人工冻土黏弹塑性本构参数反分析研究

通过大量的人工冻结黏土蠕变试验研究，获得在高偏应力下人工冻结黏土具有显著的蠕变特性：当应力水平较低时，人工冻土发生黏弹性蠕变变性；当应力水平较高时，人工冻土发生黏塑性蠕变变性。因此，以西原模型为基础，增加一个黏弹性元件项和用抛物线屈服函数代替塑性屈服项，构建了高应力下抛物线型黏弹塑性蠕变本构模型。改进的西原模型可以较好描述人工冻土剪切蠕变特性。基于小生境技术的遗传算法和人工冻土黏弹塑性模型有限元理论，在FEPG（有限元程序生成器）自动生成平台上研发了位移反分析程序。利用现场实测数据对深井冻结井筒开挖过程进行了位移反分析，获得了与试验相一致的冻土本构力学模型参数，数值分析结果与实测数据之间的误差在6%以内，反演结果验证了模型的可行性。冻结井筒开挖过程的位移反分析获得的人工冻土本构模型参数，能反映冻结壁施工过程和有效冻结范围内冻土本构参数平均值，因而具有广泛的代表性，对冻结壁应力场、位移场和稳定性预测具有重要工程意义。

Back analysis of viscoelasto-plastic constitutive parameters of artificial frozen soil

By lots of creep test researches, artificial frozen clay shows an obvious creep behavior under high deviatoric stress. When artificial frozen clay in low stress level, a viscoelastic creep deformation presents. While in high stress level, viscoplastic creep deformation presents. On the basis of Nishihara model, parabolic viscoelasto-plastic creep constitutive model is constructed by adding a viscoelastic element and parabolic yield function instead of plastic yield. The modified Nishihara model can describe the shear creep characteristics of artificial frozen soil well. Based on niche technology, genetic algorithm and viscoelasto-plastic theory, the model of viscoelasto-plastic displacement back analysis for artificial frozen soil has been set up by finite element program generator (FEPG). With the measured data, displacement back analysis is conducted during the excavation of deep freezing shaft. And the obtained parameters of mechanical model for frozen soil agree with the test results. The deviation between numerical calculation results and measured data is less than 6%; so the inversion results verify the feasibility of the model. The constitutive model parameters, which obtained by displacement back analysis for artificial frozen soil, can reflect the average of frozen wall construction process and effective freezing range. So it has wide representation and important engineering significance for frozen wall stress field, displacement field and stability prediction.