导　　师： 朱斌

学科专业： 081401

授予学位： 硕士

作　　者： ;

机构地区： 浙江大学

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。 Geotechnical constitutive modelling, which studys stress-strain relations laws of soil, is an important theoretical basis for geotechnical engineering disciplines, and provide a theoretical basis and guidance for the analysis and design of geotechnical engineering. Sandy soil has a wide distribution in our country. Scholars at home and abroad have carried out a number of studies on sand's basic mechanical properties and established a wide variety of constitutive models. In recent decades, many new hydraulic and power projects, high-rise buildings and traffic engineering are springing up, bringing a lot of new geotechnical problems, such as sand fiber reinforcement and cyclic accumulated deformation of sands. Fujian sand is a representative kind of sand for experiment in our country. In this paper, a series of static and dynamic triaxial tests were carried out to study the fiber reinforcement and cyclic accumulative deformation properties of Fujian sand, and constitutive models were developed based on the test datas. Fiber reinforcement is a new type of fiber reinforced soil improvement technique. Studying the stress-strain relationship laws of fiber reinforced soil and establishing the associated mechanical model are not only beneficial for forecasting the strength and deformation characteristics of fiber reinforced soil, but also to provide a reference for the engineering design of fiber reinforced soil. The current works about the theories of fiber reinforced soil mechanical models and calculations are still not mature. In this article, a constitutive model of fiber reinforced soil is developed considering the fiber reinforced soil as a kind of composite material comprising of basic phase and fiber phase, which is based on modified Cambridge model and linear elastic model respectively. A reasonable strength model is introduced as the failure criterion for the fiber reinforced soil and fiber reinforcement weakening at large strain is also taken into account. At the same time, launched a fiber volume fraction of1/%of the reinforced sand consolidated drained triaxial shear tests, the two-phase constitutive model was validated. Then the two-phase constitutive model is validated by a series of triaxial consolidated compression tests of fiber reinforced sand with1/%volume fraction of fiber and provide good agreement with experimental data. In recent years, the development of offshore wind power industry is soaring. The foundations of offshore wind turbines are often subjucted to cyclic loads such as wind, waves, currents and even earthquakes. Under long-term cyclic loads, it is tend to produce cyclic accumulative deformation of the soils around foundation, which affecting the normal operation of offshore wind turbines. In this paper, a series of cyclic triaxial compression and tension tests of saturated sands under drainage condition have been carried out, to study the influences of dynamic stress level, initial mean stress, initial static stress ratio and initial density on the accumulative deformation characteristics of Fujian sand, fingding that when dynamic stress, initial mean stress and initial static stress ratio increases and initial density decreaces, the cyclc accumulative deformation is smaller. A double logarithmic linear relationship between the axial accumulative strain and cycles was obtained from cyclic triaxial tests and all the factors were included in the first cyclic accumulative axial strain. After that, the relationship between the first cyclic accumulative axial strain and the initial mean stress and deviatoric stress levels were analyzed. Finally, a explicit model for the accumulation of strain in saturated sand is developed based on a reasonable explicit model for the accumulation of strain in saturated soft clay in which the definition of deviatoric stress level was properly corrected and a strength theory of sand associated with relative density was introduced in it. The explicit model was verified by the data of cyclic triaxial tests.

关 键 词： 本构模型 福建标准砂 纤维加筋 两相 三轴试验 循环累积变形 偏应力水平 显式计算模型

分 类 号： [TU411 TU441]

领　　域： [建筑科学] [建筑科学] [建筑科学] [建筑科学]