农安盐渍土冻胀及反复冻融强度衰减特性研究

发布时间：2018-09-01 17:33

【摘要】：盐渍土对工程建设的危害是多方面的，由此造成的经济损失也十分巨大。吉林省农安县属于典型季冻区，分布着大量盐碱化较重的土壤，该地区的各类土木工程经常会受到碳酸盐渍土的冻胀和反复冻融的影响。路基路面的冻胀翻浆、堤坝坡脚的冻胀开裂和冻融作用下盐渍土地基的承载力不足等病害，已经成为制约盐渍土工程成败的关键。为给碳酸盐渍土地区盐渍土工程的冻胀和反复冻融强度的破坏寻找理论依据和机制，本文结合国家自然科学基金项目松嫩平原分散土成因机制及水热盐耦合离子迁移模型研究（No.41372267）、寒旱区土体盐渍化HTSM多场耦合地质环境系统灾变演化机理与工程效应研究（No.41430642）和高校博士点基金项目干湿冻融循环对吉林西部分散土的影响及机理研究（No.20120061110054），以农安县的碳酸盐渍土土样为研究对象，分别对其进行了冻胀和反复冻融作用下的超声波波速和单轴抗压强度研究。首先对土样的基本物理化学性质进行试验分析，确定农安盐渍土为易溶盐含量较高、弱碱性、非有机质、级配良好、中液限、钠离子含量很高的碳酸粉质亚粘土。再结合工程实际情况制备不同的含盐量、击实度和含水率土样，进行盐渍土冻胀性试验，试验结果表明冻胀性与含水率成正比，最低含水率在16%以上；低含盐量土冻胀与击实度成正比，，高含盐量土冻胀与击实度成反比；含盐量小于1.5%时冻胀与含盐量成正比，反之成反比。然后考虑含盐量、击实度、含水率和冻融次数4个因素的影响对土样进行反复冻融情况下的超声波波速和单轴抗压强度研究。超声波测试分析结果表明，各试验工况土样的波速随着冻融次数呈下降趋势，不含盐土波速与含水率成明显的反比关系。而盐渍土波速在冻融550次时，与含水率成正比关系，波速与击实度总体呈正比关系；反复冻融作用下单轴抗压强度研究表明冻融强度随冻融循环次数而衰减，冻融强度与击实度成正比，与含水率、含盐量成反比关系。通过反复冻融强度和波速的关联性分析，从机制学角度讨论了影响二者关联性的因素水平及规律，以期将这种无损检测强度的手段应用到今后强度测试中。最后，由灰关联度和粗糙集确定盐渍土反复冻融强度衰减的主要影响因素及权重大小顺序为冻融次数含水率击实度含盐量。以击实度、含水率、含盐量、冻融次数建立了冻融强度衰减BP神经网络预报模型，该模型具有很好的收敛性，但测试误差起伏略大，在一定条件下该模型能较好的预测和描述碳酸盐渍土的反复冻融强度，可以为工程设计提供一些参考。
[Abstract]:Salinized soil is harmful to engineering construction in many aspects, and the economic loss caused by it is also very great. Nong'an County of Jilin Province is a typical seasonal frozen area, where a large number of salinized soils are distributed. Various civil engineering projects in this area are often affected by the frost heaving and repeated freezing and thawing of carbonate soil. The diseases such as frost heaving of roadbed and pavement, frost heaving cracking of embankment slope foot and insufficient bearing capacity of salinized soil foundation under freezing and thawing have become the key to restrict the success or failure of salinized soil engineering. In order to provide theoretical basis and mechanism for frost heaving and repeated freezing and thawing strength damage of saline soil in carbonate soil area, In this paper, the genetic mechanism of dispersed soil in Songnen Plain and the model of water-thermal-salt-coupled ion migration (No.41372267), the catastrophic evolution mechanism and engineering effect of HTSM multi-field coupled geological environment system of soil salinization in cold and arid region are studied in combination with the project of National Natural Science Foundation of China. The effect and mechanism of dry-wet freezing and thawing cycle on dispersed soil in western Jilin Province (No.20120061110054) were studied by No.41430642 and Ph.D. Foundation Project. The carbonate soil samples in Nong'an County were taken as the research object. The ultrasonic wave velocity and uniaxial compressive strength were studied under frost heaving and repeated freezing thawing respectively. Firstly, the basic physical and chemical properties of soil samples were analyzed, and it was determined that Nong'an saline soil was a carbonated silty clay with high soluble salt content, weak alkalinity, non-organic matter, good grading, medium liquid limit and high sodium ion content. The frost heaving test of salinized soil is carried out. The results show that the frost heave property is proportional to the water content, and the minimum moisture content is above 16%. The frost heave of low salinity soil is directly proportional to the compaction degree, the frost heave of high salinity soil is inversely proportional to the compaction degree, and the frost heave is directly proportional to the salt content when the salt content is less than 1.5, and vice versa. Then the ultrasonic wave velocity and uniaxial compressive strength of soil samples under repeated freezing and thawing were studied by considering the effects of salt content compaction degree moisture content and freeze-thaw times. The results of ultrasonic test show that the wave velocity of soil samples decreases with the freezing and thawing times, and the wave velocity is inversely proportional to the moisture content of the soil without salt. The wave velocity of salinized soil is proportional to water content at 550 times of freezing and thawing, and the wave velocity is proportional to the compaction degree as a whole, and the compressive strength of the order shaft sent out by repeated freezing and thawing process shows that the freezing and thawing strength attenuates with the number of freeze-thaw cycles. The freeze-thaw strength is proportional to compactness, inversely proportional to water content and salt content. Based on the correlation analysis of repeated freezing and thawing strength and wave velocity, the level and law of factors affecting the correlation between them are discussed from the point of view of mechanism, in order to apply this nondestructive testing method to the strength test in the future. Finally, the main influencing factors and weight of repeated freezing and thawing strength attenuation of saline soil are determined by grey correlation degree and rough set. The order of weight is water content of freezing and thawing times, compaction degree of water content. The BP neural network prediction model of freezing and thawing strength attenuation is established by using compaction, water content, salt content and freeze-thaw times. The model has good convergence, but the measurement error fluctuates slightly. Under certain conditions, the model can predict and describe the repeated freezing and thawing strength of carbonate soil, and can provide some references for engineering design.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU448

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