广西宁明膨胀土的膨胀力试验研究

发布时间：2018-02-20 22:30

本文关键词： 膨胀土恒体积法膨胀力土-水特征曲线相对湿度　出处：《桂林理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：膨胀土遇水膨胀软化、失水收缩干裂,工程性质复杂,常常引发膨胀土所在地区的岩土工程灾害。膨胀土无论是在饱和环境下还是在非饱和环境下,都会发生不同程度的膨胀,表现出不同的膨胀力,给膨胀土所在地区造成工程灾害。尽管目前人们对饱和土的膨胀特性有了较为深入的了解,但是在非饱和环境下有关膨胀土的力学特性的研究仍较为缺乏,尤其是膨胀力的测试及其机理解释方面仍然存在诸多争议。本文针对广西宁明膨胀土在纯水饱和环境与控制湿度的非饱和环境下,分别测量各自的极限膨胀力与自然膨胀力,并分析其膨胀机理。本文的研究内容包括饱和环境下膨胀土极限膨胀力的测试与非饱和环境下膨胀土自然膨胀力的测试,主要成果如下:(1)目前测量土体膨胀力的主要方法有膨胀反压法、加压膨胀法、平衡加压法和恒体积法四种。基于测量膨胀力的恒体积法,利用TST-55型渗透仪、高精度压力传感器和数采系统改进了测量土体膨胀力的装置,并测定了宁明膨胀土的极限膨胀力。试验结果表明,土样初始含水量和干密度对土体的极限膨胀力都存在显著的影响,并建立了极限膨胀力与干密度之间的定量关系式;较低初始含水量时,不同干密度的土样在膨胀力达到峰值之后,均有不同幅度的降低,且随着干密度的增大而降低的越多,并且发现极限膨胀力降低值与干密度之间在双对数坐标轴上存在线性关系;而在较高初始含水量时,不同干密度的土样在膨胀力达到峰值之后,会保持平稳趋势。极限膨胀力的对数值与初始含水量之间具有很好的线性关系,土样吸水量的对数值与初始含水量以及干密度均有着很好的线性关系。(2)为了研究膨胀土在非饱和环境下的膨胀力,结合测量膨胀力的恒体积法与控制吸力的蒸汽平衡法(控制相对湿度),本试验设计了一种能够测量膨胀土在非饱和环境下膨胀力的仪器。本文试验结果表明,膨胀土的自然膨胀力随着相对湿度的增大而增大;通过轴平移法与蒸汽平衡法联合测定全吸力范围内宁明膨胀土的土水特征关系曲线,发现宁明膨胀土的吸湿曲线与脱湿曲线两者不重合,存在滞回现象,构成一个滞回圈。自然膨胀力在到达峰值后会稍微降低,最终达到稳定值,即残余膨胀力;自然膨胀力与残余膨胀力的平衡时间均与相对湿度相关;膨胀力与吸力之间的关系可以采用Fredlund-Xing模型类似的公式进行很好地描述,并获得某一初始状态膨胀土在饱和度任意改变条件下的的膨胀力公式。
[Abstract]:The expansive soil often causes geotechnical engineering disasters in the region where the expansive soil is located due to water swelling and softening, shrinkage and dry cracking of water loss, and complex engineering properties. The expansive soil will expand in varying degrees in both saturated and unsaturated environments. Showing different expansive forces, causing engineering disasters to the region where the expansive soils are located, although people now have a deeper understanding of the expansion characteristics of saturated soils. However, the study on the mechanical properties of expansive soil in unsaturated environment is still lacking. In particular, there are still many controversies in the measurement of expansive force and the explanation of its mechanism. In this paper, the limit expansion force and natural expansion force of Ningming expansive soil in pure water saturated environment and unsaturated environment with controlled humidity are measured respectively. The research contents of this paper include the measurement of the limit expansive force of expansive soil in saturated environment and the test of natural expansive force of expansive soil in unsaturated environment. The main results are as follows: (1) at present, the main methods for measuring the swelling force of soil are four kinds: the method of back pressure, the method of expansion under pressure, the method of balance pressure and the method of constant volume. Based on the constant volume method of measuring expansion force, the TST-55 type osmometer is used. The high precision pressure sensor and the data mining system have improved the device of measuring the soil swelling force and measured the limit expansion force of Ningming expansive soil. The test results show that, The initial water content and dry density of soil samples have a significant effect on the limit expansion force of soil, and the quantitative relationship between the limit expansion force and dry density is established, and when the initial water content is low, the quantitative relationship between the limit expansion force and the dry density is established. Soil samples with different dry densities decreased in different amplitude after the peak expansion force, and with the increase of dry density, the more decreased, It is also found that there is a linear relationship between the decreasing value of limit expansion force and the dry density on the double logarithmic coordinate axis, and when the initial water content is higher, the soil samples with different dry densities reach the peak value after the expansion force reaches the peak. The logarithmic value of the limit expansion force has a good linear relationship with the initial water content, The logarithmic values of water absorption of soil samples have a good linear relationship with the initial water content and dry density. Combining the constant volume method of measuring expansion force with the steam equilibrium method of controlling suction (controlling relative humidity), an instrument is designed to measure the expansion force of expansive soil in unsaturated environment. The natural expansive force of expansive soil increases with the increase of relative humidity, and the soil-water characteristic curves of Ningming expansive soil in the range of full suction are determined by axial translation method and steam equilibrium method. It is found that the hygroscopic curve and dehumidification curve of Ningming expansive soil do not coincide with each other, and there exists hysteresis, which forms a hysteresis loop. The natural expansion force will decrease slightly after reaching the peak value, and finally reach the stable value, that is, residual expansion force. The equilibrium time of natural expansion force and residual expansion force is related to relative humidity, the relationship between expansion force and suction force can be well described by the similar formula of Fredlund-Xing model. At the same time, the expansion force formula of an initial expansive soil is obtained under the condition of arbitrary change of saturation.
【学位授予单位】：桂林理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU443

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