Abstract: An incremental elastoplastic constitutive model describing the softening of soft clays subjected to cyclic loading is proposed by combining the softening exponential relationship with non-isotropic hardening modulus field theory. The evolution rule of hardening modulus field is established with the interpolation of hardening modulus and the mobile mapping center in the deviatoric stress space for the model. The stiffness softening of soft clays with cyclic loading is simulated with a softening coefficient of initial elastoplastic modulus in the elastoplastic modulus interpolation function for the model. Hysteretic loops of stress-strain curves are enhanced with a parameter adjusting hardening modulus for the model. Cyclic accumulative strains of soft clays subjected to cyclic loading are described by introducing a parameter to take into account the rate and the level of accumulative strains for the model. Relation curves of cyclic softening coefficient and the number of stress cycles are fitted with the exponential equation proposed by Idriss. Besides, the relationships among cyclic softening coefficient and static stress level and cyclic stress level are established by introducing a cyclic stress parameter. The methods for determining model parameters are also presented. The predicted results are obtained with the model. Comparing the predicted results with test results, it is verified that the model can describe the softening of soft clay subjected to cyclic loading.

Key words: soft clay, cyclic softening, constitutive model, cyclic elastoplasticity, hardening modulus field