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Study on Triaxial Creep Characteristics of Loess

Author: LiGuangDong
Tutor: LuoYaSheng
School: Northwest University of Science and Technology
Course: Geotechnical Engineering
Keywords: Loess experiences creep model components creep model Viscosity coefficient
CLC: TU411
Type: Master's thesis
Year: 2011
Downloads: 37
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Abstract


With the development of the west regions, an increasing number of projects relate to loess, due to its extensive distribution, to guarantee the projects unfolded on loess plateau being operated safely, deep researches on the creep property of loess are highly instructive both theoretically and practically to engineering construction on plateau areas.In this thesis, the loess of Wugong area in Shaanxi province is put to use. By a series of experiments on the creep property of undisturbed and reconstituted loess based on drained and undrained triaxial creep tests, can conclude that factors like deviatoric stress, dry density, confining pressure, and moisture content influence the creep property of loess, and by contrasting how drainage condition affects the creep property of loess, model an experimental formulas on loess in this area. The relationship between the viscosity and stess and strain is also analyzedThe main findings of this thesis include:(1) When deviatoric stress is weak, weakening creep takes place, with the strengthening of the stress, at first, weakening creep appears, and then steady creep; if more force is added, accelerating creep happens, and sample is destroyed soon. The lower the dry density and confining pressure is, the higher the moisture content is, the bigger the creep deformation is, and it takes longer to reach stabilization. Under the same conditions, the creep deformation of saturated remolding sample is larger than that of remolding sample with natural water content than that of undisturbed soil sample with natural water content. It is also true of the time taken to reach stabilization. When deviatoric stress is weak, the deformation is more under the drained condition than under undrained condition, However, with the stress being enhanced to a certain level, under the undrained condition, the strain gets stronger with the development of time, even the sample’s destruction may happen, on the other side, under the drained condition, the deformation of the sample arrives at stabilization after a period of accelerating creep.(2) Under the undrained condition, the curves of stress-strain ratios of Q3 loess are similar, and show a typical characteristic of nonlinearity. The nonlinearities reinforce with the time and the stress. When the stress is less than the yield stress, the loess is considered as a linear viscoelastic layer, and when the stress is more than the yield stress, the loess is considered as a nonlinear viscoelastic layer. With the increasing of dry density and confining pressure, the strain of the loess gets stronger. But With the increasing of moisture content, the strain of the loess gets weaker. And the curves of stress-strain ratios under the drained condition are approximated by similar straight lines.(3) Based on mathematical statistic method, establishes a suitable for the region loess experience model, using hyperbolic function to describe the relationship of strain-time, and using exponential function to describe the stress-strain relationship. It also analyzes the model parameters and confining pressure relationship, confining pressure also considered by this model, with comparison traditional Singh - Mitchell creep model and of Mesri creep model, this paper the model is more accurate. This model can be used to describe the undrained and drainage condition creep process. But creep model parameters sizes are not the same.(4) In this paper, chose the burgers component model to fit the date of experiment. It’s consistent with the test date. And analyzes the relationship four parameters and partial stress, confining pressure, EM、EK、ηMparameters is decrease with the deviatoric stress’s increase, butηK parameters is increase. These four parameters are increase with the confining pressure’s increase(5)Based on the analysis of the experimental data, deduced the relation viscous coefficient and time, partial stress, confining pressure, and verifying the rationality of the relationship

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