Abstract: Shanghai 4th layer clay is a typical marine clay with distinct structure. It is helpful for numerical analysis to develop a constitutive model which uses one set of parameters to simulate the mechanical behavior of the clay subject to various stress paths. In this study, the evolution rules of structure and overconsolidation of UNIFIED constitutive model are modified. A new method is proposed to obtain the values of initial state and material parameters of undisturbed soils. In order to verify the modified model, the blocking sampling method is used to obtain undisturbed samples of Shanghai 4th layer clay. The conventional oedometer tests and drained/undrained triaxial compression tests are conducted on the 4th layer clay. A comparison between the test results and constitutive modelling results shows that the modified model and proposed method can simulate the stress-strain behaviors in the oedometer and triaxial tests of 4th layer clay properly, using only one set of parameters. It also shown that the structure of Shanghai 4th layer clay remains stable and the structure remains unchanged even after triaxial shearing at an axial strain of 35%.

Key words: Shanghai clay, constitutive model, triaxial test, structure, overconsolidation