基于滤纸法的黄土土—水特征曲线测试

发布时间：2018-11-11 20:01

【摘要】：非饱和土与饱和土的根本差异在于非饱和土中的孔隙水压力为负值。孔隙气压与负孔隙水压力的差值定义为基质吸力,用来体现非饱和土的应力特征。将基质吸力与土含水率的关系曲线称为土-水特征曲线(Soil-Water Characteristic Curve),简称SWCC。SWCC是非饱和土的一个重要本构关系,可以用来分析和预测土的变形、强度和渗透性,因此SWCC是非饱和土研究的基础。基质吸力测试方法较多,其中滤纸法最为快捷、简便且量程大。本文取陕西泾阳L1和L5黄土样,在ASTM D5298-10的基础上,研究滤纸法测试基质吸力的操作过程,重点对土样的制备和试验条件、滤纸的称量、平衡时间等关键步骤进行分析和改进,将测试结果与其他方法进行对比,主要结论有:1)实验密封条件采用锡纸包裹并蜡封的方法代替ASTM D5298-10推荐的密封罐,解决了密封罐易造成密封不严及取放土样不便的问题,密封结果更为理想;2)由铝盒或者保鲜袋为滤纸的容器称量滤纸改为直接将滤纸放在天平托盘上称量,提高了称量滤纸的精度;3)对于同一种土,多组环刀联合测试与只采用一组环刀测试相比,更易于操作,且减小了操作过程中的误差;4)土样与滤纸的水势平衡时间与土样的干密度关系小,与土样的含水率关系较大,含水率越大平衡时间越短,反之,平衡时间越长,对于泾阳L1和L5黄土,土样含水率小于5%时,建议平衡时间13天以上;土样含水率介于5%~20%之间,建议平衡时间为10天以上;含水率大于20%时,建议平衡时间为5天以上;5)分别采用Gardner模型、Van Genuchten模型和FredlundXing模型对滤纸法所获基质吸力及土样实际含水率进行SWCC拟合,FredlundXing模型拟合度最高;6)通过将已有采用张力计、压力板仪、压力膜仪、渗析法及滤纸法等测得的黄土SWCC与本文滤纸法测试结果对比,证明本文推荐的方法和所测试的结果可靠性高且在全基质吸力范围内均较为适用。
[Abstract]:The fundamental difference between unsaturated soil and saturated soil is that the pore water pressure in unsaturated soil is negative. The difference between pore pressure and negative pore water pressure is defined as matrix suction, which is used to reflect the stress characteristics of unsaturated soil. The relation curve between matrix suction and soil moisture content is called the soil-water characteristic curve (Soil-Water Characteristic Curve), which is an important constitutive relation of unsaturated soil. It can be used to analyze and predict the deformation, strength and permeability of soil. Therefore, SWCC is the basis of unsaturated soil research. There are many methods of matrix suction measurement, among which filter paper method is the most rapid, simple and has a large measuring range. On the basis of ASTM D5298-10, the operating process of filter paper method for measuring the suction of the matrix was studied, and the preparation and test conditions of the soil samples, the weighing of filter paper, were studied in this paper, taking the loess samples of Jingyang, Shaanxi Province, as well as the L _ 5 loess samples, and based on ASTM D5298-10. The key steps, such as balance time, are analyzed and improved, and the test results are compared with other methods. The main conclusions are as follows: 1) the experimental sealing conditions are replaced by the seal tank recommended by ASTM D5298-10. The problem that the sealing tank is easy to be sealed and the soil sample is not easy to be taken is solved, and the sealing result is more ideal. 2) the weighing filter paper is changed from the container weighing filter paper of aluminum box or fresh-keeping bag to the weighing paper directly on the balance tray, which improves the accuracy of weighing filter paper; 3) for the same soil, it is easier to operate and the error in the operation process is reduced compared with that of using only one group of ring knives. 4) the water potential equilibrium time of soil sample and filter paper has little relationship with dry density of soil sample, and has a greater relation with soil sample moisture content. The larger the water content is, the shorter the equilibrium time is, otherwise, the longer the equilibrium time is, the longer the balance time is, and the longer the balance time is, the longer the balance time is for Jingyang L1 and L5 loess. When the moisture content of soil sample is less than 5, it is suggested that the balance time be more than 13 days. The water content of soil sample is between 5% and 20%, and the suggested equilibrium time is more than 10 days, and when the moisture content is more than 20, the suggested equilibrium time is more than 5 days. 5) Gardner model, Van Genuchten model and FredlundXing model were used to fit the matrix suction and soil sample moisture content obtained by filter paper method respectively. FredlundXing model had the highest fitting degree. 6) the SWCC of loess measured by tension meter, pressure plate instrument, pressure film meter, dialysis method and filter paper method are compared with the results of filter paper method in this paper. It is proved that the proposed method and the measured results are reliable and applicable in the whole matrix suction range.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU444

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