two examples, including an undrained slope stability analysis and a simulation of a hollow cylinder test of Boom clay. It is found that the shear strength anisotropy affects both the strain localization pattern and factor of safety for the undrained slope. Simulation of the tests on Boom clay shows that the model with the anisotropic yield criterion yields an eye-shaped strain localization pattern that cannot be obtained by the model with the isotropic yield criterion.