ABSTRACT
Elaso-plastic constitutive models such as the (original) Cam Clay (Roscoe, Schofield and Thurairajah, 1963) and the model proposed by Sekiguchi and Ohta (1977) have a sharp corner (vertex) of the yield surface appearing at the effective stress point representing virgin consolidation state in the principal stress space. The corner causes the discontinuity of the gradient of the yield surface; therefore, the stress-strain relationship at this singular point cannot be evaluated by the simple associated flow rule. Special treatment is needed to describe stress-strain relationships at the singular point on the yield surface.
