Colinearity of Stresses, Strains, and Strain Increments during Shearing of Soft Clay

Abstract

The results of torsional shear tests on a normally consolidated marine clay have been analyzed to check the common assumption of colinearity between the principal directions of stress and plastic strain increment. Shear strain increments measured during the tests were divided into elastic and plastic components using three different plastic models: an isotropic hardening model, a kinematic hardening model, and a model in which all shear strain was assumed to be plastic. These three cases are believed to bound the possible divisions, which may be obtained using more sophisticated models. Colinearity was not observed for any of the models over most of the shearing range. All the models indicated that at the onset of yielding, the principal plastic strain increment directions are close to those of stress increment, and they approach those of stress toward failure. A new parameter, psi-ratio, was introduced, defining the principal direction of the plastic strain increment relative to those of the stress and t...