非饱和土水特征曲线的温度效应研究

发布时间：2018-07-15 09:19

【摘要】：非饱和土水特征曲线通常定义为土中基质吸力s（kPa）与重力含水量w或体积含水量θ、饱和度S之间的关系。它反映了土壤的储水和释水性质，与孔隙结构和孔径分布密切相关，可以用于预测非饱和渗透性函数、抗剪强度等物理和力学参数，，因此在非饱和土力学中有着非常重要的意义。影响土水特征曲线的因素有很多，如滞回性、液体粘滞性影响、应力状态影响、应力历史影响、颗粒级配等，这些因素对土壤的持水能力影响很大，因而引起了众多学者的关注。相比较而言，自然环境中温度的变化是不大的，其对土壤持水能力的影响体现得并不显著，所以往往被忽视。但随着科学技术的不断进步，岩土工程领域所涉及的问题越来越复杂，如地下核废料的处置、二氧化碳地下封存、地热资源开发、石油开采、高压电缆的埋设等，更多的工程设施将承受较大的温度变化。此时，温度对土水特征曲线的影响变得不可忽略。目前，对于如何获取考虑温度影响的土水特征曲线以及其影响机理，学者们还没有达成一致意见。本研究开发了一套高精度土水特征曲线自动测试系统，开展了不同温度作用下粉土质砂土水特征曲线试验，讨论和分析了温度影响下非饱和土水特征曲线的变化规律及温度的作用机制，并建立了考虑温度影响的土水特征曲线预测模型，进行了一维土柱非饱和土蒸发试验与数值分析。研究的主要内容及结论如下： 1）研制了一套高精度土水特征曲线自动测试系统。该系统实现了整个测试过程的全自动化控制，同时提高了气压力控制精度、修正了每一级气压下排水体积量和实现了对试验温度的控制，在满足特定试验需求的同时提高了试验效率和保证了试验的精度，特别适用于粗颗粒土的相关试验测试。为了实现仪器的规范化操作，还特别编制了仪器的操作规程，介绍了仪器操作注意事项，为后续试验提供了技术支持。 2）将高精度土水特征曲线自动测试系统置于温控箱中，开展了4种不同温度作用下粉土质砂的土水特征曲线试验，并与其他学者的相关试验数据对比，讨论和分析了温度影响下非饱和土水特征曲线的变化规律及温度的作用机制。结果表明，温度对非饱和土水特征曲线的影响不可忽略，随着温度的升高土壤的进气值和残余含水量均在减小，基质吸力相同时，土壤的体积含水量随温度上升逐渐减小，土壤颗粒大小和孔隙尺寸分布的不同导致温度对粉土质砂、粉质土、粘性土和膨胀土的土水特征曲线的影响出现局部的差异性。 3）以热力学及非饱和土相关理论为基础，考虑表面张力、浸润角和吸力的温度效应，借助于van Genuchten模型，在分析研究模型中各参数随温度变化规律的同时建立了考虑温度影响的土水特征曲线预测模型。通过将预测结果与实测数据进行对比可以发现该模型具有较好的适用性。对于粘粒含量较大的土，由于忽略了温度对颗粒表面水合作用的影响，在基质吸力大于进气值的区段，预测结果与实测结果存在一定的偏差。 4）研制了可变环境条件自动蒸渗测量系统，开展了一维土柱室内蒸发试验，同时采用非饱和土水-热迁移方程及相关预测参数对蒸发条件下土壤水分的运动进行了数值模拟，最后将数值计算结果与实测试验结果进行对比，检验了水-热迁移方程及相关预测参数的可靠性。结果表明，非饱和土的蒸发过程可分为三个阶段：稳定阶段、减速阶段、残余阶段。随着蒸发的持续进行，土柱纵剖面上含水量开始出现明显的梯度，干-湿界面从土表开始形成并随着蒸发的进行不断向下推移。数值计算结果与实测值基本吻合，说明该计算模型及相关参数的选取是合理的，所得的结论是可靠的。论文创新点：开展了考虑温度影响的非饱和土水特征曲线试验研究，并进行了影响机理分析；建立了考虑温度影响的土水特征曲线预测模型，并应用于蒸发条件下土壤水分运动的数值模拟研究。
[Abstract]:The characteristic curve of unsaturated soil water is usually defined as the relationship between matrix suction s (kPa) and gravity water content w or volumetric water content [theta] and saturation S. It reflects soil water storage and water release properties, closely related to pore structure and pore size distribution, and can be used to predict unsaturated permeability function, shear strength and other physical and mechanical parameters. Therefore, there are very important significance in the mechanics of unsaturated soil. There are many factors affecting the soil water characteristic curve, such as hysteresis, the influence of liquid viscosity, stress state, stress history and particle gradation. These factors have great influence on the water holding capacity of the soil, so many scholars pay attention to it. The change in temperature is not significant in the environment, and its influence on soil water holding capacity is not obvious, so it is often ignored. But with the continuous progress of science and technology, the problems involved in the field of geotechnical engineering are becoming more and more complex, such as the disposal of underground nuclear waste, the underground seal of carbon dioxide, the development of geothermal resources, the exploitation of oil, the high voltage electricity. At this time, the influence of temperature on the soil water characteristic curve can not be ignored. At present, there is no agreement on how to obtain the soil water characteristic curve and its influence mechanism.
An automatic test system for high precision soil water characteristic curve is developed in this study. The water characteristic curve of silty soil under different temperatures is carried out. The variation law of unsaturated soil water characteristic curve and the mechanism of temperature effect under the influence of temperature are discussed and analyzed, and the prediction model of soil water characteristic curve with the influence of temperature is established. The evaporation test and numerical analysis of unsaturated soil in one dimension soil column are carried out. The main contents and conclusions are as follows:
1) a set of automatic test system for high precision soil water characteristic curve is developed. The system realizes full automation control of the whole test process, improves the control precision of pressure force, corrections the volume of drainage under each air pressure and realizes the control of the test temperature, and improves the test efficiency while meeting the specific test demand. The accuracy of the test is guaranteed. It is especially suitable for the test of coarse granular soil. In order to realize the standardized operation of the instrument, the operating regulations of the instrument are specially compiled, and the precautions for the operation of the instrument are introduced, and the technical support for the follow-up test is provided.
2) the automatic test system of high precision soil water characteristic curve is placed in the temperature control box, and the soil water characteristic curve of 4 kinds of silty sand under different temperatures is carried out. And compared with the related experimental data of other scholars, the change law of the characteristic curve of unsaturated soil water and the mechanism of temperature are discussed and analyzed under the influence of temperature. The influence of temperature on the characteristic curve of unsaturated soil water can not be ignored. With the increase of temperature, the intake and residual water content of soil decreased, and the volume of soil volume decreased with the temperature, and the size of soil particles and the distribution of pore size resulted in the temperature on silty sand, silty soil and stickiness. The influence of soil water characteristic curve of soil and expansive soil is local difference.
3) on the basis of the theory of thermodynamics and unsaturated soil, the temperature effect of surface tension, infiltration angle and suction is considered. With the help of van Genuchten model, the prediction model of soil water characteristic curve with the influence of temperature is established at the same time, and the prediction results are carried out with the measured data. The comparison can be found that the model has good applicability. For clay with larger clay content, there is a certain deviation between the predicted result and the measured result because of neglecting the effect of temperature on the hydration of the particle surface, and in the section of the matrix suction greater than the intake value.
4) the automatic vaporization measurement system with variable environment conditions was developed, and the indoor evaporation test of one dimension soil column was carried out. At the same time, the numerical simulation of soil moisture movement under the evaporation condition was simulated with the unsaturated soil water heat transfer equation and the related prediction parameters. Finally, the numerical results were compared with the experimental results, and the water heat migration was tested. The stability of the evaporation process of the unsaturated soil shows that the evaporation process of the unsaturated soil can be divided into three stages: the stable stage, the deceleration stage and the residual stage. With the continuous evaporation of the soil, the water content in the vertical section of the soil column begins to appear obvious gradient, the dry wet interface begins to form from the soil surface and continues down with the evaporation. The numerical results are basically consistent with the measured values, indicating that the calculation model and the selection of relevant parameters are reasonable, and the conclusions obtained are reliable.
The innovation points of this paper are as follows: the experimental study of unsaturated soil water characteristic curve with the influence of temperature is carried out, and the influence mechanism is analyzed. The prediction model of soil water characteristic curve with the influence of temperature is established and applied to the numerical simulation of soil water movement under the condition of evaporation.
【学位授予单位】：三峡大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU43

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