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基于电导率计算的黏土电渗离子迁移与含盐量时空分布特性
Ionic Migration and Spatiotemporal Distribution Characteristics of Salinity in Clay Using Electro-osmosis Based on Conductivity
在电渗排水过程中,黏土中的可溶性盐在电场作用下发生迁移。为研究电渗过程中可溶性盐的时空分布及其对排水效率的影响,开展了电导率试验,利用土体电导率建立了含盐量的计算公式。在一维电渗固结试验中,监测了分区电压、电导率、排水量和电流,反演了土体含盐量的变化及离子迁移趋势。试验结果表明,电导率受含盐量与含水量的共同影响,且含盐量的影响更为显著。电渗过程中,阳极区域含盐量变化较小,中间区域先上升后下降,阴极区域则快速下降,电渗结束时含盐量从阳极到阴极依次递减。电渗排水法不仅能加速黏土的排水固结,还能有效排除土中的可溶性盐,减少高含盐量对后续施工的影响,为处理高含盐土体提供了新思路。
[Objective] This study investigates how soluble salts in clay redistribute under an applied direct-current electric field during electro-osmotic drainage and how the redistribution affects dewatering and consolidation efficiency. The study quantifies the spatiotemporal evolution of salt content through bulk electrical conductivity, distinguishes the individual effects of salinity and water content on conductivity, and infers ion-migration trends and their implications for the combined dewatering and desalination performance of saline clays. [Methods] Laboratory conductivity calibrations were conducted on remolded clay across practical ranges of water content and soluble-salt concentration. Based on these data, an empirical relationship was established that linked soil bulk conductivity to pore-fluid salinity while explicitly incorporating water content, enabling the conversion of measured conductivities into estimates of salt content. Subsequently, a one-dimensional electro-osmotic consolidation test was conducted. Segmented voltage, local conductivity, cumulative drainage, and current were monitored and recorded. Using this calibration, time-lapse conductivity profiles were processed to reconstruct salt-content distributions and their evolution. This method could provide a framework to monitor and interpret coupled ionic transport and water removal during electro-osmosis. [Results] Calibration showed that conductivity increased with both salinity and water content. However, when water content was considered, salinity accounted for a larger share of the variance in bulk conductivity. Accordingly, conductivity served as a reliable in-situ indicator of salt content during electro-osmosis. The electro-osmotic test revealed a distinct zonation of salt content consistent with electromigration toward the cathode. At the anode, salt content declined rapidly during the first 2 hours and then stabilized at approximately 2.0 g/L until the end of the test. In the mid-section, salt content also decreased over the first 2 hours, showing the smallest reduction among the three regions, followed by an increase and subsequent decline. By 6 hours, it temporarily exceeded the initial salinity. This peak reflected the convergence in the middle zone of cation fluxes migrating from anode to cathode and anion fluxes moving in the opposite direction. After 6 hours, the mid-section salinity decreased progressively and, at the end of the test, fell below that of the anode region. The cathode experienced the most pronounced change, showing a continuous decline throughout energization. By 8 hours, the cathodic zone had nearly approached a salt-free state. During electro-osmosis, the soil potential field was strongly modulated by both water content and salinity, producing spatially differentiated potential distributions that evolved over time. Water content and drainage rate exhibited non-uniform dynamics among regions and ultimately formed a moisture gradient of Anode < Middle < Cathode. Salinity exerted a pronounced control on potential pathways and transmission efficiency. Therefore, its evolution should be incorporated explicitly in design to optimize treatment outcomes. The combined evidence demonstrated that electro-osmotic drainage in saline clay could achieve two outcomes simultaneously: accelerated consolidation and effective removal of soluble salts. The latter mitigated adverse effects of high salinity on subsequent construction, including corrosion risk and strength variability, thereby improving the suitability of the treated ground. [Conclusion] This study delineates the migration and distribution patterns of soluble salts in high-salinity clays under electro-osmotic drainage, offering a new perspective for treatment and practical guidance for engineering application. Operationally, a critical point is reached when salinity in the cathodic zone drops to a very low level. Continuing energization beyond this point leads to sharply diminished drainage efficiency and disproportionately increased energy consumption. At the design stage, measuring soil electrical conductivity and conducting pre-tests to characterize the salinity-moisture relationship are recommended, thereby informing the required energization time. In practice, continuous conductivity monitoring provides a comprehensive indicator of overall dewatering progress. Wider adoption of these insights is expected to facilitate broader and more effective application of electro-osmosis in geotechnical engineering.
clay / electro-osmosis / salinity / conductivity / ground treatment
| [1] |
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| [2] |
Electro-osmosis and ionic migration are the basic cleanup mechanisms in the electrokinetic extraction of contaminants from fine-grained soils. These are coupled flows as the flows of fluid and contaminants are driven by an externally applied electrical gradient. Moreover, other electrochemical reactions will occur simultaneously during the process. The most pronounced effect is the generation of pH gradient in the soil. The change of pH in the pore fluid can have a significant impact on the degree of sorption and desorption of chemicals on soil particle surfaces, complexes formation and precipitation of chemical species, and dissociation of organic acids; thus affecting the feasibility and efficiency of the cleanup technique tremendously. An attempt is made to formulate the coupled flows of ionic contaminants and the resulting change of pH in the pore fluid during the electrokinetic extraction process. The coupled flows of contaminants are formulated by the formalism of nonequilibrium thermodynamics. The pH is determined as a function of time and space by maintaining electrical neutrality throughout the system all the times. A numerical model NEUTRAL is developed to simulate the processes. The good agreement between computed and experimental results published in the literature indicates that the approach is a valid step toward a better understanding of the physics and chemistry involved during electrokinetic treatment of contaminated soils. Key words : electrokinetics, in situ remediation, contaminated soil, coupled flows, electrochemistry, nonequilibrium thermodynamics.
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| [3] |
黄文聪, 李广, 罗沈, 等. 电势梯度对软土电渗固结效果及能耗分析试验研究[J/OL]. 长江科学院院报.(2024-01-08)[2024-05-31]..
(
|
| [4] |
周子健, 钟方涛, 齐昌广, 等. 竖向电渗增强桩承载理论及试验验证[J]. 地基处理, 2023, 5(3): 181-186, 204.
(
|
| [5] |
赵洪星. 电渗联合化学溶液加固淤泥质软土试验研究[J]. 长江科学院院报, 2022, 39(5): 99-105.
采用自制室内试验装置,研究电渗联合化学溶液对淤泥质软土的排水固结效果。通过对比分析电流值、电渗排水量、抗剪强度和微观结构等方面的差异,进一步揭示了不同化学溶液对电渗固结效果的影响机理。试验结果表明:化学溶液的加入可以促进电渗排水,而小原子量、低价态离子的促进效果更为显著,在本次试验中Na<sup>+</sup>>Ca<sup>2+</sup>>Al<sup>3+</sup>;运动到阴极附近的Ca<sup>2+</sup>、Al<sup>3+</sup>离子可以参与反应生成胶结物质,增强了土颗粒间的黏结力,提高了阴极土体的抗剪强度,其中以Ca<sup>2+</sup>离子增强效果最明显,土体抗剪强度提高了3.5倍;而化学溶液的加入则会加速电极腐蚀和土体的酸碱化。
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A one-dimensional laboratory test program is performed to investigate the strengthening effect of electroosmosis incorporated anolyte on mucky clay. By comparing the differences in electroosmotic current, drainage, shear strength and microstructure of soil, the mechanism of various anolyte accelerating the electroosmotic dewatering is further revealed. The testing results show that the injection of chemical solution facilitates the electrochemical drainage. Cations with lower atomic weight and valence have more significant effect: Na<sup>+</sup>>Ca<sup>2+</sup>>Al<sup>3+</sup>. The Ca<sup>2+</sup> and Al<sup>3+</sup> cations migrated to cathodic region react with hydroxyl ion to produce cementing agent, which enhances the cohesion between soil particles and improves soil's shear strength. Ca<sup>2+</sup> has the strongest improvement effect by enhancing the shear strength of the cathodic soil by as much as 350%. Moreover, the injection of chemical solutions will also accelerate electrode corrosion and induce larger variation of pH value.
|
| [6] |
吴松华. 不同形式电渗加固吹填淤泥现场试验研究[J]. 长江科学院院报, 2020, 37(5): 108-112.
为了研究电渗法加固吹填淤泥的实际效果,同时了解电极布置形式对电渗加固效果的影响,依托具体吹填项目,采用无砂垫层真空预压联合电渗(S1)、无砂垫层真空预压联合电渗注浆(S2)和无砂垫层真空预压联合导电排水板(S3)3种类型大试验,并将S1和S3的电极分平行和错位间隔2种方式布置,现场进行5种对比小试验并对加固效果进行分析。通过分析试验数据得到:5种试验和无砂垫层真空预压法相比,土体加固后的地基承载力和抗剪强度等指标均有较大提高,土体含水率均有较大程度的降低。试验结果表明:无砂垫层真空预压联合电渗法加固地基效果比无砂垫层真空预压法好、工期短;采用真空预压联合电渗注浆(S2)比其它几种形式加固效果要好。无砂垫层真空预压联合电渗法可有效弥补无砂垫层真空预压法的一些不足,适用于对承载力和工期等有特殊要求的吹填土地基加固工程。
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In order to investigate the practical effect of electroosmosis method in reinforcing dredger-fill silt and in the meantime to understand the influence of electrode arrangement on the reinforcement effect, we performed three types of test based upon specific dredger-fill projects. These tests include vacuum preloading without sand cushion combined with electroosmosis (hereafter referred to as S1), vacuum preloading without sand cushion combined with electroosmosis grouting (S2), and vacuum preloading without sand cushion combined with conductive drainage plate (S3). Moreover, both in S1 and S3, the electrodes were arranged in parallel and dislocated intervals, respectively. Thus, in total we conducted five tests for comparative study. The test data shows that the bearing capacity and shear strength of the foundation strengthened by the five tests have been greatly improved, and the water content of the soil has been greatly reduced. The results demonstrate that the effect of S1 is better than that of vacuum preloading without sand cushion, with shorter construction period. The effect of S2 is better than that of other test forms. Electroosmosis method combined with vacuum preloading without sand cushion could effectively remedy some shortcomings of vacuum preloading without sand cushion, and can be applied to consolidation of dredger-fill foundation with special requirements for bearing capacity and duration.
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| [7] |
刘飞禹, 吴文清, 海钧, 等. 絮凝剂对电渗处理河道疏浚淤泥的影响[J]. 中国公路学报, 2020, 33(2): 56-63, 72.
河道疏浚淤泥含水量高，流动性大，运输和处置较难，且易对环境造成二次污染，需要对其进行脱水处理，而且脱水后的疏浚淤泥可以作为道路路基的主要填充材料，提高资源利用率。因此为了更好地提高疏浚淤泥的脱水效果，利用自制的电渗试验装置，对疏浚淤泥进行了无机絮凝剂电渗排水试验。先将疏浚淤泥进行初步脱水，使其含水量保持在75%左右，作为待用土样；再根据无机絮凝剂FeCl<sub>3</sub>和Al<sub>2</sub>（SO<sub>4</sub>）<sub>3</sub>的不同掺入比配制溶液，与待用土样充分混合，静置24 h后装填土样启动电渗试验。电渗过程中监测排水量和电流强度，试验后测量土体的含水量和pH。试验结果表明：絮凝剂对疏浚淤泥电渗排水效果有着明显的影响，并存在最佳掺入比使得排水效果最好，其中FeCl<sub>3</sub>与Al<sub>2</sub>（SO<sub>4</sub>）<sub>3</sub>的最佳掺入比均为0.1%；当掺入比高于最佳值时，将会降低电渗排水效果；与纯电渗试验相比，随着絮凝剂掺入比的增大，电流会增大，电渗能耗也随之增大；试验后，土体的含水量有明显降低但分布不均，主要表现在FeCl<sub>3</sub>作用时阳极区域高于阴极区域，而对照组和Al<sub>2</sub>（SO<sub>4</sub>）<sub>3</sub>作用时阴极区域优于阳极区域；由于试验过程中絮凝剂的水解以及电化学反应，在试验前后土体均保持酸性，且随着絮凝剂掺入比的增加，土体pH会随之降低，电导率会随之增加。
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River-dredged sludge is characterized by a high water content and great fluidity. Its transport and disposal are difficult, and this may easily lead to secondary pollution of the environment. It therefore appears necessary to dewater the sludge prior its transport and disposal. Moreover, if properly treated, the sludge could easily be used as the main filling material in road construction, thereby optimizing the utilization of resources. In order to improve the drainage of the dredged sludge, a series of tests were carried out-using a self-made electro-osmotic test device-in which electro-osmosis and the use of inorganic flocculants were combined. Firstly, the dredged sludge was preliminarily drained to reach 75% used as the soil sample. Then, FeCl<sub>3</sub> and Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> were mixed with the soil in different proportions to promote flocculation. After 24 hours, electro-osmosis was performed, and the amount of water drained and the current intensity were monitored. The results showed a significant influence of the flocculant on the electro-osmotic drainage of the sludge. The optimal mixing ratios of both FeCl<sub>3</sub> and Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> were found to be 0.1%. Higher-than-optimal ratios were found to reduce the effect of the electro-osmotic drainage. Compared with electro-osmosis in absence of flocculant, the electric current and energy consumption were found to increase with the mixing ratio increasing. After the tests, the water content of the soil was found to have decreased significantly; however, the spatial distribution of such decrease was uneven, as it mainly occurred in the anode region in the case of FeCl<sub>3</sub>, and in the cathode region in the case of Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>. Due to the hydrolysis of the flocculant and electrochemical reactions, the soil remained acidic before and after the tests. With the mixing ratio increasing, the pH of the soil decreased, while the conductivity increased.
|
| [8] |
周建, 蒋熠诚, 朱则铭, 等. 电渗加固软土地基界面电阻理论与试验研究[J]. 岩土工程学报, 2023, 45(10):1995-2003.
(
|
| [9] |
李瑛, 龚晓南. 含盐量对软黏土电渗排水影响的试验研究[J]. 岩土工程学报, 2011, 33(8):1254-1259.
(
|
| [10] |
张雷, 王宁伟, 景立平, 等. 电渗排水固结中电极材料的对比试验[J]. 岩土力学, 2019, 40(9): 3493-3501, 3514.
(
|
| [11] |
罗战友, 陶燕丽, 周建, 等. 杭州淤泥质土的电渗电导率特性研究[J]. 岩石力学与工程学报, 2019, 38(增刊1): 3222-3228.
(
|
| [12] |
焦丹, 任芮花, 王铁行, 等. 土壤含盐量对电势作用下黄土水分迁移影响试验研究[J]. 中南大学学报(自然科学版), 2019, 50(12): 3075-3083.
(
|
| [13] |
Electrokinetic consolidation is an innovative method for ground improvement in special conditions such as underwater construction. This method uses a weak electromagnetic field to dewater weak soils or slurries. Due to their chemical structure, water molecules act as dipoles, where the positive charge has a larger spatial distribution. Hence, when a low voltage is applied, water moves towards the cathode and can be drained there. Most current experimental studies in laboratories often use pure water, whereas weak soils located offshore or near the coastal line are often saline. It is not understood for saline soil whether a small zeta potential decreases efficacy or electromigration may reverse the negative effect. This paper presents an experimental research study on the influence of salinity on the efficacy of electrokinetic consolidation methods. The work reported herein suggests that the coefficient of consolidation increases linearly with salinity. The higher the salinity, the faster the consolidation. A salinity of 40 g/l can make the consolidation process six times faster.
|
| [14] |
|
| [15] |
陶燕丽, 周建, 龚晓南, 等. 基于杭州软土的电渗迁移过程试验研究[J]. 中南大学学报(自然科学版), 2018, 49(2):448-453.
(
|
| [16] |
|
| [17] |
储亚, 刘松玉, 蔡国军, 等. 岩土体电阻率模型研究进展[J]. 南京工程学院学报(自然科学版), 2017, 15(2):1-9.
(
|
| [18] |
甘淇匀. 软土电渗的电场作用机理与多场耦合理论研究[D]. 杭州: 浙江大学, 2022.
(
|
| [19] |
储亚, 刘松玉, 蔡国军, 等. 重金属污染黏性土电阻率影响因素分析及其预测模型[J]. 东南大学学报(自然科学版), 2016, 46(4):866-871.
(
|
| [20] |
储亚, 刘松玉, 徐磊, 等. 膨润土-高岭土混合介质的表面电导率研究[J]. 土木工程学报, 2019, 52(增刊2):23-29.
(
|
| [21] |
柴寿喜, 王晓燕, 仲晓梅, 等. 含盐量对石灰固化滨海盐渍土稠度和击实性能的影响[J]. 岩土力学, 2008, 29(11): 3066-3070.
(
|
| [22] |
|
| [23] |
邱晨辰, 沈扬, 励彦德, 等. EKG电极真空-电渗处理软黏土室内试验研究[J]. 岩土工程学报, 2017, 39(增刊1): 251-255.
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