Effect of strain-softening and strength anisotropy on the undrained resistance of deeply embedded pile/pipe section

The bearing capacity of soils is critical for 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 behavior in the lab tests, which creates complexity to choose appropriate strength parameters in 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 one classical stability problem (i.e. deeply-embedded pile/pipe section) using the finite element analysis and MIT-E3 soil model, and demonstrates the effects of strain-softening and strength anisotropy on the undrained resistance of soils. The computed results are compared with analytical solutions and finite element limit analysis. These findings have strong practical implications to predict the bearing capacity of foundations and interpret insitu tests.