【作者】 李瑛；

【导师】 龚晓南；

【作者基本信息】 浙江大学 ， 岩土工程， 2011， 博士

【摘要】 传统的重力排水固结方法在处理低渗透性黏土时费时长久,有时甚至难以达到预期目的。性质更差的吹填淤泥和疏浚淤泥给地基处理方法带来新的挑战。在众多地基处理新方法中,电渗排水固结是较有前途的一种,因为其排水速率与土颗粒大小无关。然而,固结机理的不完善、设计计算方法的欠缺、能量消耗过高等原因制约了电渗的工程应用,因此有必要开展软黏土电渗固结的进一步研究。首先,开展三种不同条件下的电渗固结室内试验研究,以完善电渗固结机理。通过室内一维电渗固结试验研究分析了电压和土体含盐量对电渗固结的影响；提高电压能够加速电渗排水,但会导致排出单位体积水所消耗的能量增加；土体含盐量对电渗有很大影响,在适宜含盐量的软黏土地基中进行电渗能够以最低的能量消耗取得最好的处理效果。通过室内二维电渗固结试验研究分析了电势梯度相等时电极间距对电渗固结的影响,揭示了电渗过程中和电渗后黏土性质在电极之间的平面分布；减小电极间距可明显提高电渗固结效果,但是会导致电化学反应量的增大；在电渗固结过程中,黏土逐渐从饱和状态变化到非饱和状态,土体裂缝不断增多。室内轴对称电渗固结试验研究显示电极间的电势分布是通电时间和径向距离的函数。而且通过三种不同条件的电渗固结试验结果的对比分析发现电极形式对电渗固结影响的关键在于损失在电极和土体接触面上的电压与两极之间电压的比值。然后,开展二维电渗电场强度计算的理论研究。基于土体均匀各向同性假设和忽略电极截面尺寸影响,推导出电极长方形布置下的电场强度计算式,并根据参数分析结果对水平向电场分解和简化。水平电场在异性电极连线方向上的分量可简化为均匀的,电场强度可用相邻两对电极所围区域中心处的电场强度表示；同性电极连线方向上的水平电场分量包括有效部分和无效部分,无效部分在相邻两对电极间的平面范围为两个以同性电极间距为底边以一半同性电极间距为高的等腰三角形。接着,进行电渗固结理论的解析研究。利用等应变假设和实测的电势分布,从电流和水流耦合出发,建立轴对称电渗固结理论,推导出地基中径向平均孔压和按应力定义的径向平均固结度的解答,并提供电极梅花形布置向轴对称的环形布置的转换方法。参数分析表明：电极轴对称布置时施加的电压越高径向孔压消散得越快；电渗渗透系数与水力传导系数的比值在一定范围内电渗固结快速又经济。最后,以降低电渗能耗为目的进行软黏土地基电渗固结设计方法研究。在归纳总结软黏土电渗固结各影响因素后,提出软黏土地基电渗固结设计方法,相比已有方法增加了地基电渗适宜性评价和电渗系统参数优化,工程实例表明该方法能有效提高电渗效果和效率。本文的工作有助于电渗固结在软黏土地基处理中的应用和研究。更多还原

【Abstract】 It takes a long time and even is difficult to improve low conductivity clay with conventional gravitational drainage methods based on mechanics such as vacuum preloading and preloading. Challenge is increasing while soft foundation was formed more and more by hydraulic filling recently. Compared with natural clay, dredger fill or dredged sediment has larger compressibility and smaller undrained shear strength. In the advances of ground improvement technologies electro-osmotic consolidation is much promising because its drainage rate is independent of clay particle size. However, the application of this method was limited by consolidation mechanism, design and calculating, energy demand and others. Research program was implemented to study electro-osmotic consolidation of soft clay.Electro-osmotic experiments program in the three different electrodes arraies was conducted in the laboratory firstly. The effect of supply voltage and soil salinity to electro-osmosis was studied through one-dimensional laboratory tests. Larger voltage leads faster drainage and lower energy efficiency. Clay salinity had a significant effect on the electro-osmotic consolidation. Consolidation in the feasible salty ground could gain the best result by the lowest energy consumption. Two-dimensional laboratory tests were conducted to reveal the effect of electrodes spacing to consolidation and the variation of clay properties in the space and time during dealing. Halving the spacing while keeping voltage gradient constant could enhance consolidation evidently. Saturated stage of clay was transformed gradually to unsaturated stage by electro-osmosis. The wettest part after testing might be between anode and cathode. Voltage profiles between annular electrodes were measured in the axisymmetric experiments and were proved to be dependent of dealing time and radial distance. The difference caused by electrodes shapes to consolidation was obtained after comparing tests under three different conditions. Voltage drop in the contact of soil and electrode varied with electrode shape and each shape had its strong point.Then the caiculation of electric field among electro-osmotic electrodes was studied. The calculated formula of electric field intensity among electrodes arrayed rectangular was proposed based on the assumption of homogeneous isotropic soil and ignoring the sectional dimensions of electrodes. Horizontal electric field intensity was decomposed and simplified considering the effect of adjacent electrodes. The intensity in the direction parallel to the beeline through anode and corresponding cathode could be assumed to even and the value equaled to the intensity in the centre of rectangle while the one perpendicular to it included effective part and ineffective part which was two isosceles triangles with the base being the distance between electrodes of the same polarity and the height being half its base.Then the consolidation theory of electro-osmosis was analyted. According to the voltage profile measured in the axisymmetric experiments, axisymmetric electro-osmotic consolidation theory was established base on the equal strain assumption and related theories which already existed. The analytic solutions for average excess pore pressure and radial average degree of consolidation in terms of stress were provided and so did the method of conversion from hexagonal array of electrodes to axisymmetric array. This theory could incorporate the coupling action of electro-osmosis and loading and the effect of soil-electrode contact. The results of parametric analysis showed that better consolidation effect can be gained by higher supply voltage and there was a range of appropriate ratio of electro-osmosis permeability coefficient to hydraulic permeability coefficient for axisymmetric electro-osmotic consolidation.The design method of electro-osmotic consolidation of soft clay foundation was suggested at last. An ameliorated design method of electro-osmotic consolidation of soft clay foundation was proposed after investigating the collected data and summarizing the influence factors of electro-osmotic consolidation finally. The difference between the method and existed ones was that the electro-osmotic treatment acceptability of sites was evaluated before calculating and electro-osmotic system parameters could be optimized during selecting. Evaluation and optimization can be finished easily using the tables offered. A classical case history was illustrated to confirm that this design method lead electro-osmotic consolidation to be more effective and more efficient.The present work would be useful to promote the application and research of electro-osmotic consolidation of soft clay foundation.更多还原