福建标准砂加筋硬化与循环累积变形三轴试验及本构模型
发布时间：2018-12-24 13:02
【摘要】：土的本构关系以土的应力应变规律作为研究对象,是岩土工程学科的重要理论基础,为岩土工程的分析和设计提供理论依据和指导。砂性土在我国有着广泛的分布,针对其基本的力学特性,国内外的学者已开展了许多相关的研究,建立了各种各样的本构模型。近几十年,许多新型的水利电力工程、高层建筑和交通工程如雨后春笋,同时也带来了许多新的岩土工程问题,如砂土的纤维加筋硬化问题和循环累积变形问题。福建标准砂是我国的一种代表性试验用砂,本文针对砂土的纤维加筋硬化问题和循环累积变形问题,开展了一系列福建标准砂静动力三轴试验,研究了福建标准砂的纤维加筋和循环累积变形特性,并在此基础上分别建立了相关的砂土本构模型。 纤维加筋是一种新型的土体改良技术,建立纤维加筋土的应力应变关系及相关的力学模型,不仅有利于纤维加筋土强度和变形特性的预测,而且也能为纤维加筋土的工程设计提供参考依据。而目前纤维加筋土的力学模型及计算理论研究一直是该领域的研究弱项。本文将纤维加筋土考虑为基本相和纤维相的组合体,分别采用修正剑桥模型和线弹性模型,考虑了大应变时纤维加筋土的屈服,引入了加筋土的合理强度模型作为破坏准则,从而建立了纤维加筋土的一种两相本构模型。同时,开展了纤维体积含量为1%的加筋砂的三轴固结排水剪切试验,对该两相本构模型进行了验证。 近几年,近海风电产业的发展十分迅速。海上风电机组基础经常受到风、波浪、水流甚至地震等循环荷载的作用。长期的循环往复荷载的作用下,基础往往会产生循环累积变形,从而影响到海上风电机组的正常运行。本文开展了一系列饱和砂土的排水条件单向循环三轴压缩和拉伸试验,研究了动应力水平、初始平均应力、初始静应力比、初始密实度对福建标准砂的循环累积变形特性的影响,发现动应力、初始平均应力和初始静应力比越大,初始密实度越小,砂土的循环累积变形越大。之后对循环三轴试验的数据进行了分析,得到了轴向循环累积应变和循环次数之间的双对数线性关系,将所有影响因素包含于第一次轴向循环累积应变。分析了第一次轴向循环累积应变与初始平均应力和偏应力水平之间的关系。最后基于合理的软黏土循环累积变形计算模型,对其中的偏应力水平的定义进行了适当地修正,并引入与密实度相关的砂土抗剪强度理论,建立了饱和砂土的循环累积变形显式计算模型,并利用循环三轴试验的数据对其进行了验证。
[Abstract]:The constitutive relation of soil takes the stress-strain law of soil as the object of study. It is an important theoretical basis of geotechnical engineering and provides theoretical basis and guidance for the analysis and design of geotechnical engineering. Sand soils are widely distributed in China. According to their basic mechanical properties, scholars at home and abroad have carried out many related studies and established various constitutive models. In recent decades, many new water conservancy and electric power projects, high-rise buildings and traffic projects have sprung up, at the same time, many new geotechnical engineering problems have been brought, such as fiber reinforced hardening of sand and cyclic cumulative deformation. Fujian standard sand is a representative test sand in China. A series of static and dynamic triaxial tests of Fujian standard sand have been carried out in this paper, aiming at the problem of fiber reinforced hardening and cyclic cumulative deformation of sand. The properties of fiber reinforcement and cyclic cumulative deformation of Fujian standard sand were studied. Fiber reinforced soil is a new soil improvement technology. The establishment of stress-strain relationship and related mechanical model of fiber reinforced soil is not only beneficial to predict the strength and deformation characteristics of fiber reinforced soil. It can also provide reference for the engineering design of fiber reinforced soil. At present, the research on mechanical model and calculation theory of fiber reinforced soil is always weak in this field. In this paper, the fiber reinforced soil is considered as the combination of basic phase and fiber phase. The modified Cambridge model and the linear elastic model are used to consider the yield of the fiber reinforced soil when the strain is large, and the reasonable strength model of the reinforced soil is introduced as the failure criterion. Thus a two-phase constitutive model of fiber reinforced soil is established. At the same time, the triaxial consolidation and drainage shear tests of reinforced sand with fiber volume of 1% were carried out, and the two-phase constitutive model was verified. In recent years, offshore wind power industry is developing very rapidly. The foundation of offshore wind turbine is often subjected to cyclic loads such as wind, wave, current and even earthquake. Under the action of long term cyclic reciprocating load, the foundation will often produce cyclic cumulative deformation, which will affect the normal operation of offshore wind turbine. In this paper, a series of unidirectional cyclic triaxial compression and tensile tests of saturated sand have been carried out. The dynamic stress level, initial average stress and initial static stress ratio have been studied. The effect of initial compactness on cyclic cumulative deformation of Fujian standard sand shows that the larger the ratio of dynamic stress, initial mean stress and initial static stress, the smaller the initial compactness, the greater the cyclic cumulative deformation of sand. Then, the data of cyclic triaxial test are analyzed, and the logarithmic linear relationship between axial cyclic cumulative strain and cyclic number is obtained, and all the influencing factors are included in the first axial cyclic cumulative strain. The relationship between the first axial cyclic cumulative strain and the initial average stress and deflection stress level is analyzed. Finally, based on the reasonable calculation model of cyclic cumulative deformation of soft clay, the definition of deflection stress level is modified appropriately, and the theory of sand shear strength related to compactness is introduced. An explicit model of cyclic cumulative deformation of saturated sand is established and verified by cyclic triaxial test.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU411;TU441
本文编号：2390659
[Abstract]:The constitutive relation of soil takes the stress-strain law of soil as the object of study. It is an important theoretical basis of geotechnical engineering and provides theoretical basis and guidance for the analysis and design of geotechnical engineering. Sand soils are widely distributed in China. According to their basic mechanical properties, scholars at home and abroad have carried out many related studies and established various constitutive models. In recent decades, many new water conservancy and electric power projects, high-rise buildings and traffic projects have sprung up, at the same time, many new geotechnical engineering problems have been brought, such as fiber reinforced hardening of sand and cyclic cumulative deformation. Fujian standard sand is a representative test sand in China. A series of static and dynamic triaxial tests of Fujian standard sand have been carried out in this paper, aiming at the problem of fiber reinforced hardening and cyclic cumulative deformation of sand. The properties of fiber reinforcement and cyclic cumulative deformation of Fujian standard sand were studied. Fiber reinforced soil is a new soil improvement technology. The establishment of stress-strain relationship and related mechanical model of fiber reinforced soil is not only beneficial to predict the strength and deformation characteristics of fiber reinforced soil. It can also provide reference for the engineering design of fiber reinforced soil. At present, the research on mechanical model and calculation theory of fiber reinforced soil is always weak in this field. In this paper, the fiber reinforced soil is considered as the combination of basic phase and fiber phase. The modified Cambridge model and the linear elastic model are used to consider the yield of the fiber reinforced soil when the strain is large, and the reasonable strength model of the reinforced soil is introduced as the failure criterion. Thus a two-phase constitutive model of fiber reinforced soil is established. At the same time, the triaxial consolidation and drainage shear tests of reinforced sand with fiber volume of 1% were carried out, and the two-phase constitutive model was verified. In recent years, offshore wind power industry is developing very rapidly. The foundation of offshore wind turbine is often subjected to cyclic loads such as wind, wave, current and even earthquake. Under the action of long term cyclic reciprocating load, the foundation will often produce cyclic cumulative deformation, which will affect the normal operation of offshore wind turbine. In this paper, a series of unidirectional cyclic triaxial compression and tensile tests of saturated sand have been carried out. The dynamic stress level, initial average stress and initial static stress ratio have been studied. The effect of initial compactness on cyclic cumulative deformation of Fujian standard sand shows that the larger the ratio of dynamic stress, initial mean stress and initial static stress, the smaller the initial compactness, the greater the cyclic cumulative deformation of sand. Then, the data of cyclic triaxial test are analyzed, and the logarithmic linear relationship between axial cyclic cumulative strain and cyclic number is obtained, and all the influencing factors are included in the first axial cyclic cumulative strain. The relationship between the first axial cyclic cumulative strain and the initial average stress and deflection stress level is analyzed. Finally, based on the reasonable calculation model of cyclic cumulative deformation of soft clay, the definition of deflection stress level is modified appropriately, and the theory of sand shear strength related to compactness is introduced. An explicit model of cyclic cumulative deformation of saturated sand is established and verified by cyclic triaxial test.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU411;TU441
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