Water exclusion from tunnel cavities spanning a water table

The vertical downward flow of water in unsaturated soils is perturbed by the presence of cavities. Analysis of the flow problem has shown that there is for a given situation a critical shape of a cavity for it to exclude water entry when the soil–water pressure at the cavity wall is everywhere the air-entry value for the soil and the cavity wall is a streamline. In this note cavities spanning a water table are considered when the water table is caused by artesian pressure in a water-bearing substratum. Building on previous analysis, critical shapes for such cavities are obtained for particular circumstances, thus showing that situations can exist for cavities not to fill with water although protruding below the water table. It is noted that the analysis used to obtain a solution to this problem is the same as that for the groundwater seepage problem of water movement to a water-bearing substratum under pressure from infinite ponded-water regions separated by a long island strip.