非饱和黄土结合水特性及水分迁移问题研究
发布时间：2019-04-24 13:47
【摘要】：非饱和黄土遍布黄土高原,其水分状态对其工程性质有显著影响,目前对其水分状态尤其是结合水状态的研究尚欠缺。论文通过等温吸附法和热重分析法确定了黄土中强结合水和弱结合水的含量,试验结果表明黄土中结合水的含量主要与粘土矿物的含量有关,并且随着粘土矿物含量的增加而增加,建立了不同类型结合水含量与粘土矿物含量之间的关系式,并通过试验和理论分析相结合的方法确定了不同类型的结合水的密度和水膜厚度。吸力是影响非饱和土渗流问题的重要变量,不同含水量水平的土体可存在不同吸力类型,其对渗流问题有不同影响,目前针对非饱和土渗流问题尚缺乏对吸力的分类的研究。为此,在分析孔隙水赋存状态及及其吸力作用的基础上,将非饱和土中孔隙水分为结合水、毛细角边水和连通毛细水三种类型,非饱和土中的吸力可分为吸附作用力、吸附毛细作用力和毛细作用力。结合水在自然条件下的迁移可以忽略不计,处于毛细角边水状态的非饱和土以气态水迁移为主,当非饱和土中的毛细水连通时,水分以液态水迁移为主,并给出了非饱和土黄土结合水、毛细角边水和毛细水的界限含水量。进一步在物理化学相关原理的基础上给出了吸附作用力的理论计算公式,吸附作用力可以通过结合水化学势能的减小量来衡量;基于分析非饱和土中吸附毛细作用力的作用效应,给出了吸附毛细作用力的确定方法;基于非饱和土力学原理列出了毛细作用力的确定方法,并对其适用性进行了评述。固-液接触角的不易确定性和孔径分布的随机性致使毛细作用力的理论计算公式难以在实际中应用,因此,往往通过以陶瓷板为代表的高进气材料来测定土体中的吸力。基于对水-气-陶瓷板-非饱和土测试系统的分析,给出了毛细作用力量测时适宜的含水量范围,只有当非饱和土中的毛细水处于联通状态时才可以通过该系统量测非饱和土中的吸力。基于上述分析,选择毛细水连通的非饱和黄土,开展了其在基质势梯度作用下的水分迁移试验。试验结果表明,毛细水连通状态下的非饱和黄土中的水分迁移量大体上随着基质势梯度的增加而增加,并建立了水分迁移量与基质势梯度之间的统计关系式,可为评价基质势梯度对水分迁移的驱动作用所参考。进一步针对黄土高原旱区浅层土体水分场随气候变化问题,开展了非饱和黄土在温度梯度作用下的气态水迁移和液态水迁移试验。试验结果表明,气态水迁移量和液态水迁移量均随着温度梯度的增加而增加,气态水迁移量的增加幅度显著大于液态水迁移量的增加幅度。在气态水迁移中,温度效应随着土样初始含水量的增加而显著增加;在液态水迁移中,温度效应与土样初始含水量的关系不大。在对试验结果分析的基础上,建立了综合考虑温度梯度和初始含水量影响的非饱和黄土稳态时含水量梯度的关系式。最后,在上述研究成果的基础上完善了非饱和土二维非稳态有限元计算方法,并对黄土高原浅层土体水分场在连续干旱条件下的动态变化进行了数值分析。水分场的数值计算结果与实测结果较为一致,表明了用数值计算预测浅层黄土水分场动态变化的可靠性。基于实测和计算结果,分析得到了黄土高原旱区浅层土体水分场在连续干旱条件下的变化规律以及土层含水量在不同干旱时间范围内的减小程度,可以为黄土高原旱区植物防护工程建设所参考。
[Abstract]:Unsaturated loess is all over the loess plateau and its water status has a significant impact on its engineering properties. The results show that the content of the combined water in the loess is mainly related to the content of the clay minerals, and the content of the clay minerals increases with the increase of the content of the clay minerals. The relation between water content and clay mineral content of different types is established, and the density and water film thickness of different types of combined water are determined by the combination of experimental and theoretical analysis. The suction force is an important variable which influences the seepage of unsaturated soil, and the soil body with different water content level can have different suction types. It has different influence on the seepage problem. At present, the study on the classification of suction force is still lacking for the seepage problem of unsaturated soil. For this purpose, on the basis of analyzing the occurrence state of pore water and its suction effect, the pore water in unsaturated soil is three types of combined water, capillary angle edge water and communication capillary water, and the suction force in unsaturated soil can be divided into adsorption force, adsorption capillary force and capillary force. the migration of the combined water under natural conditions is negligible, and the unsaturated soil in the water state of the capillary angle is mainly transferred by the gaseous water, and when the capillary water in the unsaturated soil is in communication, the water is mainly transported by the liquid water, and the unsaturated soil loess is combined with water, The boundary water content of the capillary water and the capillary water. The theoretical calculation formula of the adsorption force is given on the basis of the physical and chemical related principle, and the adsorption force can be measured by combining the reduction of the water chemical potential energy; and based on the action effect of the adsorption capillary force in the unsaturated soil, The determination method of the adsorption capillary force is given, and the determination method of the capillary force is listed on the basis of the principle of unsaturated soil mechanics, and the applicability of the method is reviewed. The uncertainty of the solid-liquid contact angle and the randomness of the pore size distribution make the theoretical calculation formula of the capillary force difficult to apply in practice, and therefore, the suction force in the soil body is often determined by the high intake material represented by the ceramic plate. Based on the analysis of the water-gas-ceramic plate-unsaturated soil test system, the water content range of the water-gas-ceramic plate-unsaturated soil test system is given, and the suction force in the unsaturated soil can be measured by the system only when the capillary water in the unsaturated soil is in the communication state. Based on the above analysis, the unsaturated loess with capillary water communication is selected, and the water migration test under the influence of the matrix potential gradient is carried out. The experimental results show that the amount of water migration in the unsaturated loess in the capillary water communication is generally increased with the increase of the matrix potential gradient, and the statistical relation between the moisture migration amount and the matrix potential gradient is established. It can be used to evaluate the driving effect of the matrix potential gradient on the migration of water. In the light of the problem of climate change, the water migration and liquid water migration test of unsaturated loess under the action of temperature gradient are carried out in the light of the problem of climate change. The experimental results show that both the amount of gas migration and the amount of liquid water migration increase with the increase of the temperature gradient, and the increase of the amount of gas migration is significantly higher than that of liquid water. In the gas migration, the temperature effect is obviously increased with the increase of the initial water content of the soil sample; in the liquid water migration, the temperature effect is not related to the initial water content of the soil sample. On the basis of the analysis of the test results, the relationship of the water content gradient of unsaturated loess with the influence of temperature gradient and initial water content is established. Finally, on the basis of the above research results, the two-dimensional non-steady-state finite element method of unsaturated soil is improved, and the dynamic changes of the water field of the shallow soil in the Loess Plateau under continuous drought conditions are analyzed. The numerical results of the water field are consistent with the measured results, and the reliability of the dynamic change of the water field of the shallow loess is predicted by numerical calculation. Based on the measured and calculated results, the variation law of the moisture field of the shallow soil in the arid area of the Loess Plateau and the degree of reduction of the water content of the soil layer in the range of different drought time are obtained, which can be referred to in the construction of plant protection in the dry area of the Loess Plateau.
【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU444
[Abstract]:Unsaturated loess is all over the loess plateau and its water status has a significant impact on its engineering properties. The results show that the content of the combined water in the loess is mainly related to the content of the clay minerals, and the content of the clay minerals increases with the increase of the content of the clay minerals. The relation between water content and clay mineral content of different types is established, and the density and water film thickness of different types of combined water are determined by the combination of experimental and theoretical analysis. The suction force is an important variable which influences the seepage of unsaturated soil, and the soil body with different water content level can have different suction types. It has different influence on the seepage problem. At present, the study on the classification of suction force is still lacking for the seepage problem of unsaturated soil. For this purpose, on the basis of analyzing the occurrence state of pore water and its suction effect, the pore water in unsaturated soil is three types of combined water, capillary angle edge water and communication capillary water, and the suction force in unsaturated soil can be divided into adsorption force, adsorption capillary force and capillary force. the migration of the combined water under natural conditions is negligible, and the unsaturated soil in the water state of the capillary angle is mainly transferred by the gaseous water, and when the capillary water in the unsaturated soil is in communication, the water is mainly transported by the liquid water, and the unsaturated soil loess is combined with water, The boundary water content of the capillary water and the capillary water. The theoretical calculation formula of the adsorption force is given on the basis of the physical and chemical related principle, and the adsorption force can be measured by combining the reduction of the water chemical potential energy; and based on the action effect of the adsorption capillary force in the unsaturated soil, The determination method of the adsorption capillary force is given, and the determination method of the capillary force is listed on the basis of the principle of unsaturated soil mechanics, and the applicability of the method is reviewed. The uncertainty of the solid-liquid contact angle and the randomness of the pore size distribution make the theoretical calculation formula of the capillary force difficult to apply in practice, and therefore, the suction force in the soil body is often determined by the high intake material represented by the ceramic plate. Based on the analysis of the water-gas-ceramic plate-unsaturated soil test system, the water content range of the water-gas-ceramic plate-unsaturated soil test system is given, and the suction force in the unsaturated soil can be measured by the system only when the capillary water in the unsaturated soil is in the communication state. Based on the above analysis, the unsaturated loess with capillary water communication is selected, and the water migration test under the influence of the matrix potential gradient is carried out. The experimental results show that the amount of water migration in the unsaturated loess in the capillary water communication is generally increased with the increase of the matrix potential gradient, and the statistical relation between the moisture migration amount and the matrix potential gradient is established. It can be used to evaluate the driving effect of the matrix potential gradient on the migration of water. In the light of the problem of climate change, the water migration and liquid water migration test of unsaturated loess under the action of temperature gradient are carried out in the light of the problem of climate change. The experimental results show that both the amount of gas migration and the amount of liquid water migration increase with the increase of the temperature gradient, and the increase of the amount of gas migration is significantly higher than that of liquid water. In the gas migration, the temperature effect is obviously increased with the increase of the initial water content of the soil sample; in the liquid water migration, the temperature effect is not related to the initial water content of the soil sample. On the basis of the analysis of the test results, the relationship of the water content gradient of unsaturated loess with the influence of temperature gradient and initial water content is established. Finally, on the basis of the above research results, the two-dimensional non-steady-state finite element method of unsaturated soil is improved, and the dynamic changes of the water field of the shallow soil in the Loess Plateau under continuous drought conditions are analyzed. The numerical results of the water field are consistent with the measured results, and the reliability of the dynamic change of the water field of the shallow loess is predicted by numerical calculation. Based on the measured and calculated results, the variation law of the moisture field of the shallow soil in the arid area of the Loess Plateau and the degree of reduction of the water content of the soil layer in the range of different drought time are obtained, which can be referred to in the construction of plant protection in the dry area of the Loess Plateau.
【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU444
【参考文献】
相关期刊论文 前10条
1 Man CHENG;Shao Shan AN;;Responses of soil nitrogen, phosphorous and organic matter to vegetation succession on the Loess Plateau of China[J];Journal of Arid Land;2015年02期
2 钱峰;程冬兵;刘静君;;土壤蒸发强度随土壤溶液盐分的变化研究[J];长江科学院院报;2015年03期
3 杨松;龚爱民;吴s，
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