超固结因素影响下桩柱结构地震响应

Seismic response of piles structure under overconsolidation

地震荷载作用下饱和地基的循环加载响应以及动力液化问题成为地震工程研究中的重要课题。为更好研究饱和地基在考虑超固结因素下的影响及其在循环加载下的演化规律,在下负荷面剑桥模型理论框架下分别通过排水和非排水三轴压缩试验对循环加载下土体的加载响应进行数值模拟研究。在以上研究基础上,基于ADINA81平台开发负荷面剑桥模型本构关系模块,建立两相饱和地基下的桩-土耦合体系的动力非线性有限元数值模型,对不同模型下桩柱结构的地震响应进行了数值模拟对比研究。研究发现在下负荷面剑桥模型下结构的动力响应数值模拟结果介于弹性模型与经典剑桥模型之间,考虑超固结因素影响后,地基表现出更好的抗液化特性与更高的承载能力,能改善结构的动力响应与受力状况。

In view of the complex nonlinearity of soil medium,particularly considering the great influence of strength degradation of saturated foundation soil under earthquake incident,the study of cyclic loading response and the mechanics of cyclic liquefaction of soil has been known as one of the most important issues in the seismic research and design of civil engineering structures.Considering that normally consolidated soil turns into overconsolidated state once experiencing stress unloading in cyclic loading,which has great influence on the mechanical properties of soil in turn,and in order to investigate the effect of overconsolidation factor and the corresponding evolution of over?consolidation ratio(OCR)under cyclic loading,comparative numerical simulation studies are carried out through both drained and undrained triaxial compression tests based on the subloading surface Cam?clay model.The stress?strain relationship,compressibility and the development of excess pore water pressure are studied in detail.The comparative test results show that with the consideration of overconsolidation factor into the classical Cam?clay model,the yield strength,as well as the corresponding liquefaction resistance of soil,is improved significantly.Based on the comparative study of overconsolidated soil??s mechanical properties and liquefaction resistance,a dynamic nonlinear FEM model of pile?soil coupled system with saturated soil foundation is established based on the program of ADINA81along with the development of constitutive module of the subloading surface Cam?clay model,and the comparative study of the seismic response of pile structure is carried out with different constitutive models.Simulation results show that the seismic response derived from the subloading surface Cam?clay model lies between classical Cam?clay model and linear elastic model.Through the comparison,it can be concluded that by taking the influence of overconsolidation factor into consideration,the foundation soil demonstrates better liquefaction resistance and bearing capacity,and thereby affects the corresponding seismic response and force conditions of the structure.