含新型元件的蠕变模型二次开发研究

发布时间：2018-12-20 08:17

【摘要】：土体流变是个很宽泛的概念,它包含蠕变、应力松弛和长期强度等几个方面,其中土体受荷产生一个完整的蠕变过程包含初始蠕变、稳定蠕变和加速蠕变三个阶段,其应变随时间的变化关系应当呈现出一条近似的“S”形曲线。另外,土体是由散粒体颗粒组成不同于一般的固体材料,其流变过程具有广泛的非线性变形特性。黏土由于它独有的自身结构和属性使得它区别于一般的土体,工程建设中常见的黏土地层或夹层给工程施工带来一定的难度,也给其上建筑物的稳定性带来一些隐患,所以对黏土的物理力学性质和流变特性研究显得尤为重要。本文基于对湛江黏土进行三轴排水蠕变试验所得蠕变数据,采用经典Burger蠕变模型发现不能精确地描述该黏土蠕变前两阶段。提出采用分数阶导数元件(又称阿贝尔元件)替换Burger蠕变模型中相关粘壶,形成新的含一个及两个分数阶导数元件蠕变模型,分别命名为Kburger和Sburger。导出它们一维及三维状态下本构关系式并与经典Burger模型三维本构关系进行对比,寻找三类模型之间的异同点;然后以内置Burger模型程序文件为蓝本,采用C++语言进行更改实现两类分数阶导数模型的定义。在Visual studio 2005以上版本编程平台生成动态链接库(.dll),进而同FLAC3D进行接口、调用,完成二次开发工作并进行验证,结合对湛江黏土在50Kpa恒定围压不同等级偏应力状态下蠕变试验数据拟合出各模型相关计算参数。通过建立模拟三轴蠕变数值算例对比各模型在不同偏应力下描述湛江黏土蠕变过程的优劣性,将模型试样由柱体改为立方体,讨论不同形状试样对三轴蠕变数值计算的影响;其次,鉴于实际土体长期受荷发生变形其强度参数随时间会产生变化且土体具有塑性变形特性,引入变强度参数塑性元件,将该元件与经典Burger模型串联形成变强度参数模型,分析强度参数按不同函数形式变化对土体加速蠕变阶段的影响;最后,将该塑性元件与前述Sburger模型进行串联得到新的分数阶变强度参数模型,结合西南某县在建水工大坝工程,分别选用Cvisc模型、变强度参数模型和分数阶变强度参数模型预测其竣工后沉降趋势并进行对比,分析各模型数值计算结果之间的差异,给出该坝施工时的一些建议。
[Abstract]:Soil rheology is a very broad concept, which includes creep, stress relaxation and long-term strength, among which a complete creep process caused by soil load consists of three stages: initial creep, stable creep and accelerated creep. The variation of strain with time should show an approximate "S" curve. In addition, the soil is a solid material which is composed of granular particles, and its rheological process has a wide range of nonlinear deformation characteristics. Clay is different from ordinary soil because of its unique structure and property. The common clay stratum or interlayer in engineering construction brings some difficulty to engineering construction, and also brings some hidden trouble to the stability of the building on it. Therefore, it is very important to study the physical and mechanical properties and rheological properties of clay. Based on the creep data obtained from the triaxial drainage creep test of Zhanjiang clay, the classical Burger creep model is used to find that the first two stages of the creep of the clay can not be accurately described. A new creep model containing one and two fractional derivative elements, named Kburger and Sburger., was proposed to replace the associated kettle in the Burger creep model by using fractional derivative element (also called Abelian element). The constitutive equations in one dimension and three dimensional states are derived and compared with the three dimensional constitutive relations of the classical Burger model to find the similarities and differences between the three models. Then, based on the built-in Burger model program file, the definition of two kinds of fractional derivative model is realized by using C language. The dynamic link library (. Dll),) is generated in the programming platform above Visual studio 2005 and then interfaced with FLAC3D, which is called, and the secondary development is completed and verified. According to the creep test data of Zhanjiang clay under the condition of 50Kpa constant confining pressure and different grade deviant stress, the relevant calculation parameters of each model are obtained. By setting up numerical examples of simulating triaxial creep and comparing the advantages and disadvantages of each model to describe the creep process of Zhanjiang clay under different deflection stress, the model specimen is changed from cylinder to cube, and the influence of different shape specimen on triaxial creep numerical calculation is discussed. Secondly, in view of the fact that the strength parameter will change with time and the soil has plastic deformation characteristic, the variable strength parameter plastic element is introduced, and the variable strength parameter model is formed by using the variable strength parameter plastic element in series with the classical Burger model. The influence of strength parameters on the accelerated creep stage of soil is analyzed according to different function forms. Finally, the plastic element is connected with the Sburger model to get a new fractional variable strength parameter model, and the Cvisc model is selected in combination with the hydraulic dam under construction in a county in southwest China. The variable-strength parameter model and fractional variable-strength parameter model are used to predict the settlement trend after completion of the dam. The difference between the numerical calculation results of each model is analyzed and some suggestions for the dam construction are given.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU442

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