The rise and fall of the groundwater level can drive air flow in the vadose zone. In turn, the air flow can interact with the water flow. When the unconfined aquifer is covered by a low-permeability media, the coupling of the water flow and the air flow is more obvious. In this study, a conceptual model is established for coupling of air flow and water flow in the vadose zone in response to rapid fluctuations of the water table. Water injection and drainage experiments are conducted in a double-layered sand column with a thick layer (80.5 cm) of coarse sand and a thin layer of fine sand as a low-permeability cap. Different cap thickness (2 cm, 5 cm, 7.5 cm) and different thickness of the vadose zone (30 cm, 40 cm) are set for the experiments. Negative pressure (NP)/positive pressure (PP) of the air in the vadose zone is observed in the drainage/injection experiments, with higher pressure in experiments of thicker cap layer. In each experiment, NP or PP increases rapidly to reach a maximum in the early stage, and gradually becomes zero in the late stage. Analytical solutions on three subdivided stages indicate the permeability and thickness of the cap layer, as well as permeability and porosity of the media in the vadose zone are the key controlling factors on the process of coupling of air flow and water flow. The solutions also reveal the formation mechanism of air pressure in the vadose zone with a low-permeability cap. This study has both theoretical significance and engineering applications.

中文翻译：

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地下水位上升或下降的无限制含水层中垂直气流的解析解

地下水位的上升和下降可以驱动渗流区内的气流。空气流又可以与水流相互作用。当无限制含水层被低渗透性介质覆盖时，水流与空气流的耦合更加明显。在这项研究中，建立了一个概念模型，用于响应水位的快速波动，耦合渗流区内的气流和水流。在双层砂柱中进行注水和排水实验，该双层砂柱具有厚层（80.5厘米）的粗砂和薄层的细砂作为低渗透率盖。实验设置了不同的瓶盖厚度（2 cm，5 cm，7.5 cm）和不同的渗流区厚度（30 cm，40 cm）。在排水/注入实验中观察到渗流区内空气的负压（NP）/正压（PP），而在较厚的盖层实验中则观察到较高的压力。在每个实验中，NP或PP迅速增加，在早期达到最大值，而在后期逐渐变为零。在三个细分阶段的分析结果表明，盖层的渗透率和厚度以及渗流带中介质的渗透率和孔隙率是影响气流和水流耦合过程的关键控制因素。该解决方案还揭示了具有低渗透率帽的渗流区内气压的形成机理。该研究具有理论意义和工程应用价值。在每个实验中，NP或PP迅速增加，在早期达到最大值，而在后期逐渐变为零。在三个细分阶段的分析结果表明，盖层的渗透率和厚度以及渗流带中介质的渗透率和孔隙率是影响气流和水流耦合过程的关键控制因素。该解决方案还揭示了具有低渗透率帽的渗流区内气压的形成机理。该研究具有理论意义和工程应用价值。在每个实验中，NP或PP迅速增加，在早期达到最大值，而在后期逐渐变为零。在三个细分阶段的分析结果表明，盖层的渗透率和厚度以及渗流带中介质的渗透率和孔隙率是影响气流和水流耦合过程的关键控制因素。该解决方案还揭示了具有低渗透率帽的渗流区内气压的形成机理。该研究具有理论意义和工程应用价值。渗流区内介质的渗透率和孔隙率是影响气流和水流耦合过程的关键控制因素。该解决方案还揭示了具有低渗透率帽的渗流区内气压的形成机理。该研究具有理论意义和工程应用价值。渗流区内介质的渗透率和孔隙率是影响气流和水流耦合过程的关键控制因素。该解决方案还揭示了具有低渗透率帽的渗流区内气压的形成机理。该研究具有理论意义和工程应用价值。