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Research on the Disturbed State Constitutive Model of the Structural Loess and Application

Author: XuYaLi
Tutor: LiuZengRong
School: Xi'an University of Architecture and Technology
Course: Geotechnical Engineering
Keywords: loess structure constitutive model conventional triaxial test numericalsimulation mechanical model disturbed state concept theory disturbancefunction
CLC: TU444
Type: Master's thesis
Year: 2011
Downloads: 114
Quote: 1
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Abstract


With the deep develop and the gradual promotion of western development strategy,various construction projects in northwest china have been in full swing. The projectalso has been developing increasingly towards the direction of large-scale,exceedingstandard and more complex conditions, which will lead to higher requirements for themechanical model and the reliability and accuracy of the calculation method of soil. Sothis has very important theoretical and practical significance for research on themechanical characteristics of loess and the constitutive relation of loess.On the basis of the summarizing and deriving the study results of the seniors, andthrough the research works including meticulous experimental research, precisetheoretic derivations and reasonable numerical analysis, some achievements which havecertain theoretical value and actual significance are obtained.Firstly, according to the connection and arrangement characteristics of loessparticles, a series of laboratory experimental research for revealing the structuralproperties of loess and the evolution law of the disturbance function are carried out.According to the characteristics of loess such as soil macropore and overheadstructure and mosaic structure and the fact that the cementing material at particlecontacting point is soluble salt, the compressive property and the compression-resilienceproperty and the resilience-compression property of intact loess and remolded loessunder five kinds of different water content are researched through the confinedcompression test. The influence of water content on the connection characteristics andarrangement characteristics of loess particle and the characteristics of the disturbed stateof loess structure is discussed deeply. And based on the triaxial compression test, thestress-strain relationship and the relationship of volumetric change and strain and theshear strength parameters under the conditions of four kinds of confining pressure and five kinds of water content are researched and the influence of confining pressure andwater content on strength and deformation and the structure of loess is discussed. Theseresearch results provide test basis for further research on the evolution law ofdisturbance factor under one dimensional stress state and three-dimensional stress states,the influence of water content and confining pressure on disturbance functionparameters, the construction of the disturbed state constitutive model of structural loessand microscopic numerical simulations.Secondly, the researches on microscopic numerical simulations are carried out inorder to reveal the structural properties and characteristics of the disturbed state.Based on the method of the particle flow, the microscopic numerical simulations ofthe structural property of loess are carried out, by changing three different microscopicparameters such as the initial normal contact stiffness between particles, the initialtangential contact stiffness, friction coefficient and porosity and so on, the influence ofthe coupling characteristics and arrangement characteristics of loess particle on strengthand deformation is discussed, the relation between the microscopic particle contact,friction, coupling, arrangement and macro test results is established, and the internalevolution mechanism between disturbed state and loess structural property is furtherrevealed, which it provides the basis for constructing the disturbed state constitutivemodel in the macroscopic mechanical terms.Thirdly, a new method to ascertain preconsolidation pressure of intact loess isproposed, the influence of water content on structured yield stress andpreconsolidation pressure and structural strength is further analyzed.According to the difference of the indoor and in situ compression test, andconsidering of the sampling disturbance, by eliminating the influence of structuralstrength, by using the thought that the compression curves of remoulded soil arereduced the compression curves of undisturbed soil, a new method to ascertainpreconsolidation pressure of intact loess is proposed, which provides a kind of newthought for judging the soil consolidation state correctly. It is compilied the program torealize the Casagrande method by Matlab software, and the influence of water contenton structured yield stress and preconsolidation pressure and structural strength is furtheranalyzed.Fourthly, the disturbance function is defined, which regard the void ratio asparametric variable, the one-dimensional disturbed state compression model of thestructural loess is constructed.Based on the disturbed state theory, and combined with the influence of the structural property on compression properties, the disturbance function is defined,which regard the void ratio as parametric variable, the evolution law of the disturbancefunction is researched, the influence of water content on the disturbance function isanalyzed, the one-dimensional disturbed state compression model of structural loess isconstructed and verified.Fifthly, the single parameter disturbance function is proposed, which take thesecant modulus as parametric variable, and the double parameters disturbance functionis proposed, which take the bulk modulus and the shear modulus as parametric variablerespectively, the disturbed state constitutive model of loess under the three-dimensionalstress states is constructed.Based on the disturbed state theory,and combined with the characteristics ofstress-strain relationship of intact loess and remolded loess, the single parameterdisturbance function is proposed, which take the secant modulus as parametric variable.And the double parameters disturbance function is proposed, which take the bulkmodulus and the shear modulus as parametric variable respectively, and the evolutionlaw of both kinds of the disturbance function are researched, the influence of watercontent and confining pressure on parameters of the disturbance function is discussed.Based on the research on the evolution law of the double parameters disturbancefunction, the disturbance state constitutive model of loess is established, it can bedegenerated into the modified Cam-clay model under certain conditions.Sixthly, based on the second development function of the ABAQUS software, thesubroutine of the disturbed state constitutive model of structural loess is developed, andthe feasibility and rationality of the model are verified through experiments andexamples.Based on the second development platform of ABAQUS software, the subroutineof the disturbed state constitutive model of structural loess is developed, and the validityand feasibility of the model are verified through experiments. Through the numerricalsimulation on the model test of pile group foundation in loess area, the calculationresults of this model and the modified Cam-clay model are analyzed constrastively, thereasonableness and superiority of the disturbed state constitutive model of structuralloess are confirmed.

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CLC: > Industrial Technology > Building Science > Soil mechanics,foundation engineering > Various types of soil and foundation > Loess and foundation
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