动力UH模型及其有限元应用

饱和砂土在循环载荷下具有复杂的应力应变关系, 通常表现出液化过程中的大变形以及往返活动性现象. 为简单有效地模拟上述特性, 在超固结UH模型的基础上, 将其扩展为可考虑砂土动力加载下的本构模型. 具体做法有3点: (1)改变屈服面椭圆长短轴之比, 将比值定义为反映应力诱导各向异性转轴斜率的函数; (2)引入旋转硬化规则, 用来反映应力诱导各向异性; (3)建立一个与旋转硬化规则以及临界状态特性相协调的统一硬化参数. 模型预测结果表明, 所提动力模型可简单、有效地用于砂土在动力载荷下应力应变关系的模拟. 最后将该动力UH模型嵌入到有限元软件中, 三维地基的动力加载模拟结果表明, 动力UH模型可方便地应用于岩土工程实践中. 

DYNAMIC UH MODEL FOR SANDS AND ITS APPLICATION IN FEM

Complex stress-strain relationship is exhibited for saturated sands under cyclic loading conditions. The large deformation and phenomena of cyclic mobility occur during liquefaction.In order to simulate the above mechanical behaviors of sands simply and effectively,a dynamic constitutive model which can be used to describe stress-strain relationship for sands under dynamic loading conditions is proposed on the basis of the UH model for overconsolidated clay.There are three specific revisions in this paper:(1) Ratio between the length of long axis to that of short axis for ellipse yielding surface is defined as the function for slope of rotational axis which can be used to reflect stress-induced anisotropy.(2) Rotational hardening rule is introduced into the proposed model to reflect stress-induced anisotropy.(3) A unified hardening parameter is established by coordinating rotational hardening rule and critical state behavior.Comparison between model prediction and test results demonstrates that the proposed model can be conveniently used to simulate stress-strain relationship under dynamic loading conditions for sands.Dynamic constitutive model is also embedded into FEM program. Stress-strain relationship of sands for soils foundation is simulated.Simulated results have shown that the proposed model can be applied into geotechnical engineering practice conveniently.