Laboratory Study of Steady-State Vertical Infiltration in Layered Soils

A series of steady-state vertical infiltration tests were conducted on a 1.0 m high soil column of Clayey Sand over Fine Sand under various boundary conditions. The test results show that the pore-water pressures in the Clayey Sand were always negative due to the existence of the underlying Fine Sand. The pore-water pressures in the Clayey Sand increased with the increase in flux or head at the upper boundary and the rise of the water table at the lower boundary, but the infiltration rate generally decreased following the rise of the lower water table. The unsaturated hydraulic conductivity values of the Clayey Sand were found to be closer to the predicted drying conductivity curve rather than to the wetting conductivity curve. The Clayey Sand was found to be unsaturated even when the measured pore-water pressures were either zero or positive suggesting possible air entrapment in the soil during the downward movement of water.