A YIELD FUNCTION AND UNDRAINED BEHAVIOR OF K0 CONSOLIDATED CLAYS

Abstract

The Cam Clay model, now sometimes called the classical model, cannot reproduce strain-softening behavior. The minimum principal effective stress σ₃ constant line for  normally consolidated clay is a straight line with slope three in the space of mean effective stress p and axial differential stress q, which is located inside the yield surface in the Cam Clay model. In other words, there is a region in the Cam Clay model where the stress state of normal consolidation is judged to be over-consolidation. In this study, undrained and drained triaxial compression tests were conducted to clarify the problems of the Cam Clay model described above, and an anisotropic yield function was proposed. Results of the consolidated drained triaxial test showed that the plastic strains occurred when the applied minimum principal stress σ₃ exceeded the past maximum pressure. This result shows that the yield surface for normally consolidated clay is located near the constant line of the minimum principal effective stress. The void ratio of the clay decreased despite the unloading test into the yield surface of the Cam Clay model, which exhibits elastic behavior. This experimental result can emphasize that the stress change in the yield surface causes plastic strain in the clay. The strain softening behavior can be approximated by the proposed yield function if the degree of strain softening is small.