Effect of strain-softening and strength anisotropy on the undrained bearing capacity of non-associated clay

The bearing capacity of soils is critical in the design and analysis of foundations. The classical solutions derived from methods of characteristics and bound theories are based on the rigid plasticity and associated flow rule, which may not be realistic for natural soils. The undrained shear strength of soft clays exhibits strain-softening and anisotropic behaviour in laboratory tests, which creates complexity when choosing appropriate strength parameters in the conventional design process. In addition, the stress–strain characters are non-associative and path dependent, which also affects the bearing capacity of soils. This paper investigates two classical stability problems (i.e. deeply embedded pile/pipe section and rigid strip footing) using finite-element analysis and the MIT-E3 soil model, and demonstrates the effects of stain-softening and strength anisotropy on the undrained bearing capacity of soils. The computed results are compared with analytical solutions and finite-element limit analyses, as well as those from finite-element analysis using conventional soil models. These findings have strong practical implications in predicting the bearing capacity of foundations and interpreting in situ tests.