考虑循环软化特性的饱和软土弹塑性本构关系研究

将软化指数关系与非等向硬化模量场理论相结合，研究了可描述循环荷载作用下饱和软土软化特性的增量弹塑性模型。该模型借助硬化模量的插值和映射中心的移动，在偏应力空间中构造硬化模量的演化规则；通过在弹塑性模量插值函数中引入初始弹塑性模量软化系数，模拟循环荷载作用下软土的刚度软化特性；通过引入硬化模量调整系数，增强循环加载时应力-应变曲线的滞回特性；再通过引入反映应变累积速率和大小的模型参数，描述循环加载时软土的应变累积特性。利用Idriss提出的指数关系式近似拟合软化系数随应力循环次数的变化关系，并通过引入循环应力参数建立了循环软化系数与静应力水平和循环应力水平的关系。阐述了确定模型参数的方法，并利用模型预测了相关试验结果，通过预测结果与试验结果的对比，验证了该模型描述循环荷载作用下软土软化特性的可行性。

Research on elastoplastic constitutive relation for soft clay considering cyclic softening

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.