考虑各向异性影响的循环弹塑性模型

Cyclic elasto-plastic constitutive model considering anisotropic effect

软黏土在动荷载作用下具有显著的非线性、滞回性和变形累积性等动力特性,因此采用弹塑性模型来描述土的动应力应变关系更为合理。基于混合硬化塑性模量场理论,建立了一个总应力形式的、屈服面连续变化的饱和黏土不排水增量弹塑性动本构模型。模型克服了一般嵌套塑性模型因在模量场中存在共轭点而具有奇异性的不足,不需要记忆应力反向面,也不需要判断当前屈服面是否超过应力反向面进而引入零圆心位置的过渡应力反向面,极大地简化了模型和数值计算。由于现有弹塑性动本构模型通常不能考虑各向异性固结对土体变形和破坏的影响,通过在破坏面方程中引入各向异性偏应力张量来反映各向异性的影响。对试样动三轴试验的结果与文献模型计算结果的对比分析表明:模型能够合理地描述土的主要动力特性及应力诱发各向异性对土体变形和破坏的影响。

Soft clay was magnificently nonlinear, hysteretic and accumulatively deformable under dynamic load, and therefore it was more reasonable to describe its stress-strain relation with elasto-plastic models. Based on the mixed hardening plastic modulus field theory, an incremental elasto-plastic dynamic constitutive model for the saturated clay under the undrained condition, expressed in the form of total stress, was developed. Its yield surface continuously varied. The model overcame the defect that there was conjugate point thus singularity in plastic modulus field in the nested yield surface model. In addition, the model didn＇t need to remember the stress inverse surface and to judge whether the current yield surface exceeded the stress inverse surface. Owing to that the existing elasto-plastic dynamic model was unable to consider the effect of anisotropic consolidation on soil deformation and failure, so it was attempted in this paper to reflect this effect by introducing an anisotropic deviatoric tensor of stress in the failure surface equation. The predicted stress-strain relation of soil was compared with the test and the calculated results of existing model. It is shown that the proposed model could depict the primary soil dynamic characteristics and the effect of anisotropic consolidation on soil deformation and failure.