The electrokinetics methods have great potential to characterize hydrogeological processes in porous media, especially in complex partially saturated hydrosystems (e.g., the vadose zone). The dependence of the streaming coupling coefficient on water saturation remains highly debated in both theoretical and experimental works. In this work, we propose a physically based model for the streaming potential coupling coefficient in porous media during the flow of water and air under partially saturated conditions. The proposed model is linked to fluid electrical conductivity, water saturation, irreducible water saturation, and microstructural parameters of porous materials. In particular, the surface conductivity of porous media has been taken into account in the model. In addition, we also obtain an expression for the characteristic length scale at full saturation in this work. The proposed model is successfully validated using experimental data from literature. A relationship between the streaming potential coupling coefficient and the effective excess charge density is also obtained in this work and the result is the same as those proposed in literature using different approaches. The model proposes a simple and efficient way to model the streaming potential generation for partially saturated porous media and can be useful for hydrogeophysical studies in the critical zone.

中文翻译：

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部分饱和多孔介质中流动势耦合系数的物理模型

电动方法在表征多孔介质中的水文地质过程方面具有巨大潜力，特别是在复杂的部分饱和水系统（例如，包气带）中。在理论和实验工作中，流动耦合系数对含水饱和度的依赖性仍然存在很大争议。在这项工作中，我们提出了一个基于物理的模型，用于在部分饱和条件下水和空气流动期间多孔介质中的流动势耦合系数。所提出的模型与流体电导率、水饱和度、束缚水饱和度和多孔材料的微观结构参数相关联。特别是模型中考虑了多孔介质的表面电导率。此外，在这项工作中，我们还获得了完全饱和时特征长度尺度的表达式。使用文献中的实验数据成功验证了所提出的模型。在这项工作中还获得了流动电位耦合系数与有效过剩电荷密度之间的关系，结果与使用不同方法的文献中提出的结果相同。该模型提出了一种简单有效的方法来模拟部分饱和多孔介质的流动势生成，可用于关键区域的水文地球物理研究。在这项工作中还获得了流动电位耦合系数与有效过剩电荷密度之间的关系，结果与使用不同方法的文献中提出的结果相同。该模型提出了一种简单有效的方法来模拟部分饱和多孔介质的流动势生成，可用于关键区域的水文地球物理研究。在这项工作中还获得了流动电位耦合系数与有效过剩电荷密度之间的关系，结果与使用不同方法的文献中提出的结果相同。该模型提出了一种简单有效的方法来模拟部分饱和多孔介质的流动势生成，可用于关键区域的水文地球物理研究。