人工冻结海相软土冻胀特性研究

发布时间：2019-01-27 10:48

【摘要】：我国沿海地区广泛分布着深厚的海相沉积软土层,人工地层冻结技术作为一种地层加固技术,可以有效地解决海相软土强度低、蠕变性、触变性等工程性质差的难题。但是,在海相软土层中应用人工地层冻结技术,一方面其热物理与力学参数研究较少,缺少相应的基础数据,另一方面,人工冻结海相软土冻胀特性的研究尚处于空白状态。为了满足海相软土地层应用人工地层冻结技术的需要,本文采用室内试验、理论推导与数值模拟相结合的研究方法,对人工冻结条件下海相软土的冻胀特性开展了一系列研究。首先,通过室内试验对人工冻结条件下海相软土的热物理与力学参数进行研究。海相软土由于受到海水的入侵,导致其内部含有一定量的易溶盐。在对宁波地区两种典型的海相软土层进行室内含盐量测定的基础上,研究了海相软土的起始冻结温度、导热系数、冻土比热、冻土弹性模量及冻土单轴抗压强度等热物理与力学参数,得出了不同影响因素对海相软土热物理与力学参数的影响规律。其次,通过室内冻胀试验对人工冻结条件下海相软土的冻胀特性开展研究。在自行设计并加工的一套简易的室内冻胀试验装置上,开展冻胀率单因素试验与冻胀率正交试验。室内冻胀试验是自下而上一维冻结条件下进行的,测出土体试样的冻胀量,冻胀率通过计算得到,并得出了含盐量、含水率、冷端温度、外部荷载四个因素对海相软土冻胀率的影响规律以及四个因素之间的主次关系。同时,通过对冻胀试验过程中温度监测及冻结后土体试样不同部位含水率的测量,得出试验过程中温度场的发展规律与水分重分布的规律。再者,考虑了海相软土降温冻结过程中二次相变的现象,对已有的水分场、盐分场、温度场以及应力场方程进行了修正,建立了人工冻结海相软土水-盐-热-力四场耦合的冻胀预报模型。最后,在对已建立的冻胀预报模型进行合理简化之后,通过有限元数值模拟软件COMSOL二次开发中的PDE模块,对已建立的冻胀预报模型进行了求解计算,从而实现了对已建立的冻胀预报模型的验证。将数值模拟的计算结果与室内冻胀试验的测量结果进行了对比,二者相互印证了本文对人工冻结条件下海相软土冻胀特性规律研究的正确性。
[Abstract]:Deep marine sedimentary soft soil is widely distributed in coastal areas of China. As a kind of stratum strengthening technology, artificial stratum freezing technology can effectively solve the problems of low strength, creep, thixotropy and other engineering properties of marine soft soil. However, in the application of artificial stratum freezing technology in marine soft soil, on the one hand, the study of thermal physical and mechanical parameters is less, and the corresponding basic data is lacking; on the other hand, the research on the frost heave characteristics of artificial frozen marine soft soil is still in blank state. In order to meet the need of applying artificial formation freezing technology in marine soft soil, this paper has carried out a series of research on the frost heave characteristics of marine soft soil under artificial freezing condition by means of laboratory test, theoretical derivation and numerical simulation. Firstly, the thermal physical and mechanical parameters of marine soft soil under artificial freezing condition were studied. Due to the invasion of sea water, marine soft soil contains a certain amount of soluble salt. Based on the indoor measurement of salt content in two typical marine soft soil layers in Ningbo area, the initial freezing temperature, thermal conductivity and specific heat of frozen soil are studied. The thermal physical and mechanical parameters such as elastic modulus of frozen soil and uniaxial compressive strength of frozen soil are obtained. The influence of different factors on the thermal physical and mechanical parameters of marine soft soil is obtained. Secondly, the frost heaving characteristics of marine soft soil under artificial freezing condition are studied by indoor frost heaving test. The single factor test and orthogonal test of frost heave rate were carried out on a set of simple indoor frost heave test device designed and processed by ourselves. The indoor frost heave test was carried out under the condition of one-dimensional freezing from bottom to top. The frost heave quantity of soil sample was measured, and the frost heave rate was calculated, and the salt content, moisture content and cold end temperature were obtained. The influence of four factors of external load on the frost heaving rate of marine soft soil and the primary and secondary relationship between the four factors. At the same time, through the temperature monitoring during the frost heave test and the measurement of moisture content in different parts of the frozen soil sample, the development law of the temperature field and the law of water redistribution during the test process are obtained. Furthermore, considering the phenomenon of secondary phase transition in the process of cooling and freezing of marine soft soil, the existing equations of water field, salt field, temperature field and stress field are modified. The frost heaving prediction model of artificial frozen marine soft soil is established in this paper, which is coupled with water, salt, heat and force. Finally, after reasonable simplification of the established frost heave prediction model, the established frost heave prediction model is solved by the PDE module in the secondary development of the finite element numerical simulation software COMSOL. Thus the verification of the established frost heave prediction model is realized. The calculated results of numerical simulation are compared with the measured results of indoor frost heave test. Both of them confirm the correctness of the research on the frost heave characteristics of marine soft soil under artificial freezing condition.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU447

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