The effects of entrapped air and barometric fluctuations on the drainage of porous mediums

Abstract

A theory was developed for transient drainage of porous mediums taking into consideration the air that is entrapped within the flow region. The theory is based on the soil moisture diffusion equation with modifications made to include the effect of the entrapped air and the effect of changes in pressure due to barometric fluctuations. The theory was tested on a one‐dimensional flow sand model, and the results were compared with results obtained from a numerical solution of the developed equation. The theory and experiments show that barometric fluctuations have little effect on a draining column containing entrapped air when the column is open to the atmosphere at both ends. However, when the column is closed at the bottom, an increase in atmospheric pressure lowers the position of the water table, whereas a decrease in atmospheric pressure raises the water table. Both the experiments and the developed theory show a much greater change in the position of the water table with atmospheric pressure than a previous steady‐state theory.