Numerical solution for contaminant transport in cutoff wall considering semipermeable membrane behavior

doi:10.3785/j.issn.1008-973X.2025.02.012

Journal of ZheJiang University (Engineering Science)

2025, Vol. 59

Issue (2): 342-350 DOI: 10.3785/j.issn.1008-973X.2025.02.012

Numerical solution for contaminant transport in cutoff wall considering semipermeable membrane behavior

Shengyi DENG1(

),Yongwei ZHOU3,Hefu PU1,2,*(

),Yuchao LI4,Ming MIN1

1. School of Civil and Hydraulic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
2. College of Civil and Transportation Engineering, Shenzhen University, Shenzhen 518061, China
3. Hubei Dijian Construction Limited Company, Wuhan 430050, China
4. Key Laboratory of Soils and Geoenvironmental Engineering, Ministry ofEducation, Zhejiang University, Hangzhou 310058, China

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Abstract

A numerical model was proposed for contaminant transport in bentonite-based cutoff wall-aquifer system, considering the semipermeable membrane behavior, and the finite difference method was used to obtain the solution. The effectiveness of the numerical solution was validated against the existing analytical solution, semipermeable membrane experiment and COMSOL software simulation. Parametric analyses were conducted using the proposed numerical solution, and the effects of semipermeable membrane behavior, contaminant source mass concentration, thickness of cutoff wall, hydraulic conductivity of cutoff wall, and hydraulic gradient on the transport of lead in the cutoff wall-aquifer system were analyzed. Results show that the semipermeable membrane behavior has a significant impact on contaminant transport, and neglecting this effect can lead to a great underestimation of the breakthrough time and an overestimation of outflow mass flux. Incorporating the semipermeable membrane behavior increases the breakthrough time by 12.2% to 79.6% and decreases the mass flux by 18.4% to 62.3% for the various analyzed conditions. Mass flux reduces by 2 orders of magnitude, and the difference between considering and neglecting semipermeable membrane behavior increases from 31.1% to 97.5% for hydraulic conductivity decreasing from 1×10^?8 m/s to 1×10^?10 m/s. The proposed numerical solution can consider the effects of advection, molecular diffusion, mechanical dispersion, semipermeable membrane behavior and effective porosity, which can be used in design of bentonite-based cutoff wall and the associated analysis of contaminant transport process.

Key words： cutoff wall contaminant transport semipermeable membrane behavior

Received: 18 December 2023 Published: 11 February 2025

CLC:

TU 443

Fund: 国家重点研发计划资助项目（2019YFC1806000）；国家自然科学基金资助项目（52078235）.

Corresponding Authors: Hefu PU E-mail: dengsy@hust.edu.cn;puh@hust.edu.cn

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Cite this article:

Shengyi DENG,Yongwei ZHOU,Hefu PU,Yuchao LI,Ming MIN. Numerical solution for contaminant transport in cutoff wall considering semipermeable membrane behavior. Journal of ZheJiang University (Engineering Science), 2025, 59(2): 342-350.

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https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2025.02.012 OR https://www.zjujournals.com/eng/Y2025/V59/I2/342

阻隔墙中考虑半透膜效应的污染物迁移数值解

建立膨润土系阻隔墙-含水层系统中考虑半透膜效应的污染物迁移数值模型，提出有限差分解法. 通过与现有的解析解、半透膜试验和COMSOL软件数值模拟的比较，验证了该数值解的有效性. 利用提出的数值解开展参数分析，研究半透膜效应、污染物源质量浓度、阻隔墙厚度、阻隔墙渗透系数和水力梯度对铅离子在阻隔墙-含水层系统中迁移规律的影响. 结果表明，半透膜效应对污染物迁移有显著影响，不考虑半透膜效应会较大地低估阻隔墙的击穿时间并高估污染物流出质量. 针对所分析的不同工况，当考虑半透膜效应时，污染物击穿时间提高了12.2%~79.6%，污染物质量通量减少了18.4%~62.3%. 当渗透系数从1×10^?8 m/s减小至1×10^?10 m/s时，质量通量减少了2个数量级，且是否考虑半透膜效应的差异由31.1%增加至97.5%. 提出的数值解能够考虑对流、分子扩散、机械弥散、半透膜效应、有效孔隙率等作用，可以用于膨润土系阻隔墙的设计和污染物迁移过程分析.

关键词： 阻隔墙, 污染物迁移, 半透膜效应

Fig.1 Schematic diagram of cutoff wall-aquifer system

Fig.2 Comparison of relative mass concentration profile between proposed numerical solution and Li et al.’s ^[18] analytical solution

Tab.1 Relevant parameter for semipermeable membrane test by Malusis et al. ^[19]

Fig.3 Comparison of cumulative mass outflow between proposed numerical solution and test of Malusis et al. ^[19]

Tab.2 Transport parameter of contaminant and material parameter of cutoff wall-aquifer system

Fig.4 Comparison between proposed numerical solution and numerical result of COMSOL

Fig.5 Effect of membrane efficiency coefficient on relative mass concentration and mass flux of contaminant

Fig.6 Effect of contaminant source mass concentration on relative mass concentration of contaminant

Fig.7 Effect of thickness of cutoff wall on breakthrough time for various distribution coefficient

Fig.8 Effect of hydraulic conductivity of cutoff wall on relative mass concentration and mass flux of contaminant


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