Behavior of unsaturated layered soil columns during infiltration

This paper presents the laboratory test results of vertical infiltration on two soil columns of finer over coarser soils subject to simulated rainfalls under conditions of no-ponding at the surface and constant head at the bottom. The main objectives were to evaluate the effect of rainfall intensity and duration; and to provide experimental evidence for soil water redistribution and hysteresis. The results show that rainfall intensity had a major effect on infiltration in the finer layer but had limited effect in the coarser layer due to the large difference of saturated permeability between the two layers. A relatively short rainfall duration resulted in a delayed response of pore pressure and water content to the rainfall after its cessation, while a relatively long duration did not result in such a delayed response. The delayed response indicated the redistribution of soil water in infiltration. Different paths of water content versus matric suction were followed during the tests indicating the apparent hysteretic behavior of soil water. In addition, the coarser layer restricted the increase of pore pressure in the finer layer. A minor variation of saturated soil permeability had minimal effect on infiltration.