Experimental Research On Nonlinear Rheological Characteristics Of Expansive Soil

Expansive soil is a kind of multi-fissures, water swelling, dehydration shrinking soil formed in the natural geological processes, it has significant swell-shrink characteristics. It is one kind of disastrous soft soil has the obvious rehological properties. Therefore, carry out research on the nonlinear rheological characteristics of expansive soil, discuss its constitutive relationship considering time factors, research its mechanical parameters and compression creep characteristics, construct the corresponding empirical model, these has important theoretic value and practical significance in developing the research scope of expansive soil, revealing the internal law of its rheology, guiding its engineering practice and preventing the engineering accident. For this reason, the research on the nonlinear rheological characteristics of this soil is carried out in this thesis based on the comprehensive analysis of the domestic and international research in this field. The research is funded by the National Natural Science Funds(No:50978097), the Hunan Province Natural Science Funds(No:08JJ3092) and the Science and Technology Department of Hunan Province Funds(No:2010SK3047). Combining compression creep tests, direct shear creep tests with theoretical analysis and numerical analysis methods, a series of in-depth theoretical and experimental researches on nonlinear rheological characteristics of expansive soil are carried out. Some conclusions and research achievement are obtained as follows.(1) Experimental research on compression creep:①Through the compression creep tests and loading-unloading compression rebound creep tests, the deformation rules and patterns of Nanning unsaturated expansive soil were discussed in the compressed creep process. The compression creep of this soil showed two-stage attenuation stable, there was no accelerated creep even at higher stress levels. With the increase of stress level, creep deformation increased and creep curves showed similar development. With the increase of water content, creep deformation increased and creep curves showed similar development either.②ccording to the results of loading-unloading compression rebound creep tests, the compression creep deformation components of the soil contained elastic, plastic and viscoelastic deformation component. Based on this analysis, the relevant compression-creep model and equation were obtained.③Through the analysis of compression creep component models, a method for determining the compression rheological parameters was put forward. Based on that, the nonlinear compression rheological characteristics of this soil were studied, and relevant nonlinear model theory and analysis method were proposed.(2) Experimental research on shear creep:①Through the shear creep tests and loading-unloading shear rebound creep tests, the deformation rules and patterns of Nanning unsaturated expansive soil were discussed in the shear creep process. At lower stress level, the shear creep of this soil showed two-stage attenuation stable. At higher stress level, the shear creep showed three-stage creep characteristics, and eventually the shear failure of the soil occurred because of the accelerated creep.②In this thesis, the relationship of the shear creep characteristics to water content and vertical stress level was discussed. With higher water content, the shear creep characteristics of this soil was more obvious. At lower vertical stress level, the shear creep characteristics of this soil was more obvious either.③According to the results of loading-unloading shear rebound creep tests, the shear creep deformation components of the soil contained elastic, plastic and viscoelastic deformation component. Based on this analysis, the relevant shear-creep model and equation were obtained.④Through the analysis of shear creep component models, a method for determining the shear rheological parameters was put forward. Based on that, the nonlinear shear rheological characteristics of this soil were studied, and relevant nonlinear model theory and analysis method were proposed.(3) Research on nonlinear experiential rheological modelBased on the experiential model methods and half-theoretics half-experience model methods, the experiential and the half-theoretics half-experience rheological constitutive models were established separately. Both models can reflect the nonlinear rheological characteristics of unsaturated expansive soil commendably. In engineering practice, those models provids a theoretical basis for the calculation on nonlinear rheological characteristics of this soil. (4) Research on long-term strength of unsaturated expansive soilBased on the direct shear creep test results, the direct method was used to analysis the shearing stress-strain equivalent time curves. The long-term strength of unsaturated expansive soil under different vertical stress was discussed. A method for determining the long-term strength of the soil was put forward.(5) Numerical analysis on rheological characteristics of unsaturated expansive soil.On the basis of rheological model and constitutive equation, the relevant numerical analysis method was put forward. According to the numerical analysis, the correctness of theoretical model and experiential model was verified, and related rheological parameters were discussed.