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Study On Permeability Characteristics And Constitutive Relationship Of Structured Soil Based On Soil And Water Characteristic Curve

Posted on:2021-05-23Degree:MasterType:Thesis
Country:ChinaCandidate:Y M ZhangFull Text:PDF
GTID:2370330611497925Subject:Architecture and Civil Engineering
Abstract/Summary:PDF Full Text Request
Soil is a three-phase material composed of soil particles,air and water,and the parameters of soil water movement are the basis of studying the water transfer form in unsaturated soil.Many empirical or theoretical models have been proposed to directly or indirectly predict soil permeability,diffusion coefficient and soil water characteristic curve.Because it is difficult to obtain the diffusion coefficient by experiment,this paper will discuss how to predict the diffusion coefficient accurately and indirectly based on the soil water characteristic curve and permeability.At last,the recommended combination method of soil water characteristic curve model and permeability model suitable for different types of soil samples is given by comparing the predicted diffusion rate of soil samples with the test value by the optimized calculation method.The soil water characteristic curve equation reveals the size and distribution characteristics of soil micro pores or particle gradation.Different particle arrangement and cementation forms not only affect the hydraulic properties of soil,but also lead to softening or dilatation of soil in the stress-strain relationship.In the study of structural soil constitutive model,the main problem is how to explain the structural parameters and their evolution rules.Therefore,this paper will try to use the soil and water characteristic curve equation to explain the structural degradation.The main research methods and contents of this paper are as follows:(1)Based on the grain grading curve of the soil,the reasons for the inconsistency of the change trend of water movement parameters of silty loam,sandy loam and sandy loam in the stage of residual water content are analyzed.In order to accurately predict the diffusivity of silty loam,a new empirical and statistical model of permeability is established by introducing the modified parameters into the existing permeability model.At the same time,a new method is proposed to modify the prediction value of permeability statistical model by using the air entry value.Based on the root mean square error in linear and semi logarithmic coordinates of the predicted diffusivity,a model combination method suitable for different kinds of soil samples is proposed.(2)The different particle arrangement and contact forms of structural soil,overconsolidated soil and cemented soil in microcosmic angle,as well as the influence on their mechanical behavior are analyzed.Based on the modified Cam-Clay model,the non-associated flow rule,structural parameters and their evolution equations are introduced,in which the evolution rule of structural with plastic strain is assumed to be similar to the form of soil water characteristic curve equation.Then,the influence of parameters on soil hardening and softening,shear expansion and shrinkage,and shear strength are analyzed.(3)Finally,a new elastic-plastic constitutive model is used to predict the triaxial drainage test and compression test data of artificially improved sand and natural structural soil.The results of model fitting parameters are compared with the real physical properties of soil samples and the analysis rules of model parameters to verify the validity and accuracy of the new constitutive model in the verification of structural soil mechanical behavior.
Keywords/Search Tags:soil water characteristic curve, hydraulic conductivity, diffusivity, structured soil, constitutive model
PDF Full Text Request
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