Research On The Anisotropic Constitutive Model Of Overconsolidated Natural Soft Clay

Natural soft clay often brings many difficulties and troubles to engineering practice due to its complex mechanical properties.Therefore,the research on its deformation and strength characteristics has become a hot issue in the field of soil mechanics.The soft clay in natural state usually has obvious anisotropy and structure which affected by sedimentation and consolidation.In addition,the stress history of soil also have an important impact on its mechanical properties.In practical engineering,soft clay is often in a state of overconsolidated under the complex stress path such as unloading and reloading.Therefore,it is of great significance to increase the consideration of overconsolidated characteristics of soft clay in the constitutive model.In view of this,on the basis of previous work,this paper systematically studies the plastic anisotropy,overconsolidated characteristics and structural yield characteristics of natural soft clay from three aspects of law analysis,theoretical derivation and mathematical modeling,and establishes an anisotropic elastic-plastic model of overconsolidated natural soft clay considering cyclic loading characteristics.The major substance and achievements of this dissertation can be concluded as follows:1.Based on the existing literature,the previous research achievements on the anisotropy,overconsolidation and structure of soft clay and their influence on the engineering properties are briefly summarized.On this basis,the research progress of constitutive model considering the anisotropy,overconsolidation,structure and cyclic loading characteristics of soft clay is comprehensively summarized and analyzed,thus the main thought of this paper is clarified.2.The critical state theory of soft clay and the characteristics of traditional critical state model based on it are briefly introduced.While making a brief comment on this kind of model,the superloading and subloading yield surface theories are recommended in view of its shortcomings,and the constitutive equation of the modified Cambridge model with superloading and subloading yield surface is derived,which lays a theoretical foundation for the establishment of the subsequent model in this paper.3.An anisotropic subloading yield surface model for normally consolidated and overconsolidated of remolded soft clay is established.Based on the modified Cambridge model with isotropic subloading yield surface,referring to Shen Kailun’s(2006)method of describing anisotropy,the anisotropic state variable and rotation hardening law are introduced while using the anisotropic yield surface to comprehensively consider the initial anisotropy and stress-induced anisotropy of soil;the non isotropic hardening law proposed by Coliins et al(2002)is introduced,which are unified with rotation hardening law and overconsolidation state variables in the elastic-plastic model with subloading yield surface using the associated flow rule.After a detailed analysis of the model parameters,the rationality and effectiveness of the model are fully verified by simulation of multiple groups of soft clay test results and comparison with other models.4.An elastic-plastic model with superloading and subloading yiled surfaces of natural soft clay under static and dynamic loads is established.According to the established anisotropic subloading yield surface model of remolded soft clay,which can not reasonably describe the structural properties of natural soft clay and some of its mechanical properties under the condition of alternating load,referring to the method of describing structural properties by Zhang et al(2007),the evolution method of structural state variables is improved;At the same time,the simulation of cyclic loading is realized in the program,with the emphasis on the study of cyclic loading The cumulative strain characteristics of natural soft clay under cyclic loading.The model can comprehensively consider the anisotropy and structure of natural soft clay under cyclic load.The validity of the model is preliminarily verified by the simulation calculation of relevant tests and comparison with other models.