饱和膨胀土冻胀特性及冻胀模型

发布时间：2018-03-08 09:14

  本文选题：饱和膨胀土　切入点：冻胀试验　出处：《哈尔滨工业大学》2016年硕士论文　论文类型：学位论文

【摘要】：我国是一个冻土大国,在世界四大冻土国中位居第三,冻土主要分布于东北、内蒙大部地区与新疆、青海、西藏部分地区。随着我国多年冻土区与季节冻土区普通铁路、高速铁路、快速客运专线、高速公路等建设日益加快,冻害及其防控引起广泛关注。目前,季节冻土区发现大范围膨胀土场地,但是针对寒区膨胀土冻胀特性的研究报道尚且不多。冻土的冻胀变形发展主要受气候条件和地下水条件影响,较难预估其变形大小,有必要研究温度、补水条件等冻胀敏感性因素对变形的影响,为减小冻胀对土工构筑物的危害提供理论依据。本文开展了延吉膨胀土基本物理性质试验、自由膨胀率试验、土水特征曲线试验和冻胀特性试验等试验,重点研究了膨胀土冻胀特性及各因素的影响,基于水-热耦合理论研究了冻胀变形的计算方法。这项工作将有助于分析冻土中的传热、传质规律,预测冻土在不同边值条件下的变形,为冻胀量预测与防冻害提供一定参考。主要研究工作及重要成果如下:首先,通过物理性质试验,获得膨胀土基本物性指标;利用自主研制的冻融循环试验仪FTT1,对饱和与非饱和土分别开展了不同温度梯度、初始含水率和压实度下的冻胀特性试验,得到温度条件是影响开放系统下温度场、水分场以及变形的主要因素之一。试验稳定后,温度沿试样高度近似呈线性分布,冻胀变形主要由分凝冰引起,主要形成于冻结缘冷端。其次,基于质量守恒、能量守恒等基本定律,在微元体层面建立冻土的水-热耦合控制方程组,包括能量守恒方程、质量守恒方程和联系方程,通过有限元分析软件建立饱和土的水-热耦合数值模型,考虑水分迁移和热传导之间的耦合作用,将模拟结果与试验结果对比,验证了模型的正确性。最后,基于分凝势理论,分析温度场各参数对水分迁移速率的影响,讨论冻结缘吸力与温度条件的关系,引入冻结缘吸力描述开放系统下的补水速率,分析了冻深、冻结速率和冷端温度对水分迁移速率的影响,将冻胀变形区分为原位冻胀和迁移冻胀两部分,迁移冻胀占冻胀变形的主要部分,计算结果与试验结果吻合较好。
[Abstract]:China is a great country of frozen soil, ranking third among the four major countries in the world. Frozen soil is mainly distributed in the northeast, most of Inner Mongolia and parts of Xinjiang, Qinghai and Tibet. Along with the permafrost regions in China and the ordinary railways in the seasonal frozen regions, The construction of high-speed railways, high-speed passenger dedicated lines and expressways has been speeding up day by day. Freezing damage and its prevention and control have aroused widespread concern. At present, a large area of expansive soil sites have been discovered in seasonal frozen soil areas. However, there are few reports on frost heave characteristics of expansive soils in cold regions. The development of frost heave deformation of frozen soil is mainly affected by climatic conditions and groundwater conditions, so it is difficult to predict its deformation, so it is necessary to study the temperature. The effect of frost heaving sensitive factors such as rehydration condition on deformation provides a theoretical basis for reducing the damage of frost heave to geotechnical structures. In this paper, the basic physical properties of Yanchi expansive soil and the test of free expansion rate are carried out. The soil water characteristic curve test and frost heave characteristic test, etc., have studied the frost heave characteristic of expansive soil and the influence of various factors. Based on the coupling theory of water and heat, the calculation method of frost heave deformation is studied. This work will be helpful to analyze the law of heat and mass transfer in frozen soil and to predict the deformation of frozen soil under different boundary value conditions. The main research work and important results are as follows: firstly, through physical property test, the basic physical properties of expansive soil are obtained; Using the freeze-thaw cycle tester FTT1 developed by ourselves, the frost heave properties of saturated and unsaturated soils under different temperature gradients, initial moisture content and compactness were tested, respectively. The results show that the temperature conditions affect the temperature field in the open system. One of the main factors of water field and deformation is that the temperature is approximately linearly distributed along the height of the specimen after the experiment is stable, and the frost heave deformation is mainly caused by the freezing ice, which is mainly formed at the cold end of the freezing edge. Secondly, based on the conservation of mass, The basic laws of conservation of energy, such as the conservation of energy, the mass conservation and the relation equation, are established at the level of microelement, and the coupled governing equations of water and heat in frozen soil are established, which include energy conservation equation, mass conservation equation and relation equation. The numerical model of water-heat coupling of saturated soil is established by finite element analysis software. Considering the coupling effect between water migration and heat conduction, the correctness of the model is verified by comparing the simulation results with the experimental results. The influence of temperature field parameters on water migration rate is analyzed, and the relationship between freezing edge suction and temperature condition is discussed. The freezing edge suction is introduced to describe the rehydration rate under the open system, and the freezing depth is analyzed. The effects of freezing rate and cold end temperature on water transfer rate are divided into two parts: in situ frost heave and migration frost heave. The calculated results are in good agreement with the experimental results.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU443
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本文编号：1583281