软土地基电渗加固方法研究

发布时间：2018-09-12 18:25

【摘要】：电渗加固技术可以对高含水量、低渗透性的软粘土进行高效快速的排水固结,具有广泛的应用前景。本文总结了电渗加固技术的研究现状,开展电渗固结模型试验,深入了解软土地基电渗固结的宏观规律和微观特性;完善电渗固结理论模型,发展数值计算方法,促进电渗固结技术的推广应用。建立一套电渗加固模型试验系统,实时监测土体电渗加固过程中的宏观物理量时空变化,对电渗前后的土样测量分析其物理化学性质、测试其微观结构和矿物成分变化特性。实时监测的物理量包括出水量、电势、电流、土体位移、p H值等;测试分析的土体特性包括含水量、液塑限、自由膨胀率、zeta电位、阳离子交换量,以及微观结构、化学成分和矿物成分。电渗加固模型试验表明初始含水量和电极材料影响电渗排水过程,电渗作用会改变土体物理化学性质。高岭土的电渗试验结果说明,初始含水量越高,最终排水比例越大,间歇通电效果越明显。钠基膨润土的试验结果表明,活性电极的电渗排水效果比惰性电极好,电渗作用使得阳极处膨润土的塑性指数和自由膨胀率减小,可以有效抑制膨润土的胀缩特性。微观测试表明电渗过程导致膨润土微观结构和矿物成分发生显著变化,是其物理化学性质改变的根本原因。电渗后,阳极附近膨润土样的微观结构从絮状结构变为颗粒堆积结构,孔隙比减小,土样更加密实;粘土颗粒表面双电层中和晶层内的钠离子被替换,导致双电层厚度减小,晶层间联结力增强。这些微观特性的改变进一步导致粘土颗粒吸水能力减弱,因此塑性指数和自由膨胀率减小。试验结果同时说明,钠离子是钠基膨润土电渗排水过程中最主要的微观作用离子。发展和完善考虑土体参数非线性变化的多场耦合理论,反映土体电渗固结过程中渗流场、应力位移场和电场的时空变化特征。研究简化模型的解析理论,推导得到孔压和固结度的解析表达式,提出沉降计算公式,绘制电极间距、沉降和土体电渗参数之间的关系图,可用于指导工程设计。发展数值计算模型,与解析理论和试验结果对比验证其合理性;利用该数值模型,针对复杂工况问题和工程实例进行计算分析,结果表明该模型能合理描述土体电渗固结过程中位移、孔压、应力等物理量的发展变化过程。
[Abstract]:Electroosmotic reinforcement technology can be used for high water content and low permeability soft clay for high efficiency and fast drainage consolidation, which has a wide application prospect. In this paper, the research status of electroosmotic consolidation technology is summarized, the electroosmotic consolidation model test is carried out, the macroscopic and microscopic characteristics of electroosmotic consolidation of soft soil are deeply understood, the theoretical model of electroosmotic consolidation is improved, and the numerical calculation method is developed. To promote the popularization and application of electroosmotic consolidation technology. A set of electroosmotic reinforcement model test system was set up to monitor the time and space change of macroscopic physical quantity in the process of soil electroosmotic reinforcement in real time. The physical and chemical properties of soil samples before and after electroosmosis were measured and their microstructure and mineral composition characteristics were tested. The physical parameters of real-time monitoring include water output, electric potential, current, soil displacement and pH value, etc. The soil properties measured and analyzed include water content, liquid plastic limit, free expansion rate and Zeta potential, cation exchange capacity, and microstructure. Chemical and mineral composition. The model test of electroosmotic reinforcement shows that the initial water content and electrode material affect the process of electroosmotic drainage and the electroosmotic effect will change the physical and chemical properties of soil. The results of electroosmotic test of kaolin show that the higher the initial water content, the larger the final drainage ratio, and the more obvious the intermittent electrification effect is. The experimental results of sodium bentonite show that the electroosmotic drainage effect of the active electrode is better than that of the inert electrode, and the plastic index and the free expansion rate of the bentonite at the anode can be reduced by the electroosmotic action, which can effectively inhibit the swelling and shrinkage characteristics of the bentonite. Microscopic tests show that the electroosmotic process leads to significant changes in microstructure and mineral composition of bentonite, which is the fundamental reason for the change of physical and chemical properties of bentonite. After electroosmosis, the microstructure of bentonite samples near the anode changed from flocculent structure to granular stacking structure, the porosity ratio decreased and the soil sample became more dense, and the sodium ions in the double electric layer and the crystal layer on the surface of clay particles were replaced, which resulted in the decrease of the thickness of the double electric layer. The intergranular bonding force is enhanced. The changes of these microscopic properties further weaken the water absorption ability of clay particles, so the plasticity index and free expansion ratio decrease. The results also show that sodium ion is the most important microcosmic ion in the electroosmotic drainage process of sodium bentonite. The multi-field coupling theory, which takes into account the nonlinear variation of soil parameters, is developed and perfected to reflect the space-time variation characteristics of seepage field, stress-displacement field and electric field in the process of soil electroosmotic consolidation. The analytical theory of the simplified model is studied and the analytical expressions of pore pressure and degree of consolidation are derived. The calculation formula of settlement is put forward, and the relationship diagram between electrode spacing, settlement and electroosmotic parameters of soil is drawn, which can be used to guide engineering design. The numerical calculation model is developed and compared with the analytical theory and experimental results to verify its rationality, and the numerical model is used to calculate and analyze the complex working conditions and engineering examples. The results show that the model can reasonably describe the development of displacement, pore pressure and stress in the process of soil electroosmotic consolidation.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU472

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