Subsurface fluids injection is a viable alternative for controlling seawater intrusion in coastal regions, and freshwater is usually served for valid fluids to generate pressure ridge towards the ocean. But other fluids injection, such as compressed air, which presents clean and readily available, is a more attractive solution for repulsing the intruded seawater where freshwater is insufficient. In this study, the performance of compressed air injection (i.e., air barriers) for mitigating seawater intrusion in a coastal unconfined aquifer was quantificationally assessed using a coupled water-air two-phase flow and saltwater transport model. As compressed air is introduced into the aquifer at the toe of saltwater wedge, the seaward hydraulic gradient adjacent to the coast is produced driven by the generated airflow, thereby causing salt-freshwater interface to retreat to the ocean. The magnitude of air injection rate, related to the operational cost of air barriers, does not increases significantly given the progressively decreasing change rate. Compared to the workability of air barriers in the confined aquifer under similar conditions, the reduction in intruded seawater at 365.0 d in the unconfined aquifer reaches only about 0.45 times that in the confined aquifer, which indicates the significance of the boundary condition of aquifer top. The sensitivity analysis of the overlying unsaturated zone reveals that with its permeability decreasing or its thickness increasing, the performance of air barriers is enhanced owing to the blocking effect of the overlying layer on the escape of generated airflow and tends progressively to be stable. Particularly, the efficacy of air barriers in the confined aquifer, including the reduction in intruded seawater and the air injection rate, also can be achieved in an unconfined aquifer with an overlaying sufficient-semipermeable layer.

注入地下流体是控制沿海地区海水入侵的可行替代方法，通常将淡水用作有效流体，以产生朝向海洋的压力脊。但是其他注入的流体，例如压缩空气，表现出清洁且易于使用，是一种在淡水不足的情况下排斥注入海水的更具吸引力的解决方案。在这项研究中，使用耦合的水-气两相流和盐水传输模型定量评估了压缩空气注入（即空气屏障）缓解沿海无限制含水层中海水入侵的性能。当压缩空气在咸水楔的脚趾处引入含水层时，由产生的气流驱动产生与海岸相邻的向海水力梯度，从而导致盐-淡水界面向海洋退缩。考虑到变化率的逐渐降低，与空气屏障的运行成本相关的空气注入率的幅度不会显着增加。与密闭含水层在类似条件下的阻隔性相比，无密闭含水层中365.0 d的侵入海水减少量仅为密闭含水层的0.45倍，这说明了含水层顶部边界条件的重要性。对上覆不饱和带的敏感性分析表明，由于上覆层对所产生的气流逸出的阻挡作用，随着其渗透率的降低或厚度的增加，阻气层的性能得到增强，并且趋于稳定。尤其，