Study On Creep Properties And Nonlinear Creep Constitutive Model Of Chengdu Clay

Chengdu Clay is widely distributed in the west of Sichuan Basin,the northwest hilly and high order,mainly brown yellow and brown red,with high water content,compressibility,low strength and strong structure and so on.Under the action of long-term load,Chengdu Clay will have obvious creep phenomenon,which will adversely affect the stability of foundation Pit Engineering,Subgrade Engineering and slope Engineering.Therefore,it is of great theoretical value and engineering significance to study the creep properties of Chengdu Clay and to construct a nonlinear creep constitutive model for Chengdu Clay.Because the geological condition and the material composition of Chengdu Clay are different with the regional differences,the nature of the soil will vary.Taking the clay of a foundation pit in Chengdu Imperial Longshan as an example,the experimental study of mechanical properties and creep characteristics of Chengdu Clay was carried out,and the unsteady characteristics of creep curve,long-term strength,elastic modulus and viscous coefficient of Chengdu Clay were analyzed emphatically.The nonlinear empirical creep model,nonlinear semi theoretical empirical creep model and fractional derivative unsteady creep model are constructed by different methods,and the characteristics of each model parameter are analyzed,and the applicability,scientific rationality and superiority of each creep model are analyzed by fitting verification.The main research of this paper is as follows:(1)The basic physical and mechanical properties of clay in Longshan and Luo belt were analyzed by on-site clay sampling and laboratory geotechnical tests.The failure stress of Chengdu clay under different water content and confining pressure is obtained,and the plasticity Index and liquid index are larger and the gradation is better.It lays a foundation for the Creep Test and analysis of Chengdu Clay.(2)Through triaxial consolidation undrained creep test,the characteristics of creep test curve,long term strength,elastic modulus and viscous coefficient of the clay in the Longshan and the Luo and Yu are analyzed,and the unsteady characteristics of elastic modulus and viscous coefficient of clay are clarified.It lays a foundation for the construction of nonlinear creep constitutive model of Chengdu Clay.(3)When constructing nonlinear creep model,according to the characteristics of creep curve,the nonlinear relationship between stress-strain and strain-time is established,and the nonlinear empirical creep constitutive model is constructed according to the similarity principle of creep curve.The creep deformation of Chengdu Clay is divided into two parts: linear and nonlinear,and the model is respectively determined,Based on the unified theory of creep deformation,a nonlinear semi theoretical empirical creep constitutive model is constructed.On the basis of fractional derivative viscous element,the fractional derivative unsteady creep constitutive model is constructed by constructing the instantaneous elastic model of fractional order,viscoelastic model and viscoelastic-plastic model,and considering the unsteady behavior of elastic modulus and viscous coefficient.(4)The characteristics of the parameters in each nonlinear creep model are analyzed,the influence of the parameters on creep behavior of Chengdu Clay is obtained.At the same time,the nonlinear empirical creep model is only suitable for the decay creep stage by fitting and verifying the creep test of Chengdu Clay.Semi-theoretical empirical creep model and fractional derivative creep model are suitable for the whole creep process,in particular,the latter has obvious advantages to the description of accelerated creep,and it is proved that it is necessary to consider the unsteady behavior of elastic modulus and viscous coefficient in the nonlinear creep model.Through the analysis of parameter characteristic and fitting verification,the applicability,scientific rationality and superiority of the constructed nonlinear creep constitutive model are demonstrated.In this paper,the creep characteristics of Chengdu Clay are studied emphatically,and the changes of clay properties in creep process are analyzed,and three new nonlinear creep constitutive models are constructed,and the parameter characteristics of the model are analyzed,and the applicability and scientific rationality of the model are verified.It provides a reference for the foundation engineering design and construction design of Chengdu Clay area.At the same time,the research scope of the Creep property of Chengdu Clay is widened,which lays a foundation for the study of creep properties of Chengdu Clay.Therefore,the research of this paper has important research value and engineering significance.