Tide-Induced Air Pressure Fluctuations in a Coastal Unsaturated Zone: Effects of Thin Low-Permeability Pavements



This paper presents an analytical case study to explore one-dimensional subsurface air pressure variation in a coastal three-layered unsaturated zone. The upper layer is thin and much less permeable than the middle layer, and water table is located in the very permeable lower layer. An analytical solution was derived to describe the air pressure variation caused by tide-induced water table fluctuations. We revisited the case study at Hong Kong International Airport conducted by Jiao and Li (2004) who used a two-dimensional numerical model. The analytical prediction using the parameter values equivalent to the two-dimensional numerical model agreed very well with the observed air pressure, indicating the validity and applicability of our one-dimensional model in approximating the actual situation in this coastal zone with adequate accuracy. The analysis revealed that the asphalt pavement played an important role in causing air pressure fluctuations below it. Abnormally high air pressure can be caused beneath the surface pavement when the air permeability decreases due to rainfall infiltration, which may lead to heaving problems during rising tides.