Semipermeable membrane effect is an important factor affecting the contaminant transport behavior through the bentonite-based barriers for waste containment. However, this effect has been ignored in majority of the existing analytical and numerical studies on contaminant transport, although it has been widely demonstrated in laboratory and field tests. Taking into account the semipermeable membrane effect, this study presents a numerical model for one-dimensional contaminant transport through a geosynthetic clay liner (GCL) composite cutoff wall-aquifer system consisting of a bentonite-based wall, a GCL and an aquifer. The finite difference method is used to obtain the solution. The numerical solution is validated against the laboratory experimental data, the existing analytical solution and COMSOL software simulations. A series of parametric analyses are conducted using the proposed numerical solution. The results indicate that the semipermeable membrane effect has a significant impact on the contaminant transport behavior and ignoring this effect can greatly underestimate the contaminant breakthrough time and overestimate contaminant outflow. For the conditions examined in this paper, the inclusion of semipermeable membrane effect results in a 7.1%∼78.6% increase in breakthrough time and a 5.3%∼40.7% decrease in mass flux, and the semipermeable membrane effect in bentonite-based wall, relative to that in the GCL, has greater impact on contaminant transport. The concentration-dependent semipermeable membrane efficiency coefficient ω more significantly slows down the contaminant transport relative to the constant ω, particularly under the conditions of low hydraulic conductivity, low source concentration and low hydraulic gradient. Moreover, it’s important to avoid simultaneous deterioration of both the bentonite-based wall and the GCL, otherwise the breakthrough time of the GCL composite cutoff wall can decrease significantly.

中文翻译：

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考虑半透膜效应的污染物通过 GCL 复合截留墙-含水层系统运移的有限差分解


半透膜效应是影响污染物通过膨润土基屏障进行废物收容运输行为的重要因素。然而，尽管这种影响已在实验室和现场测试中得到广泛证明，但在大多数现有的关于污染物迁移的分析和数值研究中都被忽视了。考虑到半透膜效应，本研究提出了一种通过由膨润土基墙、GCL 和含水层组成的土工合成粘土衬垫 （GCL） 复合防渗墙-含水层系统进行一维污染物输送的数值模型。有限差分法用于获得解。根据实验室实验数据、现有解析解和 COMSOL 软件仿真对数值解进行了验证。使用所提出的数值解进行了一系列参数分析。结果表明，半透膜效应对污染物的迁移行为有显著影响，忽视这一效应会大大低估污染物的突破时间，高估污染物的流出量。对于本文研究的条件，半透膜效应的加入导致穿透时间增加 7.1%∼78.6%，质量通量降低 5.3%∼40.7%，膨润土基壁中的半透膜效应相对于 GCL 中的半透膜效应对污染物迁移的影响更大。相对于常数 ω，浓度依赖性的半透膜效率系数 ω 更显着地减慢了污染物的迁移，特别是在低水力传导率、低水力传导率、低水力梯度的条件下。 此外，重要的是要避免膨润土基墙和 GCL 同时劣化，否则 GCL 复合防渗墙的贯穿时间会显着缩短。