Research On Constitutive Model Of Creep Properties And Anisotropy Of Natural Soft Clay

Natural saturated soft clay with very complicated mechanics behavior has brought great difficulties to engineering practice and has always been an important direction in geotechnical engineering.In addition to its structural and anisotropic properties,naturally saturated soft clays also have creep characteristics that make the structure of buildings still surprisingly deform or even collapse after it is put into operation.However,at present,no matter at home or abroad,the experimental research and theoretical research results in this aspect are still few,and need further enriched and improved.In view of this,on the basis of the previous studies on the creep test and theoretical research of soft clay,this paper systematically studied the deformation of natural saturated soft clay subjected to static and dynamic loads,and proposed an anisotropic elastic-visco-plastic bounding surface model for structural soft clay,which can describe creep characteristics and cyclic loading properties.The main research contents of this article are as follows:1.Through reviewing a large amount of literature,we summarized the research results of the former on the structural,anisotropic and creep properties of soft clay and their impact on the engineering properties.On this basis,the existing constitutive models which can considerate structural,anisotropic,creep and cyclic loading characteristics,were analyzed.2.The critical state theory based on remolding soft clay and the critical state model were introduced.The deficiencies of critical stade model in the description of certain properties of natural soil were analyzed,and the new idea of boundary surface theory was introduced.This paper briefly introduced the boundary surface theory and models,and layed a theoretical foundation for the establishment of the boundary surface model of this paper.3.An anisotropic elasto-visco-plastic boundary surface model was established to consider the creep properties of natural structural soft clay under static loading.This model is based on the concept of natural structural and anisotropic boundary surface models established by the predecessors.By introducing the concept of lagging deformation,the structural damage evolution rule and the anisotropic rotation hardening law are revised.Combined with the modified rotational harding rule and degradation law,the law of isotropic hardening are unified with the boundary surface formulation using associated flow laws.Through the simulation of multiple sets of indoor triaxial creep test results,the reliability of the proposed model was verified.4.Based on the research in the third chapter of this paper,an elasto-visco-plastic boundary surface model that can consider cyclic creep and cyclic-creep coupling characters was established by improving the mapping law.The model adopts the movable mapping center when considering the cyclic loading,integrates the loading and unloading process into a loading process during the cyclic loading process,and introduces the concept of lagging deformation so that it can consider not only the creep but also the cyclic loading characteristics.At the same time,the cycle-creep coupling characteristics can be considered in the proposed models.The cyclic three-axis undrained creep tests of Wenzhou saturated soft clay and Shanghai grey silty clay were simulated to verify its accuracy.